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Message-ID: <20210915141524.674661678@infradead.org>
Date: Wed, 15 Sep 2021 16:07:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: andrealmeid@...labora.com, tglx@...utronix.de, mingo@...hat.com,
dvhart@...radead.org, rostedt@...dmis.org, bigeasy@...utronix.de
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
kernel@...labora.com, krisman@...labora.com,
linux-api@...r.kernel.org, libc-alpha@...rceware.org,
mtk.manpages@...il.com, dave@...olabs.net, arnd@...db.de
Subject: [PATCH 01/20] futex: Move to kernel/futex/
In preparation for splitup..
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
MAINTAINERS | 2
kernel/Makefile | 2
kernel/futex.c | 4272 --------------------------------------------------
kernel/futex/Makefile | 3
kernel/futex/core.c | 4272 ++++++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 4277 insertions(+), 4274 deletions(-)
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7720,7 +7720,7 @@ F: Documentation/locking/*futex*
F: include/asm-generic/futex.h
F: include/linux/futex.h
F: include/uapi/linux/futex.h
-F: kernel/futex.c
+F: kernel/futex/*
F: tools/perf/bench/futex*
F: tools/testing/selftests/futex/
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -59,7 +59,7 @@ obj-$(CONFIG_FREEZER) += freezer.o
obj-$(CONFIG_PROFILING) += profile.o
obj-$(CONFIG_STACKTRACE) += stacktrace.o
obj-y += time/
-obj-$(CONFIG_FUTEX) += futex.o
+obj-$(CONFIG_FUTEX) += futex/
obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
obj-$(CONFIG_SMP) += smp.o
ifneq ($(CONFIG_SMP),y)
--- a/kernel/futex.c
+++ /dev/null
@@ -1,4272 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * Fast Userspace Mutexes (which I call "Futexes!").
- * (C) Rusty Russell, IBM 2002
- *
- * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
- * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
- *
- * Removed page pinning, fix privately mapped COW pages and other cleanups
- * (C) Copyright 2003, 2004 Jamie Lokier
- *
- * Robust futex support started by Ingo Molnar
- * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
- * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
- *
- * PI-futex support started by Ingo Molnar and Thomas Gleixner
- * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@...hat.com>
- * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@...esys.com>
- *
- * PRIVATE futexes by Eric Dumazet
- * Copyright (C) 2007 Eric Dumazet <dada1@...mosbay.com>
- *
- * Requeue-PI support by Darren Hart <dvhltc@...ibm.com>
- * Copyright (C) IBM Corporation, 2009
- * Thanks to Thomas Gleixner for conceptual design and careful reviews.
- *
- * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
- * enough at me, Linus for the original (flawed) idea, Matthew
- * Kirkwood for proof-of-concept implementation.
- *
- * "The futexes are also cursed."
- * "But they come in a choice of three flavours!"
- */
-#include <linux/compat.h>
-#include <linux/jhash.h>
-#include <linux/pagemap.h>
-#include <linux/syscalls.h>
-#include <linux/freezer.h>
-#include <linux/memblock.h>
-#include <linux/fault-inject.h>
-#include <linux/time_namespace.h>
-
-#include <asm/futex.h>
-
-#include "locking/rtmutex_common.h"
-
-/*
- * READ this before attempting to hack on futexes!
- *
- * Basic futex operation and ordering guarantees
- * =============================================
- *
- * The waiter reads the futex value in user space and calls
- * futex_wait(). This function computes the hash bucket and acquires
- * the hash bucket lock. After that it reads the futex user space value
- * again and verifies that the data has not changed. If it has not changed
- * it enqueues itself into the hash bucket, releases the hash bucket lock
- * and schedules.
- *
- * The waker side modifies the user space value of the futex and calls
- * futex_wake(). This function computes the hash bucket and acquires the
- * hash bucket lock. Then it looks for waiters on that futex in the hash
- * bucket and wakes them.
- *
- * In futex wake up scenarios where no tasks are blocked on a futex, taking
- * the hb spinlock can be avoided and simply return. In order for this
- * optimization to work, ordering guarantees must exist so that the waiter
- * being added to the list is acknowledged when the list is concurrently being
- * checked by the waker, avoiding scenarios like the following:
- *
- * CPU 0 CPU 1
- * val = *futex;
- * sys_futex(WAIT, futex, val);
- * futex_wait(futex, val);
- * uval = *futex;
- * *futex = newval;
- * sys_futex(WAKE, futex);
- * futex_wake(futex);
- * if (queue_empty())
- * return;
- * if (uval == val)
- * lock(hash_bucket(futex));
- * queue();
- * unlock(hash_bucket(futex));
- * schedule();
- *
- * This would cause the waiter on CPU 0 to wait forever because it
- * missed the transition of the user space value from val to newval
- * and the waker did not find the waiter in the hash bucket queue.
- *
- * The correct serialization ensures that a waiter either observes
- * the changed user space value before blocking or is woken by a
- * concurrent waker:
- *
- * CPU 0 CPU 1
- * val = *futex;
- * sys_futex(WAIT, futex, val);
- * futex_wait(futex, val);
- *
- * waiters++; (a)
- * smp_mb(); (A) <-- paired with -.
- * |
- * lock(hash_bucket(futex)); |
- * |
- * uval = *futex; |
- * | *futex = newval;
- * | sys_futex(WAKE, futex);
- * | futex_wake(futex);
- * |
- * `--------> smp_mb(); (B)
- * if (uval == val)
- * queue();
- * unlock(hash_bucket(futex));
- * schedule(); if (waiters)
- * lock(hash_bucket(futex));
- * else wake_waiters(futex);
- * waiters--; (b) unlock(hash_bucket(futex));
- *
- * Where (A) orders the waiters increment and the futex value read through
- * atomic operations (see hb_waiters_inc) and where (B) orders the write
- * to futex and the waiters read (see hb_waiters_pending()).
- *
- * This yields the following case (where X:=waiters, Y:=futex):
- *
- * X = Y = 0
- *
- * w[X]=1 w[Y]=1
- * MB MB
- * r[Y]=y r[X]=x
- *
- * Which guarantees that x==0 && y==0 is impossible; which translates back into
- * the guarantee that we cannot both miss the futex variable change and the
- * enqueue.
- *
- * Note that a new waiter is accounted for in (a) even when it is possible that
- * the wait call can return error, in which case we backtrack from it in (b).
- * Refer to the comment in queue_lock().
- *
- * Similarly, in order to account for waiters being requeued on another
- * address we always increment the waiters for the destination bucket before
- * acquiring the lock. It then decrements them again after releasing it -
- * the code that actually moves the futex(es) between hash buckets (requeue_futex)
- * will do the additional required waiter count housekeeping. This is done for
- * double_lock_hb() and double_unlock_hb(), respectively.
- */
-
-#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
-#define futex_cmpxchg_enabled 1
-#else
-static int __read_mostly futex_cmpxchg_enabled;
-#endif
-
-/*
- * Futex flags used to encode options to functions and preserve them across
- * restarts.
- */
-#ifdef CONFIG_MMU
-# define FLAGS_SHARED 0x01
-#else
-/*
- * NOMMU does not have per process address space. Let the compiler optimize
- * code away.
- */
-# define FLAGS_SHARED 0x00
-#endif
-#define FLAGS_CLOCKRT 0x02
-#define FLAGS_HAS_TIMEOUT 0x04
-
-/*
- * Priority Inheritance state:
- */
-struct futex_pi_state {
- /*
- * list of 'owned' pi_state instances - these have to be
- * cleaned up in do_exit() if the task exits prematurely:
- */
- struct list_head list;
-
- /*
- * The PI object:
- */
- struct rt_mutex_base pi_mutex;
-
- struct task_struct *owner;
- refcount_t refcount;
-
- union futex_key key;
-} __randomize_layout;
-
-/**
- * struct futex_q - The hashed futex queue entry, one per waiting task
- * @list: priority-sorted list of tasks waiting on this futex
- * @task: the task waiting on the futex
- * @lock_ptr: the hash bucket lock
- * @key: the key the futex is hashed on
- * @pi_state: optional priority inheritance state
- * @rt_waiter: rt_waiter storage for use with requeue_pi
- * @requeue_pi_key: the requeue_pi target futex key
- * @bitset: bitset for the optional bitmasked wakeup
- * @requeue_state: State field for futex_requeue_pi()
- * @requeue_wait: RCU wait for futex_requeue_pi() (RT only)
- *
- * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
- * we can wake only the relevant ones (hashed queues may be shared).
- *
- * A futex_q has a woken state, just like tasks have TASK_RUNNING.
- * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
- * The order of wakeup is always to make the first condition true, then
- * the second.
- *
- * PI futexes are typically woken before they are removed from the hash list via
- * the rt_mutex code. See unqueue_me_pi().
- */
-struct futex_q {
- struct plist_node list;
-
- struct task_struct *task;
- spinlock_t *lock_ptr;
- union futex_key key;
- struct futex_pi_state *pi_state;
- struct rt_mutex_waiter *rt_waiter;
- union futex_key *requeue_pi_key;
- u32 bitset;
- atomic_t requeue_state;
-#ifdef CONFIG_PREEMPT_RT
- struct rcuwait requeue_wait;
-#endif
-} __randomize_layout;
-
-/*
- * On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
- * underlying rtmutex. The task which is about to be requeued could have
- * just woken up (timeout, signal). After the wake up the task has to
- * acquire hash bucket lock, which is held by the requeue code. As a task
- * can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking
- * and the hash bucket lock blocking would collide and corrupt state.
- *
- * On !PREEMPT_RT this is not a problem and everything could be serialized
- * on hash bucket lock, but aside of having the benefit of common code,
- * this allows to avoid doing the requeue when the task is already on the
- * way out and taking the hash bucket lock of the original uaddr1 when the
- * requeue has been completed.
- *
- * The following state transitions are valid:
- *
- * On the waiter side:
- * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IGNORE
- * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT
- *
- * On the requeue side:
- * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_INPROGRESS
- * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_DONE/LOCKED
- * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_NONE (requeue failed)
- * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_DONE/LOCKED
- * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_IGNORE (requeue failed)
- *
- * The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this
- * signals that the waiter is already on the way out. It also means that
- * the waiter is still on the 'wait' futex, i.e. uaddr1.
- *
- * The waiter side signals early wakeup to the requeue side either through
- * setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending
- * on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately
- * proceed to take the hash bucket lock of uaddr1. If it set state to WAIT,
- * which means the wakeup is interleaving with a requeue in progress it has
- * to wait for the requeue side to change the state. Either to DONE/LOCKED
- * or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex
- * and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by
- * the requeue side when the requeue attempt failed via deadlock detection
- * and therefore the waiter q is still on the uaddr1 futex.
- */
-enum {
- Q_REQUEUE_PI_NONE = 0,
- Q_REQUEUE_PI_IGNORE,
- Q_REQUEUE_PI_IN_PROGRESS,
- Q_REQUEUE_PI_WAIT,
- Q_REQUEUE_PI_DONE,
- Q_REQUEUE_PI_LOCKED,
-};
-
-static const struct futex_q futex_q_init = {
- /* list gets initialized in queue_me()*/
- .key = FUTEX_KEY_INIT,
- .bitset = FUTEX_BITSET_MATCH_ANY,
- .requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE),
-};
-
-/*
- * Hash buckets are shared by all the futex_keys that hash to the same
- * location. Each key may have multiple futex_q structures, one for each task
- * waiting on a futex.
- */
-struct futex_hash_bucket {
- atomic_t waiters;
- spinlock_t lock;
- struct plist_head chain;
-} ____cacheline_aligned_in_smp;
-
-/*
- * The base of the bucket array and its size are always used together
- * (after initialization only in hash_futex()), so ensure that they
- * reside in the same cacheline.
- */
-static struct {
- struct futex_hash_bucket *queues;
- unsigned long hashsize;
-} __futex_data __read_mostly __aligned(2*sizeof(long));
-#define futex_queues (__futex_data.queues)
-#define futex_hashsize (__futex_data.hashsize)
-
-
-/*
- * Fault injections for futexes.
- */
-#ifdef CONFIG_FAIL_FUTEX
-
-static struct {
- struct fault_attr attr;
-
- bool ignore_private;
-} fail_futex = {
- .attr = FAULT_ATTR_INITIALIZER,
- .ignore_private = false,
-};
-
-static int __init setup_fail_futex(char *str)
-{
- return setup_fault_attr(&fail_futex.attr, str);
-}
-__setup("fail_futex=", setup_fail_futex);
-
-static bool should_fail_futex(bool fshared)
-{
- if (fail_futex.ignore_private && !fshared)
- return false;
-
- return should_fail(&fail_futex.attr, 1);
-}
-
-#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
-
-static int __init fail_futex_debugfs(void)
-{
- umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
- struct dentry *dir;
-
- dir = fault_create_debugfs_attr("fail_futex", NULL,
- &fail_futex.attr);
- if (IS_ERR(dir))
- return PTR_ERR(dir);
-
- debugfs_create_bool("ignore-private", mode, dir,
- &fail_futex.ignore_private);
- return 0;
-}
-
-late_initcall(fail_futex_debugfs);
-
-#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
-
-#else
-static inline bool should_fail_futex(bool fshared)
-{
- return false;
-}
-#endif /* CONFIG_FAIL_FUTEX */
-
-#ifdef CONFIG_COMPAT
-static void compat_exit_robust_list(struct task_struct *curr);
-#endif
-
-/*
- * Reflects a new waiter being added to the waitqueue.
- */
-static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
- atomic_inc(&hb->waiters);
- /*
- * Full barrier (A), see the ordering comment above.
- */
- smp_mb__after_atomic();
-#endif
-}
-
-/*
- * Reflects a waiter being removed from the waitqueue by wakeup
- * paths.
- */
-static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
- atomic_dec(&hb->waiters);
-#endif
-}
-
-static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
- /*
- * Full barrier (B), see the ordering comment above.
- */
- smp_mb();
- return atomic_read(&hb->waiters);
-#else
- return 1;
-#endif
-}
-
-/**
- * hash_futex - Return the hash bucket in the global hash
- * @key: Pointer to the futex key for which the hash is calculated
- *
- * We hash on the keys returned from get_futex_key (see below) and return the
- * corresponding hash bucket in the global hash.
- */
-static struct futex_hash_bucket *hash_futex(union futex_key *key)
-{
- u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
- key->both.offset);
-
- return &futex_queues[hash & (futex_hashsize - 1)];
-}
-
-
-/**
- * match_futex - Check whether two futex keys are equal
- * @key1: Pointer to key1
- * @key2: Pointer to key2
- *
- * Return 1 if two futex_keys are equal, 0 otherwise.
- */
-static inline int match_futex(union futex_key *key1, union futex_key *key2)
-{
- return (key1 && key2
- && key1->both.word == key2->both.word
- && key1->both.ptr == key2->both.ptr
- && key1->both.offset == key2->both.offset);
-}
-
-enum futex_access {
- FUTEX_READ,
- FUTEX_WRITE
-};
-
-/**
- * futex_setup_timer - set up the sleeping hrtimer.
- * @time: ptr to the given timeout value
- * @timeout: the hrtimer_sleeper structure to be set up
- * @flags: futex flags
- * @range_ns: optional range in ns
- *
- * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
- * value given
- */
-static inline struct hrtimer_sleeper *
-futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
- int flags, u64 range_ns)
-{
- if (!time)
- return NULL;
-
- hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
- CLOCK_REALTIME : CLOCK_MONOTONIC,
- HRTIMER_MODE_ABS);
- /*
- * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
- * effectively the same as calling hrtimer_set_expires().
- */
- hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
-
- return timeout;
-}
-
-/*
- * Generate a machine wide unique identifier for this inode.
- *
- * This relies on u64 not wrapping in the life-time of the machine; which with
- * 1ns resolution means almost 585 years.
- *
- * This further relies on the fact that a well formed program will not unmap
- * the file while it has a (shared) futex waiting on it. This mapping will have
- * a file reference which pins the mount and inode.
- *
- * If for some reason an inode gets evicted and read back in again, it will get
- * a new sequence number and will _NOT_ match, even though it is the exact same
- * file.
- *
- * It is important that match_futex() will never have a false-positive, esp.
- * for PI futexes that can mess up the state. The above argues that false-negatives
- * are only possible for malformed programs.
- */
-static u64 get_inode_sequence_number(struct inode *inode)
-{
- static atomic64_t i_seq;
- u64 old;
-
- /* Does the inode already have a sequence number? */
- old = atomic64_read(&inode->i_sequence);
- if (likely(old))
- return old;
-
- for (;;) {
- u64 new = atomic64_add_return(1, &i_seq);
- if (WARN_ON_ONCE(!new))
- continue;
-
- old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
- if (old)
- return old;
- return new;
- }
-}
-
-/**
- * get_futex_key() - Get parameters which are the keys for a futex
- * @uaddr: virtual address of the futex
- * @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
- * @key: address where result is stored.
- * @rw: mapping needs to be read/write (values: FUTEX_READ,
- * FUTEX_WRITE)
- *
- * Return: a negative error code or 0
- *
- * The key words are stored in @key on success.
- *
- * For shared mappings (when @fshared), the key is:
- *
- * ( inode->i_sequence, page->index, offset_within_page )
- *
- * [ also see get_inode_sequence_number() ]
- *
- * For private mappings (or when !@...ared), the key is:
- *
- * ( current->mm, address, 0 )
- *
- * This allows (cross process, where applicable) identification of the futex
- * without keeping the page pinned for the duration of the FUTEX_WAIT.
- *
- * lock_page() might sleep, the caller should not hold a spinlock.
- */
-static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
- enum futex_access rw)
-{
- unsigned long address = (unsigned long)uaddr;
- struct mm_struct *mm = current->mm;
- struct page *page, *tail;
- struct address_space *mapping;
- int err, ro = 0;
-
- /*
- * The futex address must be "naturally" aligned.
- */
- key->both.offset = address % PAGE_SIZE;
- if (unlikely((address % sizeof(u32)) != 0))
- return -EINVAL;
- address -= key->both.offset;
-
- if (unlikely(!access_ok(uaddr, sizeof(u32))))
- return -EFAULT;
-
- if (unlikely(should_fail_futex(fshared)))
- return -EFAULT;
-
- /*
- * PROCESS_PRIVATE futexes are fast.
- * As the mm cannot disappear under us and the 'key' only needs
- * virtual address, we dont even have to find the underlying vma.
- * Note : We do have to check 'uaddr' is a valid user address,
- * but access_ok() should be faster than find_vma()
- */
- if (!fshared) {
- key->private.mm = mm;
- key->private.address = address;
- return 0;
- }
-
-again:
- /* Ignore any VERIFY_READ mapping (futex common case) */
- if (unlikely(should_fail_futex(true)))
- return -EFAULT;
-
- err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
- /*
- * If write access is not required (eg. FUTEX_WAIT), try
- * and get read-only access.
- */
- if (err == -EFAULT && rw == FUTEX_READ) {
- err = get_user_pages_fast(address, 1, 0, &page);
- ro = 1;
- }
- if (err < 0)
- return err;
- else
- err = 0;
-
- /*
- * The treatment of mapping from this point on is critical. The page
- * lock protects many things but in this context the page lock
- * stabilizes mapping, prevents inode freeing in the shared
- * file-backed region case and guards against movement to swap cache.
- *
- * Strictly speaking the page lock is not needed in all cases being
- * considered here and page lock forces unnecessarily serialization
- * From this point on, mapping will be re-verified if necessary and
- * page lock will be acquired only if it is unavoidable
- *
- * Mapping checks require the head page for any compound page so the
- * head page and mapping is looked up now. For anonymous pages, it
- * does not matter if the page splits in the future as the key is
- * based on the address. For filesystem-backed pages, the tail is
- * required as the index of the page determines the key. For
- * base pages, there is no tail page and tail == page.
- */
- tail = page;
- page = compound_head(page);
- mapping = READ_ONCE(page->mapping);
-
- /*
- * If page->mapping is NULL, then it cannot be a PageAnon
- * page; but it might be the ZERO_PAGE or in the gate area or
- * in a special mapping (all cases which we are happy to fail);
- * or it may have been a good file page when get_user_pages_fast
- * found it, but truncated or holepunched or subjected to
- * invalidate_complete_page2 before we got the page lock (also
- * cases which we are happy to fail). And we hold a reference,
- * so refcount care in invalidate_complete_page's remove_mapping
- * prevents drop_caches from setting mapping to NULL beneath us.
- *
- * The case we do have to guard against is when memory pressure made
- * shmem_writepage move it from filecache to swapcache beneath us:
- * an unlikely race, but we do need to retry for page->mapping.
- */
- if (unlikely(!mapping)) {
- int shmem_swizzled;
-
- /*
- * Page lock is required to identify which special case above
- * applies. If this is really a shmem page then the page lock
- * will prevent unexpected transitions.
- */
- lock_page(page);
- shmem_swizzled = PageSwapCache(page) || page->mapping;
- unlock_page(page);
- put_page(page);
-
- if (shmem_swizzled)
- goto again;
-
- return -EFAULT;
- }
-
- /*
- * Private mappings are handled in a simple way.
- *
- * If the futex key is stored on an anonymous page, then the associated
- * object is the mm which is implicitly pinned by the calling process.
- *
- * NOTE: When userspace waits on a MAP_SHARED mapping, even if
- * it's a read-only handle, it's expected that futexes attach to
- * the object not the particular process.
- */
- if (PageAnon(page)) {
- /*
- * A RO anonymous page will never change and thus doesn't make
- * sense for futex operations.
- */
- if (unlikely(should_fail_futex(true)) || ro) {
- err = -EFAULT;
- goto out;
- }
-
- key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
- key->private.mm = mm;
- key->private.address = address;
-
- } else {
- struct inode *inode;
-
- /*
- * The associated futex object in this case is the inode and
- * the page->mapping must be traversed. Ordinarily this should
- * be stabilised under page lock but it's not strictly
- * necessary in this case as we just want to pin the inode, not
- * update the radix tree or anything like that.
- *
- * The RCU read lock is taken as the inode is finally freed
- * under RCU. If the mapping still matches expectations then the
- * mapping->host can be safely accessed as being a valid inode.
- */
- rcu_read_lock();
-
- if (READ_ONCE(page->mapping) != mapping) {
- rcu_read_unlock();
- put_page(page);
-
- goto again;
- }
-
- inode = READ_ONCE(mapping->host);
- if (!inode) {
- rcu_read_unlock();
- put_page(page);
-
- goto again;
- }
-
- key->both.offset |= FUT_OFF_INODE; /* inode-based key */
- key->shared.i_seq = get_inode_sequence_number(inode);
- key->shared.pgoff = page_to_pgoff(tail);
- rcu_read_unlock();
- }
-
-out:
- put_page(page);
- return err;
-}
-
-/**
- * fault_in_user_writeable() - Fault in user address and verify RW access
- * @uaddr: pointer to faulting user space address
- *
- * Slow path to fixup the fault we just took in the atomic write
- * access to @uaddr.
- *
- * We have no generic implementation of a non-destructive write to the
- * user address. We know that we faulted in the atomic pagefault
- * disabled section so we can as well avoid the #PF overhead by
- * calling get_user_pages() right away.
- */
-static int fault_in_user_writeable(u32 __user *uaddr)
-{
- struct mm_struct *mm = current->mm;
- int ret;
-
- mmap_read_lock(mm);
- ret = fixup_user_fault(mm, (unsigned long)uaddr,
- FAULT_FLAG_WRITE, NULL);
- mmap_read_unlock(mm);
-
- return ret < 0 ? ret : 0;
-}
-
-/**
- * futex_top_waiter() - Return the highest priority waiter on a futex
- * @hb: the hash bucket the futex_q's reside in
- * @key: the futex key (to distinguish it from other futex futex_q's)
- *
- * Must be called with the hb lock held.
- */
-static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
- union futex_key *key)
-{
- struct futex_q *this;
-
- plist_for_each_entry(this, &hb->chain, list) {
- if (match_futex(&this->key, key))
- return this;
- }
- return NULL;
-}
-
-static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
- u32 uval, u32 newval)
-{
- int ret;
-
- pagefault_disable();
- ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
- pagefault_enable();
-
- return ret;
-}
-
-static int get_futex_value_locked(u32 *dest, u32 __user *from)
-{
- int ret;
-
- pagefault_disable();
- ret = __get_user(*dest, from);
- pagefault_enable();
-
- return ret ? -EFAULT : 0;
-}
-
-
-/*
- * PI code:
- */
-static int refill_pi_state_cache(void)
-{
- struct futex_pi_state *pi_state;
-
- if (likely(current->pi_state_cache))
- return 0;
-
- pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
-
- if (!pi_state)
- return -ENOMEM;
-
- INIT_LIST_HEAD(&pi_state->list);
- /* pi_mutex gets initialized later */
- pi_state->owner = NULL;
- refcount_set(&pi_state->refcount, 1);
- pi_state->key = FUTEX_KEY_INIT;
-
- current->pi_state_cache = pi_state;
-
- return 0;
-}
-
-static struct futex_pi_state *alloc_pi_state(void)
-{
- struct futex_pi_state *pi_state = current->pi_state_cache;
-
- WARN_ON(!pi_state);
- current->pi_state_cache = NULL;
-
- return pi_state;
-}
-
-static void pi_state_update_owner(struct futex_pi_state *pi_state,
- struct task_struct *new_owner)
-{
- struct task_struct *old_owner = pi_state->owner;
-
- lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
-
- if (old_owner) {
- raw_spin_lock(&old_owner->pi_lock);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- raw_spin_unlock(&old_owner->pi_lock);
- }
-
- if (new_owner) {
- raw_spin_lock(&new_owner->pi_lock);
- WARN_ON(!list_empty(&pi_state->list));
- list_add(&pi_state->list, &new_owner->pi_state_list);
- pi_state->owner = new_owner;
- raw_spin_unlock(&new_owner->pi_lock);
- }
-}
-
-static void get_pi_state(struct futex_pi_state *pi_state)
-{
- WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
-}
-
-/*
- * Drops a reference to the pi_state object and frees or caches it
- * when the last reference is gone.
- */
-static void put_pi_state(struct futex_pi_state *pi_state)
-{
- if (!pi_state)
- return;
-
- if (!refcount_dec_and_test(&pi_state->refcount))
- return;
-
- /*
- * If pi_state->owner is NULL, the owner is most probably dying
- * and has cleaned up the pi_state already
- */
- if (pi_state->owner) {
- unsigned long flags;
-
- raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
- pi_state_update_owner(pi_state, NULL);
- rt_mutex_proxy_unlock(&pi_state->pi_mutex);
- raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
- }
-
- if (current->pi_state_cache) {
- kfree(pi_state);
- } else {
- /*
- * pi_state->list is already empty.
- * clear pi_state->owner.
- * refcount is at 0 - put it back to 1.
- */
- pi_state->owner = NULL;
- refcount_set(&pi_state->refcount, 1);
- current->pi_state_cache = pi_state;
- }
-}
-
-#ifdef CONFIG_FUTEX_PI
-
-/*
- * This task is holding PI mutexes at exit time => bad.
- * Kernel cleans up PI-state, but userspace is likely hosed.
- * (Robust-futex cleanup is separate and might save the day for userspace.)
- */
-static void exit_pi_state_list(struct task_struct *curr)
-{
- struct list_head *next, *head = &curr->pi_state_list;
- struct futex_pi_state *pi_state;
- struct futex_hash_bucket *hb;
- union futex_key key = FUTEX_KEY_INIT;
-
- if (!futex_cmpxchg_enabled)
- return;
- /*
- * We are a ZOMBIE and nobody can enqueue itself on
- * pi_state_list anymore, but we have to be careful
- * versus waiters unqueueing themselves:
- */
- raw_spin_lock_irq(&curr->pi_lock);
- while (!list_empty(head)) {
- next = head->next;
- pi_state = list_entry(next, struct futex_pi_state, list);
- key = pi_state->key;
- hb = hash_futex(&key);
-
- /*
- * We can race against put_pi_state() removing itself from the
- * list (a waiter going away). put_pi_state() will first
- * decrement the reference count and then modify the list, so
- * its possible to see the list entry but fail this reference
- * acquire.
- *
- * In that case; drop the locks to let put_pi_state() make
- * progress and retry the loop.
- */
- if (!refcount_inc_not_zero(&pi_state->refcount)) {
- raw_spin_unlock_irq(&curr->pi_lock);
- cpu_relax();
- raw_spin_lock_irq(&curr->pi_lock);
- continue;
- }
- raw_spin_unlock_irq(&curr->pi_lock);
-
- spin_lock(&hb->lock);
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
- raw_spin_lock(&curr->pi_lock);
- /*
- * We dropped the pi-lock, so re-check whether this
- * task still owns the PI-state:
- */
- if (head->next != next) {
- /* retain curr->pi_lock for the loop invariant */
- raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
- spin_unlock(&hb->lock);
- put_pi_state(pi_state);
- continue;
- }
-
- WARN_ON(pi_state->owner != curr);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- pi_state->owner = NULL;
-
- raw_spin_unlock(&curr->pi_lock);
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- spin_unlock(&hb->lock);
-
- rt_mutex_futex_unlock(&pi_state->pi_mutex);
- put_pi_state(pi_state);
-
- raw_spin_lock_irq(&curr->pi_lock);
- }
- raw_spin_unlock_irq(&curr->pi_lock);
-}
-#else
-static inline void exit_pi_state_list(struct task_struct *curr) { }
-#endif
-
-/*
- * We need to check the following states:
- *
- * Waiter | pi_state | pi->owner | uTID | uODIED | ?
- *
- * [1] NULL | --- | --- | 0 | 0/1 | Valid
- * [2] NULL | --- | --- | >0 | 0/1 | Valid
- *
- * [3] Found | NULL | -- | Any | 0/1 | Invalid
- *
- * [4] Found | Found | NULL | 0 | 1 | Valid
- * [5] Found | Found | NULL | >0 | 1 | Invalid
- *
- * [6] Found | Found | task | 0 | 1 | Valid
- *
- * [7] Found | Found | NULL | Any | 0 | Invalid
- *
- * [8] Found | Found | task | ==taskTID | 0/1 | Valid
- * [9] Found | Found | task | 0 | 0 | Invalid
- * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
- *
- * [1] Indicates that the kernel can acquire the futex atomically. We
- * came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
- *
- * [2] Valid, if TID does not belong to a kernel thread. If no matching
- * thread is found then it indicates that the owner TID has died.
- *
- * [3] Invalid. The waiter is queued on a non PI futex
- *
- * [4] Valid state after exit_robust_list(), which sets the user space
- * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
- *
- * [5] The user space value got manipulated between exit_robust_list()
- * and exit_pi_state_list()
- *
- * [6] Valid state after exit_pi_state_list() which sets the new owner in
- * the pi_state but cannot access the user space value.
- *
- * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
- *
- * [8] Owner and user space value match
- *
- * [9] There is no transient state which sets the user space TID to 0
- * except exit_robust_list(), but this is indicated by the
- * FUTEX_OWNER_DIED bit. See [4]
- *
- * [10] There is no transient state which leaves owner and user space
- * TID out of sync. Except one error case where the kernel is denied
- * write access to the user address, see fixup_pi_state_owner().
- *
- *
- * Serialization and lifetime rules:
- *
- * hb->lock:
- *
- * hb -> futex_q, relation
- * futex_q -> pi_state, relation
- *
- * (cannot be raw because hb can contain arbitrary amount
- * of futex_q's)
- *
- * pi_mutex->wait_lock:
- *
- * {uval, pi_state}
- *
- * (and pi_mutex 'obviously')
- *
- * p->pi_lock:
- *
- * p->pi_state_list -> pi_state->list, relation
- * pi_mutex->owner -> pi_state->owner, relation
- *
- * pi_state->refcount:
- *
- * pi_state lifetime
- *
- *
- * Lock order:
- *
- * hb->lock
- * pi_mutex->wait_lock
- * p->pi_lock
- *
- */
-
-/*
- * Validate that the existing waiter has a pi_state and sanity check
- * the pi_state against the user space value. If correct, attach to
- * it.
- */
-static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
- struct futex_pi_state *pi_state,
- struct futex_pi_state **ps)
-{
- pid_t pid = uval & FUTEX_TID_MASK;
- u32 uval2;
- int ret;
-
- /*
- * Userspace might have messed up non-PI and PI futexes [3]
- */
- if (unlikely(!pi_state))
- return -EINVAL;
-
- /*
- * We get here with hb->lock held, and having found a
- * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
- * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
- * which in turn means that futex_lock_pi() still has a reference on
- * our pi_state.
- *
- * The waiter holding a reference on @pi_state also protects against
- * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
- * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
- * free pi_state before we can take a reference ourselves.
- */
- WARN_ON(!refcount_read(&pi_state->refcount));
-
- /*
- * Now that we have a pi_state, we can acquire wait_lock
- * and do the state validation.
- */
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
- /*
- * Since {uval, pi_state} is serialized by wait_lock, and our current
- * uval was read without holding it, it can have changed. Verify it
- * still is what we expect it to be, otherwise retry the entire
- * operation.
- */
- if (get_futex_value_locked(&uval2, uaddr))
- goto out_efault;
-
- if (uval != uval2)
- goto out_eagain;
-
- /*
- * Handle the owner died case:
- */
- if (uval & FUTEX_OWNER_DIED) {
- /*
- * exit_pi_state_list sets owner to NULL and wakes the
- * topmost waiter. The task which acquires the
- * pi_state->rt_mutex will fixup owner.
- */
- if (!pi_state->owner) {
- /*
- * No pi state owner, but the user space TID
- * is not 0. Inconsistent state. [5]
- */
- if (pid)
- goto out_einval;
- /*
- * Take a ref on the state and return success. [4]
- */
- goto out_attach;
- }
-
- /*
- * If TID is 0, then either the dying owner has not
- * yet executed exit_pi_state_list() or some waiter
- * acquired the rtmutex in the pi state, but did not
- * yet fixup the TID in user space.
- *
- * Take a ref on the state and return success. [6]
- */
- if (!pid)
- goto out_attach;
- } else {
- /*
- * If the owner died bit is not set, then the pi_state
- * must have an owner. [7]
- */
- if (!pi_state->owner)
- goto out_einval;
- }
-
- /*
- * Bail out if user space manipulated the futex value. If pi
- * state exists then the owner TID must be the same as the
- * user space TID. [9/10]
- */
- if (pid != task_pid_vnr(pi_state->owner))
- goto out_einval;
-
-out_attach:
- get_pi_state(pi_state);
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- *ps = pi_state;
- return 0;
-
-out_einval:
- ret = -EINVAL;
- goto out_error;
-
-out_eagain:
- ret = -EAGAIN;
- goto out_error;
-
-out_efault:
- ret = -EFAULT;
- goto out_error;
-
-out_error:
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- return ret;
-}
-
-/**
- * wait_for_owner_exiting - Block until the owner has exited
- * @ret: owner's current futex lock status
- * @exiting: Pointer to the exiting task
- *
- * Caller must hold a refcount on @exiting.
- */
-static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
-{
- if (ret != -EBUSY) {
- WARN_ON_ONCE(exiting);
- return;
- }
-
- if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
- return;
-
- mutex_lock(&exiting->futex_exit_mutex);
- /*
- * No point in doing state checking here. If the waiter got here
- * while the task was in exec()->exec_futex_release() then it can
- * have any FUTEX_STATE_* value when the waiter has acquired the
- * mutex. OK, if running, EXITING or DEAD if it reached exit()
- * already. Highly unlikely and not a problem. Just one more round
- * through the futex maze.
- */
- mutex_unlock(&exiting->futex_exit_mutex);
-
- put_task_struct(exiting);
-}
-
-static int handle_exit_race(u32 __user *uaddr, u32 uval,
- struct task_struct *tsk)
-{
- u32 uval2;
-
- /*
- * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
- * caller that the alleged owner is busy.
- */
- if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
- return -EBUSY;
-
- /*
- * Reread the user space value to handle the following situation:
- *
- * CPU0 CPU1
- *
- * sys_exit() sys_futex()
- * do_exit() futex_lock_pi()
- * futex_lock_pi_atomic()
- * exit_signals(tsk) No waiters:
- * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
- * mm_release(tsk) Set waiter bit
- * exit_robust_list(tsk) { *uaddr = 0x80000PID;
- * Set owner died attach_to_pi_owner() {
- * *uaddr = 0xC0000000; tsk = get_task(PID);
- * } if (!tsk->flags & PF_EXITING) {
- * ... attach();
- * tsk->futex_state = } else {
- * FUTEX_STATE_DEAD; if (tsk->futex_state !=
- * FUTEX_STATE_DEAD)
- * return -EAGAIN;
- * return -ESRCH; <--- FAIL
- * }
- *
- * Returning ESRCH unconditionally is wrong here because the
- * user space value has been changed by the exiting task.
- *
- * The same logic applies to the case where the exiting task is
- * already gone.
- */
- if (get_futex_value_locked(&uval2, uaddr))
- return -EFAULT;
-
- /* If the user space value has changed, try again. */
- if (uval2 != uval)
- return -EAGAIN;
-
- /*
- * The exiting task did not have a robust list, the robust list was
- * corrupted or the user space value in *uaddr is simply bogus.
- * Give up and tell user space.
- */
- return -ESRCH;
-}
-
-static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
- struct futex_pi_state **ps)
-{
- /*
- * No existing pi state. First waiter. [2]
- *
- * This creates pi_state, we have hb->lock held, this means nothing can
- * observe this state, wait_lock is irrelevant.
- */
- struct futex_pi_state *pi_state = alloc_pi_state();
-
- /*
- * Initialize the pi_mutex in locked state and make @p
- * the owner of it:
- */
- rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
-
- /* Store the key for possible exit cleanups: */
- pi_state->key = *key;
-
- WARN_ON(!list_empty(&pi_state->list));
- list_add(&pi_state->list, &p->pi_state_list);
- /*
- * Assignment without holding pi_state->pi_mutex.wait_lock is safe
- * because there is no concurrency as the object is not published yet.
- */
- pi_state->owner = p;
-
- *ps = pi_state;
-}
-/*
- * Lookup the task for the TID provided from user space and attach to
- * it after doing proper sanity checks.
- */
-static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
- struct futex_pi_state **ps,
- struct task_struct **exiting)
-{
- pid_t pid = uval & FUTEX_TID_MASK;
- struct task_struct *p;
-
- /*
- * We are the first waiter - try to look up the real owner and attach
- * the new pi_state to it, but bail out when TID = 0 [1]
- *
- * The !pid check is paranoid. None of the call sites should end up
- * with pid == 0, but better safe than sorry. Let the caller retry
- */
- if (!pid)
- return -EAGAIN;
- p = find_get_task_by_vpid(pid);
- if (!p)
- return handle_exit_race(uaddr, uval, NULL);
-
- if (unlikely(p->flags & PF_KTHREAD)) {
- put_task_struct(p);
- return -EPERM;
- }
-
- /*
- * We need to look at the task state to figure out, whether the
- * task is exiting. To protect against the change of the task state
- * in futex_exit_release(), we do this protected by p->pi_lock:
- */
- raw_spin_lock_irq(&p->pi_lock);
- if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
- /*
- * The task is on the way out. When the futex state is
- * FUTEX_STATE_DEAD, we know that the task has finished
- * the cleanup:
- */
- int ret = handle_exit_race(uaddr, uval, p);
-
- raw_spin_unlock_irq(&p->pi_lock);
- /*
- * If the owner task is between FUTEX_STATE_EXITING and
- * FUTEX_STATE_DEAD then store the task pointer and keep
- * the reference on the task struct. The calling code will
- * drop all locks, wait for the task to reach
- * FUTEX_STATE_DEAD and then drop the refcount. This is
- * required to prevent a live lock when the current task
- * preempted the exiting task between the two states.
- */
- if (ret == -EBUSY)
- *exiting = p;
- else
- put_task_struct(p);
- return ret;
- }
-
- __attach_to_pi_owner(p, key, ps);
- raw_spin_unlock_irq(&p->pi_lock);
-
- put_task_struct(p);
-
- return 0;
-}
-
-static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
-{
- int err;
- u32 curval;
-
- if (unlikely(should_fail_futex(true)))
- return -EFAULT;
-
- err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
- if (unlikely(err))
- return err;
-
- /* If user space value changed, let the caller retry */
- return curval != uval ? -EAGAIN : 0;
-}
-
-/**
- * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
- * @uaddr: the pi futex user address
- * @hb: the pi futex hash bucket
- * @key: the futex key associated with uaddr and hb
- * @ps: the pi_state pointer where we store the result of the
- * lookup
- * @task: the task to perform the atomic lock work for. This will
- * be "current" except in the case of requeue pi.
- * @exiting: Pointer to store the task pointer of the owner task
- * which is in the middle of exiting
- * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
- *
- * Return:
- * - 0 - ready to wait;
- * - 1 - acquired the lock;
- * - <0 - error
- *
- * The hb->lock must be held by the caller.
- *
- * @exiting is only set when the return value is -EBUSY. If so, this holds
- * a refcount on the exiting task on return and the caller needs to drop it
- * after waiting for the exit to complete.
- */
-static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
- union futex_key *key,
- struct futex_pi_state **ps,
- struct task_struct *task,
- struct task_struct **exiting,
- int set_waiters)
-{
- u32 uval, newval, vpid = task_pid_vnr(task);
- struct futex_q *top_waiter;
- int ret;
-
- /*
- * Read the user space value first so we can validate a few
- * things before proceeding further.
- */
- if (get_futex_value_locked(&uval, uaddr))
- return -EFAULT;
-
- if (unlikely(should_fail_futex(true)))
- return -EFAULT;
-
- /*
- * Detect deadlocks.
- */
- if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
- return -EDEADLK;
-
- if ((unlikely(should_fail_futex(true))))
- return -EDEADLK;
-
- /*
- * Lookup existing state first. If it exists, try to attach to
- * its pi_state.
- */
- top_waiter = futex_top_waiter(hb, key);
- if (top_waiter)
- return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
-
- /*
- * No waiter and user TID is 0. We are here because the
- * waiters or the owner died bit is set or called from
- * requeue_cmp_pi or for whatever reason something took the
- * syscall.
- */
- if (!(uval & FUTEX_TID_MASK)) {
- /*
- * We take over the futex. No other waiters and the user space
- * TID is 0. We preserve the owner died bit.
- */
- newval = uval & FUTEX_OWNER_DIED;
- newval |= vpid;
-
- /* The futex requeue_pi code can enforce the waiters bit */
- if (set_waiters)
- newval |= FUTEX_WAITERS;
-
- ret = lock_pi_update_atomic(uaddr, uval, newval);
- if (ret)
- return ret;
-
- /*
- * If the waiter bit was requested the caller also needs PI
- * state attached to the new owner of the user space futex.
- *
- * @task is guaranteed to be alive and it cannot be exiting
- * because it is either sleeping or waiting in
- * futex_requeue_pi_wakeup_sync().
- *
- * No need to do the full attach_to_pi_owner() exercise
- * because @task is known and valid.
- */
- if (set_waiters) {
- raw_spin_lock_irq(&task->pi_lock);
- __attach_to_pi_owner(task, key, ps);
- raw_spin_unlock_irq(&task->pi_lock);
- }
- return 1;
- }
-
- /*
- * First waiter. Set the waiters bit before attaching ourself to
- * the owner. If owner tries to unlock, it will be forced into
- * the kernel and blocked on hb->lock.
- */
- newval = uval | FUTEX_WAITERS;
- ret = lock_pi_update_atomic(uaddr, uval, newval);
- if (ret)
- return ret;
- /*
- * If the update of the user space value succeeded, we try to
- * attach to the owner. If that fails, no harm done, we only
- * set the FUTEX_WAITERS bit in the user space variable.
- */
- return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
-}
-
-/**
- * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
- * @q: The futex_q to unqueue
- *
- * The q->lock_ptr must not be NULL and must be held by the caller.
- */
-static void __unqueue_futex(struct futex_q *q)
-{
- struct futex_hash_bucket *hb;
-
- if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
- return;
- lockdep_assert_held(q->lock_ptr);
-
- hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
- plist_del(&q->list, &hb->chain);
- hb_waiters_dec(hb);
-}
-
-/*
- * The hash bucket lock must be held when this is called.
- * Afterwards, the futex_q must not be accessed. Callers
- * must ensure to later call wake_up_q() for the actual
- * wakeups to occur.
- */
-static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
-{
- struct task_struct *p = q->task;
-
- if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
- return;
-
- get_task_struct(p);
- __unqueue_futex(q);
- /*
- * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
- * is written, without taking any locks. This is possible in the event
- * of a spurious wakeup, for example. A memory barrier is required here
- * to prevent the following store to lock_ptr from getting ahead of the
- * plist_del in __unqueue_futex().
- */
- smp_store_release(&q->lock_ptr, NULL);
-
- /*
- * Queue the task for later wakeup for after we've released
- * the hb->lock.
- */
- wake_q_add_safe(wake_q, p);
-}
-
-/*
- * Caller must hold a reference on @pi_state.
- */
-static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
-{
- struct rt_mutex_waiter *top_waiter;
- struct task_struct *new_owner;
- bool postunlock = false;
- DEFINE_RT_WAKE_Q(wqh);
- u32 curval, newval;
- int ret = 0;
-
- top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
- if (WARN_ON_ONCE(!top_waiter)) {
- /*
- * As per the comment in futex_unlock_pi() this should not happen.
- *
- * When this happens, give up our locks and try again, giving
- * the futex_lock_pi() instance time to complete, either by
- * waiting on the rtmutex or removing itself from the futex
- * queue.
- */
- ret = -EAGAIN;
- goto out_unlock;
- }
-
- new_owner = top_waiter->task;
-
- /*
- * We pass it to the next owner. The WAITERS bit is always kept
- * enabled while there is PI state around. We cleanup the owner
- * died bit, because we are the owner.
- */
- newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
-
- if (unlikely(should_fail_futex(true))) {
- ret = -EFAULT;
- goto out_unlock;
- }
-
- ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
- if (!ret && (curval != uval)) {
- /*
- * If a unconditional UNLOCK_PI operation (user space did not
- * try the TID->0 transition) raced with a waiter setting the
- * FUTEX_WAITERS flag between get_user() and locking the hash
- * bucket lock, retry the operation.
- */
- if ((FUTEX_TID_MASK & curval) == uval)
- ret = -EAGAIN;
- else
- ret = -EINVAL;
- }
-
- if (!ret) {
- /*
- * This is a point of no return; once we modified the uval
- * there is no going back and subsequent operations must
- * not fail.
- */
- pi_state_update_owner(pi_state, new_owner);
- postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
- }
-
-out_unlock:
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-
- if (postunlock)
- rt_mutex_postunlock(&wqh);
-
- return ret;
-}
-
-/*
- * Express the locking dependencies for lockdep:
- */
-static inline void
-double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
-{
- if (hb1 <= hb2) {
- spin_lock(&hb1->lock);
- if (hb1 < hb2)
- spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
- } else { /* hb1 > hb2 */
- spin_lock(&hb2->lock);
- spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
- }
-}
-
-static inline void
-double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
-{
- spin_unlock(&hb1->lock);
- if (hb1 != hb2)
- spin_unlock(&hb2->lock);
-}
-
-/*
- * Wake up waiters matching bitset queued on this futex (uaddr).
- */
-static int
-futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
-{
- struct futex_hash_bucket *hb;
- struct futex_q *this, *next;
- union futex_key key = FUTEX_KEY_INIT;
- int ret;
- DEFINE_WAKE_Q(wake_q);
-
- if (!bitset)
- return -EINVAL;
-
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
-
- hb = hash_futex(&key);
-
- /* Make sure we really have tasks to wakeup */
- if (!hb_waiters_pending(hb))
- return ret;
-
- spin_lock(&hb->lock);
-
- plist_for_each_entry_safe(this, next, &hb->chain, list) {
- if (match_futex (&this->key, &key)) {
- if (this->pi_state || this->rt_waiter) {
- ret = -EINVAL;
- break;
- }
-
- /* Check if one of the bits is set in both bitsets */
- if (!(this->bitset & bitset))
- continue;
-
- mark_wake_futex(&wake_q, this);
- if (++ret >= nr_wake)
- break;
- }
- }
-
- spin_unlock(&hb->lock);
- wake_up_q(&wake_q);
- return ret;
-}
-
-static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
-{
- unsigned int op = (encoded_op & 0x70000000) >> 28;
- unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
- int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
- int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
- int oldval, ret;
-
- if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
- if (oparg < 0 || oparg > 31) {
- char comm[sizeof(current->comm)];
- /*
- * kill this print and return -EINVAL when userspace
- * is sane again
- */
- pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
- get_task_comm(comm, current), oparg);
- oparg &= 31;
- }
- oparg = 1 << oparg;
- }
-
- pagefault_disable();
- ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
- pagefault_enable();
- if (ret)
- return ret;
-
- switch (cmp) {
- case FUTEX_OP_CMP_EQ:
- return oldval == cmparg;
- case FUTEX_OP_CMP_NE:
- return oldval != cmparg;
- case FUTEX_OP_CMP_LT:
- return oldval < cmparg;
- case FUTEX_OP_CMP_GE:
- return oldval >= cmparg;
- case FUTEX_OP_CMP_LE:
- return oldval <= cmparg;
- case FUTEX_OP_CMP_GT:
- return oldval > cmparg;
- default:
- return -ENOSYS;
- }
-}
-
-/*
- * Wake up all waiters hashed on the physical page that is mapped
- * to this virtual address:
- */
-static int
-futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
- int nr_wake, int nr_wake2, int op)
-{
- union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
- struct futex_hash_bucket *hb1, *hb2;
- struct futex_q *this, *next;
- int ret, op_ret;
- DEFINE_WAKE_Q(wake_q);
-
-retry:
- ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
- ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
- if (unlikely(ret != 0))
- return ret;
-
- hb1 = hash_futex(&key1);
- hb2 = hash_futex(&key2);
-
-retry_private:
- double_lock_hb(hb1, hb2);
- op_ret = futex_atomic_op_inuser(op, uaddr2);
- if (unlikely(op_ret < 0)) {
- double_unlock_hb(hb1, hb2);
-
- if (!IS_ENABLED(CONFIG_MMU) ||
- unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
- /*
- * we don't get EFAULT from MMU faults if we don't have
- * an MMU, but we might get them from range checking
- */
- ret = op_ret;
- return ret;
- }
-
- if (op_ret == -EFAULT) {
- ret = fault_in_user_writeable(uaddr2);
- if (ret)
- return ret;
- }
-
- cond_resched();
- if (!(flags & FLAGS_SHARED))
- goto retry_private;
- goto retry;
- }
-
- plist_for_each_entry_safe(this, next, &hb1->chain, list) {
- if (match_futex (&this->key, &key1)) {
- if (this->pi_state || this->rt_waiter) {
- ret = -EINVAL;
- goto out_unlock;
- }
- mark_wake_futex(&wake_q, this);
- if (++ret >= nr_wake)
- break;
- }
- }
-
- if (op_ret > 0) {
- op_ret = 0;
- plist_for_each_entry_safe(this, next, &hb2->chain, list) {
- if (match_futex (&this->key, &key2)) {
- if (this->pi_state || this->rt_waiter) {
- ret = -EINVAL;
- goto out_unlock;
- }
- mark_wake_futex(&wake_q, this);
- if (++op_ret >= nr_wake2)
- break;
- }
- }
- ret += op_ret;
- }
-
-out_unlock:
- double_unlock_hb(hb1, hb2);
- wake_up_q(&wake_q);
- return ret;
-}
-
-/**
- * requeue_futex() - Requeue a futex_q from one hb to another
- * @q: the futex_q to requeue
- * @hb1: the source hash_bucket
- * @hb2: the target hash_bucket
- * @key2: the new key for the requeued futex_q
- */
-static inline
-void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
- struct futex_hash_bucket *hb2, union futex_key *key2)
-{
-
- /*
- * If key1 and key2 hash to the same bucket, no need to
- * requeue.
- */
- if (likely(&hb1->chain != &hb2->chain)) {
- plist_del(&q->list, &hb1->chain);
- hb_waiters_dec(hb1);
- hb_waiters_inc(hb2);
- plist_add(&q->list, &hb2->chain);
- q->lock_ptr = &hb2->lock;
- }
- q->key = *key2;
-}
-
-static inline bool futex_requeue_pi_prepare(struct futex_q *q,
- struct futex_pi_state *pi_state)
-{
- int old, new;
-
- /*
- * Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has
- * already set Q_REQUEUE_PI_IGNORE to signal that requeue should
- * ignore the waiter.
- */
- old = atomic_read_acquire(&q->requeue_state);
- do {
- if (old == Q_REQUEUE_PI_IGNORE)
- return false;
-
- /*
- * futex_proxy_trylock_atomic() might have set it to
- * IN_PROGRESS and a interleaved early wake to WAIT.
- *
- * It was considered to have an extra state for that
- * trylock, but that would just add more conditionals
- * all over the place for a dubious value.
- */
- if (old != Q_REQUEUE_PI_NONE)
- break;
-
- new = Q_REQUEUE_PI_IN_PROGRESS;
- } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
-
- q->pi_state = pi_state;
- return true;
-}
-
-static inline void futex_requeue_pi_complete(struct futex_q *q, int locked)
-{
- int old, new;
-
- old = atomic_read_acquire(&q->requeue_state);
- do {
- if (old == Q_REQUEUE_PI_IGNORE)
- return;
-
- if (locked >= 0) {
- /* Requeue succeeded. Set DONE or LOCKED */
- WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS &&
- old != Q_REQUEUE_PI_WAIT);
- new = Q_REQUEUE_PI_DONE + locked;
- } else if (old == Q_REQUEUE_PI_IN_PROGRESS) {
- /* Deadlock, no early wakeup interleave */
- new = Q_REQUEUE_PI_NONE;
- } else {
- /* Deadlock, early wakeup interleave. */
- WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT);
- new = Q_REQUEUE_PI_IGNORE;
- }
- } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
-
-#ifdef CONFIG_PREEMPT_RT
- /* If the waiter interleaved with the requeue let it know */
- if (unlikely(old == Q_REQUEUE_PI_WAIT))
- rcuwait_wake_up(&q->requeue_wait);
-#endif
-}
-
-static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
-{
- int old, new;
-
- old = atomic_read_acquire(&q->requeue_state);
- do {
- /* Is requeue done already? */
- if (old >= Q_REQUEUE_PI_DONE)
- return old;
-
- /*
- * If not done, then tell the requeue code to either ignore
- * the waiter or to wake it up once the requeue is done.
- */
- new = Q_REQUEUE_PI_WAIT;
- if (old == Q_REQUEUE_PI_NONE)
- new = Q_REQUEUE_PI_IGNORE;
- } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
-
- /* If the requeue was in progress, wait for it to complete */
- if (old == Q_REQUEUE_PI_IN_PROGRESS) {
-#ifdef CONFIG_PREEMPT_RT
- rcuwait_wait_event(&q->requeue_wait,
- atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT,
- TASK_UNINTERRUPTIBLE);
-#else
- (void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT);
-#endif
- }
-
- /*
- * Requeue is now either prohibited or complete. Reread state
- * because during the wait above it might have changed. Nothing
- * will modify q->requeue_state after this point.
- */
- return atomic_read(&q->requeue_state);
-}
-
-/**
- * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
- * @q: the futex_q
- * @key: the key of the requeue target futex
- * @hb: the hash_bucket of the requeue target futex
- *
- * During futex_requeue, with requeue_pi=1, it is possible to acquire the
- * target futex if it is uncontended or via a lock steal.
- *
- * 1) Set @q::key to the requeue target futex key so the waiter can detect
- * the wakeup on the right futex.
- *
- * 2) Dequeue @q from the hash bucket.
- *
- * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock
- * acquisition.
- *
- * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that
- * the waiter has to fixup the pi state.
- *
- * 5) Complete the requeue state so the waiter can make progress. After
- * this point the waiter task can return from the syscall immediately in
- * case that the pi state does not have to be fixed up.
- *
- * 6) Wake the waiter task.
- *
- * Must be called with both q->lock_ptr and hb->lock held.
- */
-static inline
-void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
- struct futex_hash_bucket *hb)
-{
- q->key = *key;
-
- __unqueue_futex(q);
-
- WARN_ON(!q->rt_waiter);
- q->rt_waiter = NULL;
-
- q->lock_ptr = &hb->lock;
-
- /* Signal locked state to the waiter */
- futex_requeue_pi_complete(q, 1);
- wake_up_state(q->task, TASK_NORMAL);
-}
-
-/**
- * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
- * @pifutex: the user address of the to futex
- * @hb1: the from futex hash bucket, must be locked by the caller
- * @hb2: the to futex hash bucket, must be locked by the caller
- * @key1: the from futex key
- * @key2: the to futex key
- * @ps: address to store the pi_state pointer
- * @exiting: Pointer to store the task pointer of the owner task
- * which is in the middle of exiting
- * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
- *
- * Try and get the lock on behalf of the top waiter if we can do it atomically.
- * Wake the top waiter if we succeed. If the caller specified set_waiters,
- * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
- * hb1 and hb2 must be held by the caller.
- *
- * @exiting is only set when the return value is -EBUSY. If so, this holds
- * a refcount on the exiting task on return and the caller needs to drop it
- * after waiting for the exit to complete.
- *
- * Return:
- * - 0 - failed to acquire the lock atomically;
- * - >0 - acquired the lock, return value is vpid of the top_waiter
- * - <0 - error
- */
-static int
-futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
- struct futex_hash_bucket *hb2, union futex_key *key1,
- union futex_key *key2, struct futex_pi_state **ps,
- struct task_struct **exiting, int set_waiters)
-{
- struct futex_q *top_waiter = NULL;
- u32 curval;
- int ret;
-
- if (get_futex_value_locked(&curval, pifutex))
- return -EFAULT;
-
- if (unlikely(should_fail_futex(true)))
- return -EFAULT;
-
- /*
- * Find the top_waiter and determine if there are additional waiters.
- * If the caller intends to requeue more than 1 waiter to pifutex,
- * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
- * as we have means to handle the possible fault. If not, don't set
- * the bit unnecessarily as it will force the subsequent unlock to enter
- * the kernel.
- */
- top_waiter = futex_top_waiter(hb1, key1);
-
- /* There are no waiters, nothing for us to do. */
- if (!top_waiter)
- return 0;
-
- /*
- * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
- * and waiting on the 'waitqueue' futex which is always !PI.
- */
- if (!top_waiter->rt_waiter || top_waiter->pi_state)
- return -EINVAL;
-
- /* Ensure we requeue to the expected futex. */
- if (!match_futex(top_waiter->requeue_pi_key, key2))
- return -EINVAL;
-
- /* Ensure that this does not race against an early wakeup */
- if (!futex_requeue_pi_prepare(top_waiter, NULL))
- return -EAGAIN;
-
- /*
- * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
- * in the contended case or if @set_waiters is true.
- *
- * In the contended case PI state is attached to the lock owner. If
- * the user space lock can be acquired then PI state is attached to
- * the new owner (@top_waiter->task) when @set_waiters is true.
- */
- ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
- exiting, set_waiters);
- if (ret == 1) {
- /*
- * Lock was acquired in user space and PI state was
- * attached to @top_waiter->task. That means state is fully
- * consistent and the waiter can return to user space
- * immediately after the wakeup.
- */
- requeue_pi_wake_futex(top_waiter, key2, hb2);
- } else if (ret < 0) {
- /* Rewind top_waiter::requeue_state */
- futex_requeue_pi_complete(top_waiter, ret);
- } else {
- /*
- * futex_lock_pi_atomic() did not acquire the user space
- * futex, but managed to establish the proxy lock and pi
- * state. top_waiter::requeue_state cannot be fixed up here
- * because the waiter is not enqueued on the rtmutex
- * yet. This is handled at the callsite depending on the
- * result of rt_mutex_start_proxy_lock() which is
- * guaranteed to be reached with this function returning 0.
- */
- }
- return ret;
-}
-
-/**
- * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
- * @uaddr1: source futex user address
- * @flags: futex flags (FLAGS_SHARED, etc.)
- * @uaddr2: target futex user address
- * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
- * @nr_requeue: number of waiters to requeue (0-INT_MAX)
- * @cmpval: @uaddr1 expected value (or %NULL)
- * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
- * pi futex (pi to pi requeue is not supported)
- *
- * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
- * uaddr2 atomically on behalf of the top waiter.
- *
- * Return:
- * - >=0 - on success, the number of tasks requeued or woken;
- * - <0 - on error
- */
-static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
- u32 __user *uaddr2, int nr_wake, int nr_requeue,
- u32 *cmpval, int requeue_pi)
-{
- union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
- int task_count = 0, ret;
- struct futex_pi_state *pi_state = NULL;
- struct futex_hash_bucket *hb1, *hb2;
- struct futex_q *this, *next;
- DEFINE_WAKE_Q(wake_q);
-
- if (nr_wake < 0 || nr_requeue < 0)
- return -EINVAL;
-
- /*
- * When PI not supported: return -ENOSYS if requeue_pi is true,
- * consequently the compiler knows requeue_pi is always false past
- * this point which will optimize away all the conditional code
- * further down.
- */
- if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
- return -ENOSYS;
-
- if (requeue_pi) {
- /*
- * Requeue PI only works on two distinct uaddrs. This
- * check is only valid for private futexes. See below.
- */
- if (uaddr1 == uaddr2)
- return -EINVAL;
-
- /*
- * futex_requeue() allows the caller to define the number
- * of waiters to wake up via the @nr_wake argument. With
- * REQUEUE_PI, waking up more than one waiter is creating
- * more problems than it solves. Waking up a waiter makes
- * only sense if the PI futex @uaddr2 is uncontended as
- * this allows the requeue code to acquire the futex
- * @uaddr2 before waking the waiter. The waiter can then
- * return to user space without further action. A secondary
- * wakeup would just make the futex_wait_requeue_pi()
- * handling more complex, because that code would have to
- * look up pi_state and do more or less all the handling
- * which the requeue code has to do for the to be requeued
- * waiters. So restrict the number of waiters to wake to
- * one, and only wake it up when the PI futex is
- * uncontended. Otherwise requeue it and let the unlock of
- * the PI futex handle the wakeup.
- *
- * All REQUEUE_PI users, e.g. pthread_cond_signal() and
- * pthread_cond_broadcast() must use nr_wake=1.
- */
- if (nr_wake != 1)
- return -EINVAL;
-
- /*
- * requeue_pi requires a pi_state, try to allocate it now
- * without any locks in case it fails.
- */
- if (refill_pi_state_cache())
- return -ENOMEM;
- }
-
-retry:
- ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
- ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
- requeue_pi ? FUTEX_WRITE : FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
-
- /*
- * The check above which compares uaddrs is not sufficient for
- * shared futexes. We need to compare the keys:
- */
- if (requeue_pi && match_futex(&key1, &key2))
- return -EINVAL;
-
- hb1 = hash_futex(&key1);
- hb2 = hash_futex(&key2);
-
-retry_private:
- hb_waiters_inc(hb2);
- double_lock_hb(hb1, hb2);
-
- if (likely(cmpval != NULL)) {
- u32 curval;
-
- ret = get_futex_value_locked(&curval, uaddr1);
-
- if (unlikely(ret)) {
- double_unlock_hb(hb1, hb2);
- hb_waiters_dec(hb2);
-
- ret = get_user(curval, uaddr1);
- if (ret)
- return ret;
-
- if (!(flags & FLAGS_SHARED))
- goto retry_private;
-
- goto retry;
- }
- if (curval != *cmpval) {
- ret = -EAGAIN;
- goto out_unlock;
- }
- }
-
- if (requeue_pi) {
- struct task_struct *exiting = NULL;
-
- /*
- * Attempt to acquire uaddr2 and wake the top waiter. If we
- * intend to requeue waiters, force setting the FUTEX_WAITERS
- * bit. We force this here where we are able to easily handle
- * faults rather in the requeue loop below.
- *
- * Updates topwaiter::requeue_state if a top waiter exists.
- */
- ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
- &key2, &pi_state,
- &exiting, nr_requeue);
-
- /*
- * At this point the top_waiter has either taken uaddr2 or
- * is waiting on it. In both cases pi_state has been
- * established and an initial refcount on it. In case of an
- * error there's nothing.
- *
- * The top waiter's requeue_state is up to date:
- *
- * - If the lock was acquired atomically (ret == 1), then
- * the state is Q_REQUEUE_PI_LOCKED.
- *
- * The top waiter has been dequeued and woken up and can
- * return to user space immediately. The kernel/user
- * space state is consistent. In case that there must be
- * more waiters requeued the WAITERS bit in the user
- * space futex is set so the top waiter task has to go
- * into the syscall slowpath to unlock the futex. This
- * will block until this requeue operation has been
- * completed and the hash bucket locks have been
- * dropped.
- *
- * - If the trylock failed with an error (ret < 0) then
- * the state is either Q_REQUEUE_PI_NONE, i.e. "nothing
- * happened", or Q_REQUEUE_PI_IGNORE when there was an
- * interleaved early wakeup.
- *
- * - If the trylock did not succeed (ret == 0) then the
- * state is either Q_REQUEUE_PI_IN_PROGRESS or
- * Q_REQUEUE_PI_WAIT if an early wakeup interleaved.
- * This will be cleaned up in the loop below, which
- * cannot fail because futex_proxy_trylock_atomic() did
- * the same sanity checks for requeue_pi as the loop
- * below does.
- */
- switch (ret) {
- case 0:
- /* We hold a reference on the pi state. */
- break;
-
- case 1:
- /*
- * futex_proxy_trylock_atomic() acquired the user space
- * futex. Adjust task_count.
- */
- task_count++;
- ret = 0;
- break;
-
- /*
- * If the above failed, then pi_state is NULL and
- * waiter::requeue_state is correct.
- */
- case -EFAULT:
- double_unlock_hb(hb1, hb2);
- hb_waiters_dec(hb2);
- ret = fault_in_user_writeable(uaddr2);
- if (!ret)
- goto retry;
- return ret;
- case -EBUSY:
- case -EAGAIN:
- /*
- * Two reasons for this:
- * - EBUSY: Owner is exiting and we just wait for the
- * exit to complete.
- * - EAGAIN: The user space value changed.
- */
- double_unlock_hb(hb1, hb2);
- hb_waiters_dec(hb2);
- /*
- * Handle the case where the owner is in the middle of
- * exiting. Wait for the exit to complete otherwise
- * this task might loop forever, aka. live lock.
- */
- wait_for_owner_exiting(ret, exiting);
- cond_resched();
- goto retry;
- default:
- goto out_unlock;
- }
- }
-
- plist_for_each_entry_safe(this, next, &hb1->chain, list) {
- if (task_count - nr_wake >= nr_requeue)
- break;
-
- if (!match_futex(&this->key, &key1))
- continue;
-
- /*
- * FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always
- * be paired with each other and no other futex ops.
- *
- * We should never be requeueing a futex_q with a pi_state,
- * which is awaiting a futex_unlock_pi().
- */
- if ((requeue_pi && !this->rt_waiter) ||
- (!requeue_pi && this->rt_waiter) ||
- this->pi_state) {
- ret = -EINVAL;
- break;
- }
-
- /* Plain futexes just wake or requeue and are done */
- if (!requeue_pi) {
- if (++task_count <= nr_wake)
- mark_wake_futex(&wake_q, this);
- else
- requeue_futex(this, hb1, hb2, &key2);
- continue;
- }
-
- /* Ensure we requeue to the expected futex for requeue_pi. */
- if (!match_futex(this->requeue_pi_key, &key2)) {
- ret = -EINVAL;
- break;
- }
-
- /*
- * Requeue nr_requeue waiters and possibly one more in the case
- * of requeue_pi if we couldn't acquire the lock atomically.
- *
- * Prepare the waiter to take the rt_mutex. Take a refcount
- * on the pi_state and store the pointer in the futex_q
- * object of the waiter.
- */
- get_pi_state(pi_state);
-
- /* Don't requeue when the waiter is already on the way out. */
- if (!futex_requeue_pi_prepare(this, pi_state)) {
- /*
- * Early woken waiter signaled that it is on the
- * way out. Drop the pi_state reference and try the
- * next waiter. @this->pi_state is still NULL.
- */
- put_pi_state(pi_state);
- continue;
- }
-
- ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
- this->rt_waiter,
- this->task);
-
- if (ret == 1) {
- /*
- * We got the lock. We do neither drop the refcount
- * on pi_state nor clear this->pi_state because the
- * waiter needs the pi_state for cleaning up the
- * user space value. It will drop the refcount
- * after doing so. this::requeue_state is updated
- * in the wakeup as well.
- */
- requeue_pi_wake_futex(this, &key2, hb2);
- task_count++;
- } else if (!ret) {
- /* Waiter is queued, move it to hb2 */
- requeue_futex(this, hb1, hb2, &key2);
- futex_requeue_pi_complete(this, 0);
- task_count++;
- } else {
- /*
- * rt_mutex_start_proxy_lock() detected a potential
- * deadlock when we tried to queue that waiter.
- * Drop the pi_state reference which we took above
- * and remove the pointer to the state from the
- * waiters futex_q object.
- */
- this->pi_state = NULL;
- put_pi_state(pi_state);
- futex_requeue_pi_complete(this, ret);
- /*
- * We stop queueing more waiters and let user space
- * deal with the mess.
- */
- break;
- }
- }
-
- /*
- * We took an extra initial reference to the pi_state in
- * futex_proxy_trylock_atomic(). We need to drop it here again.
- */
- put_pi_state(pi_state);
-
-out_unlock:
- double_unlock_hb(hb1, hb2);
- wake_up_q(&wake_q);
- hb_waiters_dec(hb2);
- return ret ? ret : task_count;
-}
-
-/* The key must be already stored in q->key. */
-static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
- __acquires(&hb->lock)
-{
- struct futex_hash_bucket *hb;
-
- hb = hash_futex(&q->key);
-
- /*
- * Increment the counter before taking the lock so that
- * a potential waker won't miss a to-be-slept task that is
- * waiting for the spinlock. This is safe as all queue_lock()
- * users end up calling queue_me(). Similarly, for housekeeping,
- * decrement the counter at queue_unlock() when some error has
- * occurred and we don't end up adding the task to the list.
- */
- hb_waiters_inc(hb); /* implies smp_mb(); (A) */
-
- q->lock_ptr = &hb->lock;
-
- spin_lock(&hb->lock);
- return hb;
-}
-
-static inline void
-queue_unlock(struct futex_hash_bucket *hb)
- __releases(&hb->lock)
-{
- spin_unlock(&hb->lock);
- hb_waiters_dec(hb);
-}
-
-static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
-{
- int prio;
-
- /*
- * The priority used to register this element is
- * - either the real thread-priority for the real-time threads
- * (i.e. threads with a priority lower than MAX_RT_PRIO)
- * - or MAX_RT_PRIO for non-RT threads.
- * Thus, all RT-threads are woken first in priority order, and
- * the others are woken last, in FIFO order.
- */
- prio = min(current->normal_prio, MAX_RT_PRIO);
-
- plist_node_init(&q->list, prio);
- plist_add(&q->list, &hb->chain);
- q->task = current;
-}
-
-/**
- * queue_me() - Enqueue the futex_q on the futex_hash_bucket
- * @q: The futex_q to enqueue
- * @hb: The destination hash bucket
- *
- * The hb->lock must be held by the caller, and is released here. A call to
- * queue_me() is typically paired with exactly one call to unqueue_me(). The
- * exceptions involve the PI related operations, which may use unqueue_me_pi()
- * or nothing if the unqueue is done as part of the wake process and the unqueue
- * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
- * an example).
- */
-static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
- __releases(&hb->lock)
-{
- __queue_me(q, hb);
- spin_unlock(&hb->lock);
-}
-
-/**
- * unqueue_me() - Remove the futex_q from its futex_hash_bucket
- * @q: The futex_q to unqueue
- *
- * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
- * be paired with exactly one earlier call to queue_me().
- *
- * Return:
- * - 1 - if the futex_q was still queued (and we removed unqueued it);
- * - 0 - if the futex_q was already removed by the waking thread
- */
-static int unqueue_me(struct futex_q *q)
-{
- spinlock_t *lock_ptr;
- int ret = 0;
-
- /* In the common case we don't take the spinlock, which is nice. */
-retry:
- /*
- * q->lock_ptr can change between this read and the following spin_lock.
- * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
- * optimizing lock_ptr out of the logic below.
- */
- lock_ptr = READ_ONCE(q->lock_ptr);
- if (lock_ptr != NULL) {
- spin_lock(lock_ptr);
- /*
- * q->lock_ptr can change between reading it and
- * spin_lock(), causing us to take the wrong lock. This
- * corrects the race condition.
- *
- * Reasoning goes like this: if we have the wrong lock,
- * q->lock_ptr must have changed (maybe several times)
- * between reading it and the spin_lock(). It can
- * change again after the spin_lock() but only if it was
- * already changed before the spin_lock(). It cannot,
- * however, change back to the original value. Therefore
- * we can detect whether we acquired the correct lock.
- */
- if (unlikely(lock_ptr != q->lock_ptr)) {
- spin_unlock(lock_ptr);
- goto retry;
- }
- __unqueue_futex(q);
-
- BUG_ON(q->pi_state);
-
- spin_unlock(lock_ptr);
- ret = 1;
- }
-
- return ret;
-}
-
-/*
- * PI futexes can not be requeued and must remove themselves from the
- * hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
- */
-static void unqueue_me_pi(struct futex_q *q)
-{
- __unqueue_futex(q);
-
- BUG_ON(!q->pi_state);
- put_pi_state(q->pi_state);
- q->pi_state = NULL;
-}
-
-static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
- struct task_struct *argowner)
-{
- struct futex_pi_state *pi_state = q->pi_state;
- struct task_struct *oldowner, *newowner;
- u32 uval, curval, newval, newtid;
- int err = 0;
-
- oldowner = pi_state->owner;
-
- /*
- * We are here because either:
- *
- * - we stole the lock and pi_state->owner needs updating to reflect
- * that (@argowner == current),
- *
- * or:
- *
- * - someone stole our lock and we need to fix things to point to the
- * new owner (@argowner == NULL).
- *
- * Either way, we have to replace the TID in the user space variable.
- * This must be atomic as we have to preserve the owner died bit here.
- *
- * Note: We write the user space value _before_ changing the pi_state
- * because we can fault here. Imagine swapped out pages or a fork
- * that marked all the anonymous memory readonly for cow.
- *
- * Modifying pi_state _before_ the user space value would leave the
- * pi_state in an inconsistent state when we fault here, because we
- * need to drop the locks to handle the fault. This might be observed
- * in the PID checks when attaching to PI state .
- */
-retry:
- if (!argowner) {
- if (oldowner != current) {
- /*
- * We raced against a concurrent self; things are
- * already fixed up. Nothing to do.
- */
- return 0;
- }
-
- if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
- /* We got the lock. pi_state is correct. Tell caller. */
- return 1;
- }
-
- /*
- * The trylock just failed, so either there is an owner or
- * there is a higher priority waiter than this one.
- */
- newowner = rt_mutex_owner(&pi_state->pi_mutex);
- /*
- * If the higher priority waiter has not yet taken over the
- * rtmutex then newowner is NULL. We can't return here with
- * that state because it's inconsistent vs. the user space
- * state. So drop the locks and try again. It's a valid
- * situation and not any different from the other retry
- * conditions.
- */
- if (unlikely(!newowner)) {
- err = -EAGAIN;
- goto handle_err;
- }
- } else {
- WARN_ON_ONCE(argowner != current);
- if (oldowner == current) {
- /*
- * We raced against a concurrent self; things are
- * already fixed up. Nothing to do.
- */
- return 1;
- }
- newowner = argowner;
- }
-
- newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
- /* Owner died? */
- if (!pi_state->owner)
- newtid |= FUTEX_OWNER_DIED;
-
- err = get_futex_value_locked(&uval, uaddr);
- if (err)
- goto handle_err;
-
- for (;;) {
- newval = (uval & FUTEX_OWNER_DIED) | newtid;
-
- err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
- if (err)
- goto handle_err;
-
- if (curval == uval)
- break;
- uval = curval;
- }
-
- /*
- * We fixed up user space. Now we need to fix the pi_state
- * itself.
- */
- pi_state_update_owner(pi_state, newowner);
-
- return argowner == current;
-
- /*
- * In order to reschedule or handle a page fault, we need to drop the
- * locks here. In the case of a fault, this gives the other task
- * (either the highest priority waiter itself or the task which stole
- * the rtmutex) the chance to try the fixup of the pi_state. So once we
- * are back from handling the fault we need to check the pi_state after
- * reacquiring the locks and before trying to do another fixup. When
- * the fixup has been done already we simply return.
- *
- * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
- * drop hb->lock since the caller owns the hb -> futex_q relation.
- * Dropping the pi_mutex->wait_lock requires the state revalidate.
- */
-handle_err:
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- spin_unlock(q->lock_ptr);
-
- switch (err) {
- case -EFAULT:
- err = fault_in_user_writeable(uaddr);
- break;
-
- case -EAGAIN:
- cond_resched();
- err = 0;
- break;
-
- default:
- WARN_ON_ONCE(1);
- break;
- }
-
- spin_lock(q->lock_ptr);
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
- /*
- * Check if someone else fixed it for us:
- */
- if (pi_state->owner != oldowner)
- return argowner == current;
-
- /* Retry if err was -EAGAIN or the fault in succeeded */
- if (!err)
- goto retry;
-
- /*
- * fault_in_user_writeable() failed so user state is immutable. At
- * best we can make the kernel state consistent but user state will
- * be most likely hosed and any subsequent unlock operation will be
- * rejected due to PI futex rule [10].
- *
- * Ensure that the rtmutex owner is also the pi_state owner despite
- * the user space value claiming something different. There is no
- * point in unlocking the rtmutex if current is the owner as it
- * would need to wait until the next waiter has taken the rtmutex
- * to guarantee consistent state. Keep it simple. Userspace asked
- * for this wreckaged state.
- *
- * The rtmutex has an owner - either current or some other
- * task. See the EAGAIN loop above.
- */
- pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
-
- return err;
-}
-
-static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
- struct task_struct *argowner)
-{
- struct futex_pi_state *pi_state = q->pi_state;
- int ret;
-
- lockdep_assert_held(q->lock_ptr);
-
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
- ret = __fixup_pi_state_owner(uaddr, q, argowner);
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- return ret;
-}
-
-static long futex_wait_restart(struct restart_block *restart);
-
-/**
- * fixup_owner() - Post lock pi_state and corner case management
- * @uaddr: user address of the futex
- * @q: futex_q (contains pi_state and access to the rt_mutex)
- * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
- *
- * After attempting to lock an rt_mutex, this function is called to cleanup
- * the pi_state owner as well as handle race conditions that may allow us to
- * acquire the lock. Must be called with the hb lock held.
- *
- * Return:
- * - 1 - success, lock taken;
- * - 0 - success, lock not taken;
- * - <0 - on error (-EFAULT)
- */
-static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
-{
- if (locked) {
- /*
- * Got the lock. We might not be the anticipated owner if we
- * did a lock-steal - fix up the PI-state in that case:
- *
- * Speculative pi_state->owner read (we don't hold wait_lock);
- * since we own the lock pi_state->owner == current is the
- * stable state, anything else needs more attention.
- */
- if (q->pi_state->owner != current)
- return fixup_pi_state_owner(uaddr, q, current);
- return 1;
- }
-
- /*
- * If we didn't get the lock; check if anybody stole it from us. In
- * that case, we need to fix up the uval to point to them instead of
- * us, otherwise bad things happen. [10]
- *
- * Another speculative read; pi_state->owner == current is unstable
- * but needs our attention.
- */
- if (q->pi_state->owner == current)
- return fixup_pi_state_owner(uaddr, q, NULL);
-
- /*
- * Paranoia check. If we did not take the lock, then we should not be
- * the owner of the rt_mutex. Warn and establish consistent state.
- */
- if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
- return fixup_pi_state_owner(uaddr, q, current);
-
- return 0;
-}
-
-/**
- * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
- * @hb: the futex hash bucket, must be locked by the caller
- * @q: the futex_q to queue up on
- * @timeout: the prepared hrtimer_sleeper, or null for no timeout
- */
-static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
- struct hrtimer_sleeper *timeout)
-{
- /*
- * The task state is guaranteed to be set before another task can
- * wake it. set_current_state() is implemented using smp_store_mb() and
- * queue_me() calls spin_unlock() upon completion, both serializing
- * access to the hash list and forcing another memory barrier.
- */
- set_current_state(TASK_INTERRUPTIBLE);
- queue_me(q, hb);
-
- /* Arm the timer */
- if (timeout)
- hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
-
- /*
- * If we have been removed from the hash list, then another task
- * has tried to wake us, and we can skip the call to schedule().
- */
- if (likely(!plist_node_empty(&q->list))) {
- /*
- * If the timer has already expired, current will already be
- * flagged for rescheduling. Only call schedule if there
- * is no timeout, or if it has yet to expire.
- */
- if (!timeout || timeout->task)
- freezable_schedule();
- }
- __set_current_state(TASK_RUNNING);
-}
-
-/**
- * futex_wait_setup() - Prepare to wait on a futex
- * @uaddr: the futex userspace address
- * @val: the expected value
- * @flags: futex flags (FLAGS_SHARED, etc.)
- * @q: the associated futex_q
- * @hb: storage for hash_bucket pointer to be returned to caller
- *
- * Setup the futex_q and locate the hash_bucket. Get the futex value and
- * compare it with the expected value. Handle atomic faults internally.
- * Return with the hb lock held on success, and unlocked on failure.
- *
- * Return:
- * - 0 - uaddr contains val and hb has been locked;
- * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
- */
-static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
- struct futex_q *q, struct futex_hash_bucket **hb)
-{
- u32 uval;
- int ret;
-
- /*
- * Access the page AFTER the hash-bucket is locked.
- * Order is important:
- *
- * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
- * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
- *
- * The basic logical guarantee of a futex is that it blocks ONLY
- * if cond(var) is known to be true at the time of blocking, for
- * any cond. If we locked the hash-bucket after testing *uaddr, that
- * would open a race condition where we could block indefinitely with
- * cond(var) false, which would violate the guarantee.
- *
- * On the other hand, we insert q and release the hash-bucket only
- * after testing *uaddr. This guarantees that futex_wait() will NOT
- * absorb a wakeup if *uaddr does not match the desired values
- * while the syscall executes.
- */
-retry:
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
- if (unlikely(ret != 0))
- return ret;
-
-retry_private:
- *hb = queue_lock(q);
-
- ret = get_futex_value_locked(&uval, uaddr);
-
- if (ret) {
- queue_unlock(*hb);
-
- ret = get_user(uval, uaddr);
- if (ret)
- return ret;
-
- if (!(flags & FLAGS_SHARED))
- goto retry_private;
-
- goto retry;
- }
-
- if (uval != val) {
- queue_unlock(*hb);
- ret = -EWOULDBLOCK;
- }
-
- return ret;
-}
-
-static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
- ktime_t *abs_time, u32 bitset)
-{
- struct hrtimer_sleeper timeout, *to;
- struct restart_block *restart;
- struct futex_hash_bucket *hb;
- struct futex_q q = futex_q_init;
- int ret;
-
- if (!bitset)
- return -EINVAL;
- q.bitset = bitset;
-
- to = futex_setup_timer(abs_time, &timeout, flags,
- current->timer_slack_ns);
-retry:
- /*
- * Prepare to wait on uaddr. On success, it holds hb->lock and q
- * is initialized.
- */
- ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
- if (ret)
- goto out;
-
- /* queue_me and wait for wakeup, timeout, or a signal. */
- futex_wait_queue_me(hb, &q, to);
-
- /* If we were woken (and unqueued), we succeeded, whatever. */
- ret = 0;
- if (!unqueue_me(&q))
- goto out;
- ret = -ETIMEDOUT;
- if (to && !to->task)
- goto out;
-
- /*
- * We expect signal_pending(current), but we might be the
- * victim of a spurious wakeup as well.
- */
- if (!signal_pending(current))
- goto retry;
-
- ret = -ERESTARTSYS;
- if (!abs_time)
- goto out;
-
- restart = ¤t->restart_block;
- restart->futex.uaddr = uaddr;
- restart->futex.val = val;
- restart->futex.time = *abs_time;
- restart->futex.bitset = bitset;
- restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
-
- ret = set_restart_fn(restart, futex_wait_restart);
-
-out:
- if (to) {
- hrtimer_cancel(&to->timer);
- destroy_hrtimer_on_stack(&to->timer);
- }
- return ret;
-}
-
-
-static long futex_wait_restart(struct restart_block *restart)
-{
- u32 __user *uaddr = restart->futex.uaddr;
- ktime_t t, *tp = NULL;
-
- if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
- t = restart->futex.time;
- tp = &t;
- }
- restart->fn = do_no_restart_syscall;
-
- return (long)futex_wait(uaddr, restart->futex.flags,
- restart->futex.val, tp, restart->futex.bitset);
-}
-
-
-/*
- * Userspace tried a 0 -> TID atomic transition of the futex value
- * and failed. The kernel side here does the whole locking operation:
- * if there are waiters then it will block as a consequence of relying
- * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
- * a 0 value of the futex too.).
- *
- * Also serves as futex trylock_pi()'ing, and due semantics.
- */
-static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
- ktime_t *time, int trylock)
-{
- struct hrtimer_sleeper timeout, *to;
- struct task_struct *exiting = NULL;
- struct rt_mutex_waiter rt_waiter;
- struct futex_hash_bucket *hb;
- struct futex_q q = futex_q_init;
- int res, ret;
-
- if (!IS_ENABLED(CONFIG_FUTEX_PI))
- return -ENOSYS;
-
- if (refill_pi_state_cache())
- return -ENOMEM;
-
- to = futex_setup_timer(time, &timeout, flags, 0);
-
-retry:
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
- if (unlikely(ret != 0))
- goto out;
-
-retry_private:
- hb = queue_lock(&q);
-
- ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
- &exiting, 0);
- if (unlikely(ret)) {
- /*
- * Atomic work succeeded and we got the lock,
- * or failed. Either way, we do _not_ block.
- */
- switch (ret) {
- case 1:
- /* We got the lock. */
- ret = 0;
- goto out_unlock_put_key;
- case -EFAULT:
- goto uaddr_faulted;
- case -EBUSY:
- case -EAGAIN:
- /*
- * Two reasons for this:
- * - EBUSY: Task is exiting and we just wait for the
- * exit to complete.
- * - EAGAIN: The user space value changed.
- */
- queue_unlock(hb);
- /*
- * Handle the case where the owner is in the middle of
- * exiting. Wait for the exit to complete otherwise
- * this task might loop forever, aka. live lock.
- */
- wait_for_owner_exiting(ret, exiting);
- cond_resched();
- goto retry;
- default:
- goto out_unlock_put_key;
- }
- }
-
- WARN_ON(!q.pi_state);
-
- /*
- * Only actually queue now that the atomic ops are done:
- */
- __queue_me(&q, hb);
-
- if (trylock) {
- ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
- /* Fixup the trylock return value: */
- ret = ret ? 0 : -EWOULDBLOCK;
- goto no_block;
- }
-
- rt_mutex_init_waiter(&rt_waiter);
-
- /*
- * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
- * hold it while doing rt_mutex_start_proxy(), because then it will
- * include hb->lock in the blocking chain, even through we'll not in
- * fact hold it while blocking. This will lead it to report -EDEADLK
- * and BUG when futex_unlock_pi() interleaves with this.
- *
- * Therefore acquire wait_lock while holding hb->lock, but drop the
- * latter before calling __rt_mutex_start_proxy_lock(). This
- * interleaves with futex_unlock_pi() -- which does a similar lock
- * handoff -- such that the latter can observe the futex_q::pi_state
- * before __rt_mutex_start_proxy_lock() is done.
- */
- raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
- spin_unlock(q.lock_ptr);
- /*
- * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
- * such that futex_unlock_pi() is guaranteed to observe the waiter when
- * it sees the futex_q::pi_state.
- */
- ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
- raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
-
- if (ret) {
- if (ret == 1)
- ret = 0;
- goto cleanup;
- }
-
- if (unlikely(to))
- hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
-
- ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
-
-cleanup:
- spin_lock(q.lock_ptr);
- /*
- * If we failed to acquire the lock (deadlock/signal/timeout), we must
- * first acquire the hb->lock before removing the lock from the
- * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
- * lists consistent.
- *
- * In particular; it is important that futex_unlock_pi() can not
- * observe this inconsistency.
- */
- if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
- ret = 0;
-
-no_block:
- /*
- * Fixup the pi_state owner and possibly acquire the lock if we
- * haven't already.
- */
- res = fixup_owner(uaddr, &q, !ret);
- /*
- * If fixup_owner() returned an error, propagate that. If it acquired
- * the lock, clear our -ETIMEDOUT or -EINTR.
- */
- if (res)
- ret = (res < 0) ? res : 0;
-
- unqueue_me_pi(&q);
- spin_unlock(q.lock_ptr);
- goto out;
-
-out_unlock_put_key:
- queue_unlock(hb);
-
-out:
- if (to) {
- hrtimer_cancel(&to->timer);
- destroy_hrtimer_on_stack(&to->timer);
- }
- return ret != -EINTR ? ret : -ERESTARTNOINTR;
-
-uaddr_faulted:
- queue_unlock(hb);
-
- ret = fault_in_user_writeable(uaddr);
- if (ret)
- goto out;
-
- if (!(flags & FLAGS_SHARED))
- goto retry_private;
-
- goto retry;
-}
-
-/*
- * Userspace attempted a TID -> 0 atomic transition, and failed.
- * This is the in-kernel slowpath: we look up the PI state (if any),
- * and do the rt-mutex unlock.
- */
-static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
-{
- u32 curval, uval, vpid = task_pid_vnr(current);
- union futex_key key = FUTEX_KEY_INIT;
- struct futex_hash_bucket *hb;
- struct futex_q *top_waiter;
- int ret;
-
- if (!IS_ENABLED(CONFIG_FUTEX_PI))
- return -ENOSYS;
-
-retry:
- if (get_user(uval, uaddr))
- return -EFAULT;
- /*
- * We release only a lock we actually own:
- */
- if ((uval & FUTEX_TID_MASK) != vpid)
- return -EPERM;
-
- ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
- if (ret)
- return ret;
-
- hb = hash_futex(&key);
- spin_lock(&hb->lock);
-
- /*
- * Check waiters first. We do not trust user space values at
- * all and we at least want to know if user space fiddled
- * with the futex value instead of blindly unlocking.
- */
- top_waiter = futex_top_waiter(hb, &key);
- if (top_waiter) {
- struct futex_pi_state *pi_state = top_waiter->pi_state;
-
- ret = -EINVAL;
- if (!pi_state)
- goto out_unlock;
-
- /*
- * If current does not own the pi_state then the futex is
- * inconsistent and user space fiddled with the futex value.
- */
- if (pi_state->owner != current)
- goto out_unlock;
-
- get_pi_state(pi_state);
- /*
- * By taking wait_lock while still holding hb->lock, we ensure
- * there is no point where we hold neither; and therefore
- * wake_futex_pi() must observe a state consistent with what we
- * observed.
- *
- * In particular; this forces __rt_mutex_start_proxy() to
- * complete such that we're guaranteed to observe the
- * rt_waiter. Also see the WARN in wake_futex_pi().
- */
- raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
- spin_unlock(&hb->lock);
-
- /* drops pi_state->pi_mutex.wait_lock */
- ret = wake_futex_pi(uaddr, uval, pi_state);
-
- put_pi_state(pi_state);
-
- /*
- * Success, we're done! No tricky corner cases.
- */
- if (!ret)
- return ret;
- /*
- * The atomic access to the futex value generated a
- * pagefault, so retry the user-access and the wakeup:
- */
- if (ret == -EFAULT)
- goto pi_faulted;
- /*
- * A unconditional UNLOCK_PI op raced against a waiter
- * setting the FUTEX_WAITERS bit. Try again.
- */
- if (ret == -EAGAIN)
- goto pi_retry;
- /*
- * wake_futex_pi has detected invalid state. Tell user
- * space.
- */
- return ret;
- }
-
- /*
- * We have no kernel internal state, i.e. no waiters in the
- * kernel. Waiters which are about to queue themselves are stuck
- * on hb->lock. So we can safely ignore them. We do neither
- * preserve the WAITERS bit not the OWNER_DIED one. We are the
- * owner.
- */
- if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
- spin_unlock(&hb->lock);
- switch (ret) {
- case -EFAULT:
- goto pi_faulted;
-
- case -EAGAIN:
- goto pi_retry;
-
- default:
- WARN_ON_ONCE(1);
- return ret;
- }
- }
-
- /*
- * If uval has changed, let user space handle it.
- */
- ret = (curval == uval) ? 0 : -EAGAIN;
-
-out_unlock:
- spin_unlock(&hb->lock);
- return ret;
-
-pi_retry:
- cond_resched();
- goto retry;
-
-pi_faulted:
-
- ret = fault_in_user_writeable(uaddr);
- if (!ret)
- goto retry;
-
- return ret;
-}
-
-/**
- * handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
- * @hb: the hash_bucket futex_q was original enqueued on
- * @q: the futex_q woken while waiting to be requeued
- * @timeout: the timeout associated with the wait (NULL if none)
- *
- * Determine the cause for the early wakeup.
- *
- * Return:
- * -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR
- */
-static inline
-int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
- struct futex_q *q,
- struct hrtimer_sleeper *timeout)
-{
- int ret;
-
- /*
- * With the hb lock held, we avoid races while we process the wakeup.
- * We only need to hold hb (and not hb2) to ensure atomicity as the
- * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
- * It can't be requeued from uaddr2 to something else since we don't
- * support a PI aware source futex for requeue.
- */
- WARN_ON_ONCE(&hb->lock != q->lock_ptr);
-
- /*
- * We were woken prior to requeue by a timeout or a signal.
- * Unqueue the futex_q and determine which it was.
- */
- plist_del(&q->list, &hb->chain);
- hb_waiters_dec(hb);
-
- /* Handle spurious wakeups gracefully */
- ret = -EWOULDBLOCK;
- if (timeout && !timeout->task)
- ret = -ETIMEDOUT;
- else if (signal_pending(current))
- ret = -ERESTARTNOINTR;
- return ret;
-}
-
-/**
- * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
- * @uaddr: the futex we initially wait on (non-pi)
- * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
- * the same type, no requeueing from private to shared, etc.
- * @val: the expected value of uaddr
- * @abs_time: absolute timeout
- * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
- * @uaddr2: the pi futex we will take prior to returning to user-space
- *
- * The caller will wait on uaddr and will be requeued by futex_requeue() to
- * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
- * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
- * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
- * without one, the pi logic would not know which task to boost/deboost, if
- * there was a need to.
- *
- * We call schedule in futex_wait_queue_me() when we enqueue and return there
- * via the following--
- * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
- * 2) wakeup on uaddr2 after a requeue
- * 3) signal
- * 4) timeout
- *
- * If 3, cleanup and return -ERESTARTNOINTR.
- *
- * If 2, we may then block on trying to take the rt_mutex and return via:
- * 5) successful lock
- * 6) signal
- * 7) timeout
- * 8) other lock acquisition failure
- *
- * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
- *
- * If 4 or 7, we cleanup and return with -ETIMEDOUT.
- *
- * Return:
- * - 0 - On success;
- * - <0 - On error
- */
-static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
- u32 val, ktime_t *abs_time, u32 bitset,
- u32 __user *uaddr2)
-{
- struct hrtimer_sleeper timeout, *to;
- struct rt_mutex_waiter rt_waiter;
- struct futex_hash_bucket *hb;
- union futex_key key2 = FUTEX_KEY_INIT;
- struct futex_q q = futex_q_init;
- struct rt_mutex_base *pi_mutex;
- int res, ret;
-
- if (!IS_ENABLED(CONFIG_FUTEX_PI))
- return -ENOSYS;
-
- if (uaddr == uaddr2)
- return -EINVAL;
-
- if (!bitset)
- return -EINVAL;
-
- to = futex_setup_timer(abs_time, &timeout, flags,
- current->timer_slack_ns);
-
- /*
- * The waiter is allocated on our stack, manipulated by the requeue
- * code while we sleep on uaddr.
- */
- rt_mutex_init_waiter(&rt_waiter);
-
- ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
- if (unlikely(ret != 0))
- goto out;
-
- q.bitset = bitset;
- q.rt_waiter = &rt_waiter;
- q.requeue_pi_key = &key2;
-
- /*
- * Prepare to wait on uaddr. On success, it holds hb->lock and q
- * is initialized.
- */
- ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
- if (ret)
- goto out;
-
- /*
- * The check above which compares uaddrs is not sufficient for
- * shared futexes. We need to compare the keys:
- */
- if (match_futex(&q.key, &key2)) {
- queue_unlock(hb);
- ret = -EINVAL;
- goto out;
- }
-
- /* Queue the futex_q, drop the hb lock, wait for wakeup. */
- futex_wait_queue_me(hb, &q, to);
-
- switch (futex_requeue_pi_wakeup_sync(&q)) {
- case Q_REQUEUE_PI_IGNORE:
- /* The waiter is still on uaddr1 */
- spin_lock(&hb->lock);
- ret = handle_early_requeue_pi_wakeup(hb, &q, to);
- spin_unlock(&hb->lock);
- break;
-
- case Q_REQUEUE_PI_LOCKED:
- /* The requeue acquired the lock */
- if (q.pi_state && (q.pi_state->owner != current)) {
- spin_lock(q.lock_ptr);
- ret = fixup_owner(uaddr2, &q, true);
- /*
- * Drop the reference to the pi state which the
- * requeue_pi() code acquired for us.
- */
- put_pi_state(q.pi_state);
- spin_unlock(q.lock_ptr);
- /*
- * Adjust the return value. It's either -EFAULT or
- * success (1) but the caller expects 0 for success.
- */
- ret = ret < 0 ? ret : 0;
- }
- break;
-
- case Q_REQUEUE_PI_DONE:
- /* Requeue completed. Current is 'pi_blocked_on' the rtmutex */
- pi_mutex = &q.pi_state->pi_mutex;
- ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
-
- /* Current is not longer pi_blocked_on */
- spin_lock(q.lock_ptr);
- if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
- ret = 0;
-
- debug_rt_mutex_free_waiter(&rt_waiter);
- /*
- * Fixup the pi_state owner and possibly acquire the lock if we
- * haven't already.
- */
- res = fixup_owner(uaddr2, &q, !ret);
- /*
- * If fixup_owner() returned an error, propagate that. If it
- * acquired the lock, clear -ETIMEDOUT or -EINTR.
- */
- if (res)
- ret = (res < 0) ? res : 0;
-
- unqueue_me_pi(&q);
- spin_unlock(q.lock_ptr);
-
- if (ret == -EINTR) {
- /*
- * We've already been requeued, but cannot restart
- * by calling futex_lock_pi() directly. We could
- * restart this syscall, but it would detect that
- * the user space "val" changed and return
- * -EWOULDBLOCK. Save the overhead of the restart
- * and return -EWOULDBLOCK directly.
- */
- ret = -EWOULDBLOCK;
- }
- break;
- default:
- BUG();
- }
-
-out:
- if (to) {
- hrtimer_cancel(&to->timer);
- destroy_hrtimer_on_stack(&to->timer);
- }
- return ret;
-}
-
-/*
- * Support for robust futexes: the kernel cleans up held futexes at
- * thread exit time.
- *
- * Implementation: user-space maintains a per-thread list of locks it
- * is holding. Upon do_exit(), the kernel carefully walks this list,
- * and marks all locks that are owned by this thread with the
- * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
- * always manipulated with the lock held, so the list is private and
- * per-thread. Userspace also maintains a per-thread 'list_op_pending'
- * field, to allow the kernel to clean up if the thread dies after
- * acquiring the lock, but just before it could have added itself to
- * the list. There can only be one such pending lock.
- */
-
-/**
- * sys_set_robust_list() - Set the robust-futex list head of a task
- * @head: pointer to the list-head
- * @len: length of the list-head, as userspace expects
- */
-SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
- size_t, len)
-{
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
- /*
- * The kernel knows only one size for now:
- */
- if (unlikely(len != sizeof(*head)))
- return -EINVAL;
-
- current->robust_list = head;
-
- return 0;
-}
-
-/**
- * sys_get_robust_list() - Get the robust-futex list head of a task
- * @pid: pid of the process [zero for current task]
- * @head_ptr: pointer to a list-head pointer, the kernel fills it in
- * @len_ptr: pointer to a length field, the kernel fills in the header size
- */
-SYSCALL_DEFINE3(get_robust_list, int, pid,
- struct robust_list_head __user * __user *, head_ptr,
- size_t __user *, len_ptr)
-{
- struct robust_list_head __user *head;
- unsigned long ret;
- struct task_struct *p;
-
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
-
- rcu_read_lock();
-
- ret = -ESRCH;
- if (!pid)
- p = current;
- else {
- p = find_task_by_vpid(pid);
- if (!p)
- goto err_unlock;
- }
-
- ret = -EPERM;
- if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
- goto err_unlock;
-
- head = p->robust_list;
- rcu_read_unlock();
-
- if (put_user(sizeof(*head), len_ptr))
- return -EFAULT;
- return put_user(head, head_ptr);
-
-err_unlock:
- rcu_read_unlock();
-
- return ret;
-}
-
-/* Constants for the pending_op argument of handle_futex_death */
-#define HANDLE_DEATH_PENDING true
-#define HANDLE_DEATH_LIST false
-
-/*
- * Process a futex-list entry, check whether it's owned by the
- * dying task, and do notification if so:
- */
-static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
- bool pi, bool pending_op)
-{
- u32 uval, nval, mval;
- int err;
-
- /* Futex address must be 32bit aligned */
- if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
- return -1;
-
-retry:
- if (get_user(uval, uaddr))
- return -1;
-
- /*
- * Special case for regular (non PI) futexes. The unlock path in
- * user space has two race scenarios:
- *
- * 1. The unlock path releases the user space futex value and
- * before it can execute the futex() syscall to wake up
- * waiters it is killed.
- *
- * 2. A woken up waiter is killed before it can acquire the
- * futex in user space.
- *
- * In both cases the TID validation below prevents a wakeup of
- * potential waiters which can cause these waiters to block
- * forever.
- *
- * In both cases the following conditions are met:
- *
- * 1) task->robust_list->list_op_pending != NULL
- * @pending_op == true
- * 2) User space futex value == 0
- * 3) Regular futex: @pi == false
- *
- * If these conditions are met, it is safe to attempt waking up a
- * potential waiter without touching the user space futex value and
- * trying to set the OWNER_DIED bit. The user space futex value is
- * uncontended and the rest of the user space mutex state is
- * consistent, so a woken waiter will just take over the
- * uncontended futex. Setting the OWNER_DIED bit would create
- * inconsistent state and malfunction of the user space owner died
- * handling.
- */
- if (pending_op && !pi && !uval) {
- futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
- return 0;
- }
-
- if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
- return 0;
-
- /*
- * Ok, this dying thread is truly holding a futex
- * of interest. Set the OWNER_DIED bit atomically
- * via cmpxchg, and if the value had FUTEX_WAITERS
- * set, wake up a waiter (if any). (We have to do a
- * futex_wake() even if OWNER_DIED is already set -
- * to handle the rare but possible case of recursive
- * thread-death.) The rest of the cleanup is done in
- * userspace.
- */
- mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
-
- /*
- * We are not holding a lock here, but we want to have
- * the pagefault_disable/enable() protection because
- * we want to handle the fault gracefully. If the
- * access fails we try to fault in the futex with R/W
- * verification via get_user_pages. get_user() above
- * does not guarantee R/W access. If that fails we
- * give up and leave the futex locked.
- */
- if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
- switch (err) {
- case -EFAULT:
- if (fault_in_user_writeable(uaddr))
- return -1;
- goto retry;
-
- case -EAGAIN:
- cond_resched();
- goto retry;
-
- default:
- WARN_ON_ONCE(1);
- return err;
- }
- }
-
- if (nval != uval)
- goto retry;
-
- /*
- * Wake robust non-PI futexes here. The wakeup of
- * PI futexes happens in exit_pi_state():
- */
- if (!pi && (uval & FUTEX_WAITERS))
- futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
-
- return 0;
-}
-
-/*
- * Fetch a robust-list pointer. Bit 0 signals PI futexes:
- */
-static inline int fetch_robust_entry(struct robust_list __user **entry,
- struct robust_list __user * __user *head,
- unsigned int *pi)
-{
- unsigned long uentry;
-
- if (get_user(uentry, (unsigned long __user *)head))
- return -EFAULT;
-
- *entry = (void __user *)(uentry & ~1UL);
- *pi = uentry & 1;
-
- return 0;
-}
-
-/*
- * Walk curr->robust_list (very carefully, it's a userspace list!)
- * and mark any locks found there dead, and notify any waiters.
- *
- * We silently return on any sign of list-walking problem.
- */
-static void exit_robust_list(struct task_struct *curr)
-{
- struct robust_list_head __user *head = curr->robust_list;
- struct robust_list __user *entry, *next_entry, *pending;
- unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
- unsigned int next_pi;
- unsigned long futex_offset;
- int rc;
-
- if (!futex_cmpxchg_enabled)
- return;
-
- /*
- * Fetch the list head (which was registered earlier, via
- * sys_set_robust_list()):
- */
- if (fetch_robust_entry(&entry, &head->list.next, &pi))
- return;
- /*
- * Fetch the relative futex offset:
- */
- if (get_user(futex_offset, &head->futex_offset))
- return;
- /*
- * Fetch any possibly pending lock-add first, and handle it
- * if it exists:
- */
- if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
- return;
-
- next_entry = NULL; /* avoid warning with gcc */
- while (entry != &head->list) {
- /*
- * Fetch the next entry in the list before calling
- * handle_futex_death:
- */
- rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
- /*
- * A pending lock might already be on the list, so
- * don't process it twice:
- */
- if (entry != pending) {
- if (handle_futex_death((void __user *)entry + futex_offset,
- curr, pi, HANDLE_DEATH_LIST))
- return;
- }
- if (rc)
- return;
- entry = next_entry;
- pi = next_pi;
- /*
- * Avoid excessively long or circular lists:
- */
- if (!--limit)
- break;
-
- cond_resched();
- }
-
- if (pending) {
- handle_futex_death((void __user *)pending + futex_offset,
- curr, pip, HANDLE_DEATH_PENDING);
- }
-}
-
-static void futex_cleanup(struct task_struct *tsk)
-{
- if (unlikely(tsk->robust_list)) {
- exit_robust_list(tsk);
- tsk->robust_list = NULL;
- }
-
-#ifdef CONFIG_COMPAT
- if (unlikely(tsk->compat_robust_list)) {
- compat_exit_robust_list(tsk);
- tsk->compat_robust_list = NULL;
- }
-#endif
-
- if (unlikely(!list_empty(&tsk->pi_state_list)))
- exit_pi_state_list(tsk);
-}
-
-/**
- * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
- * @tsk: task to set the state on
- *
- * Set the futex exit state of the task lockless. The futex waiter code
- * observes that state when a task is exiting and loops until the task has
- * actually finished the futex cleanup. The worst case for this is that the
- * waiter runs through the wait loop until the state becomes visible.
- *
- * This is called from the recursive fault handling path in do_exit().
- *
- * This is best effort. Either the futex exit code has run already or
- * not. If the OWNER_DIED bit has been set on the futex then the waiter can
- * take it over. If not, the problem is pushed back to user space. If the
- * futex exit code did not run yet, then an already queued waiter might
- * block forever, but there is nothing which can be done about that.
- */
-void futex_exit_recursive(struct task_struct *tsk)
-{
- /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
- if (tsk->futex_state == FUTEX_STATE_EXITING)
- mutex_unlock(&tsk->futex_exit_mutex);
- tsk->futex_state = FUTEX_STATE_DEAD;
-}
-
-static void futex_cleanup_begin(struct task_struct *tsk)
-{
- /*
- * Prevent various race issues against a concurrent incoming waiter
- * including live locks by forcing the waiter to block on
- * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
- * attach_to_pi_owner().
- */
- mutex_lock(&tsk->futex_exit_mutex);
-
- /*
- * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
- *
- * This ensures that all subsequent checks of tsk->futex_state in
- * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
- * tsk->pi_lock held.
- *
- * It guarantees also that a pi_state which was queued right before
- * the state change under tsk->pi_lock by a concurrent waiter must
- * be observed in exit_pi_state_list().
- */
- raw_spin_lock_irq(&tsk->pi_lock);
- tsk->futex_state = FUTEX_STATE_EXITING;
- raw_spin_unlock_irq(&tsk->pi_lock);
-}
-
-static void futex_cleanup_end(struct task_struct *tsk, int state)
-{
- /*
- * Lockless store. The only side effect is that an observer might
- * take another loop until it becomes visible.
- */
- tsk->futex_state = state;
- /*
- * Drop the exit protection. This unblocks waiters which observed
- * FUTEX_STATE_EXITING to reevaluate the state.
- */
- mutex_unlock(&tsk->futex_exit_mutex);
-}
-
-void futex_exec_release(struct task_struct *tsk)
-{
- /*
- * The state handling is done for consistency, but in the case of
- * exec() there is no way to prevent further damage as the PID stays
- * the same. But for the unlikely and arguably buggy case that a
- * futex is held on exec(), this provides at least as much state
- * consistency protection which is possible.
- */
- futex_cleanup_begin(tsk);
- futex_cleanup(tsk);
- /*
- * Reset the state to FUTEX_STATE_OK. The task is alive and about
- * exec a new binary.
- */
- futex_cleanup_end(tsk, FUTEX_STATE_OK);
-}
-
-void futex_exit_release(struct task_struct *tsk)
-{
- futex_cleanup_begin(tsk);
- futex_cleanup(tsk);
- futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
-}
-
-long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
- u32 __user *uaddr2, u32 val2, u32 val3)
-{
- int cmd = op & FUTEX_CMD_MASK;
- unsigned int flags = 0;
-
- if (!(op & FUTEX_PRIVATE_FLAG))
- flags |= FLAGS_SHARED;
-
- if (op & FUTEX_CLOCK_REALTIME) {
- flags |= FLAGS_CLOCKRT;
- if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
- cmd != FUTEX_LOCK_PI2)
- return -ENOSYS;
- }
-
- switch (cmd) {
- case FUTEX_LOCK_PI:
- case FUTEX_LOCK_PI2:
- case FUTEX_UNLOCK_PI:
- case FUTEX_TRYLOCK_PI:
- case FUTEX_WAIT_REQUEUE_PI:
- case FUTEX_CMP_REQUEUE_PI:
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
- }
-
- switch (cmd) {
- case FUTEX_WAIT:
- val3 = FUTEX_BITSET_MATCH_ANY;
- fallthrough;
- case FUTEX_WAIT_BITSET:
- return futex_wait(uaddr, flags, val, timeout, val3);
- case FUTEX_WAKE:
- val3 = FUTEX_BITSET_MATCH_ANY;
- fallthrough;
- case FUTEX_WAKE_BITSET:
- return futex_wake(uaddr, flags, val, val3);
- case FUTEX_REQUEUE:
- return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
- case FUTEX_CMP_REQUEUE:
- return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
- case FUTEX_WAKE_OP:
- return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
- case FUTEX_LOCK_PI:
- flags |= FLAGS_CLOCKRT;
- fallthrough;
- case FUTEX_LOCK_PI2:
- return futex_lock_pi(uaddr, flags, timeout, 0);
- case FUTEX_UNLOCK_PI:
- return futex_unlock_pi(uaddr, flags);
- case FUTEX_TRYLOCK_PI:
- return futex_lock_pi(uaddr, flags, NULL, 1);
- case FUTEX_WAIT_REQUEUE_PI:
- val3 = FUTEX_BITSET_MATCH_ANY;
- return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
- uaddr2);
- case FUTEX_CMP_REQUEUE_PI:
- return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
- }
- return -ENOSYS;
-}
-
-static __always_inline bool futex_cmd_has_timeout(u32 cmd)
-{
- switch (cmd) {
- case FUTEX_WAIT:
- case FUTEX_LOCK_PI:
- case FUTEX_LOCK_PI2:
- case FUTEX_WAIT_BITSET:
- case FUTEX_WAIT_REQUEUE_PI:
- return true;
- }
- return false;
-}
-
-static __always_inline int
-futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
-{
- if (!timespec64_valid(ts))
- return -EINVAL;
-
- *t = timespec64_to_ktime(*ts);
- if (cmd == FUTEX_WAIT)
- *t = ktime_add_safe(ktime_get(), *t);
- else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
- *t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
- return 0;
-}
-
-SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
- const struct __kernel_timespec __user *, utime,
- u32 __user *, uaddr2, u32, val3)
-{
- int ret, cmd = op & FUTEX_CMD_MASK;
- ktime_t t, *tp = NULL;
- struct timespec64 ts;
-
- if (utime && futex_cmd_has_timeout(cmd)) {
- if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
- return -EFAULT;
- if (get_timespec64(&ts, utime))
- return -EFAULT;
- ret = futex_init_timeout(cmd, op, &ts, &t);
- if (ret)
- return ret;
- tp = &t;
- }
-
- return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
-}
-
-#ifdef CONFIG_COMPAT
-/*
- * Fetch a robust-list pointer. Bit 0 signals PI futexes:
- */
-static inline int
-compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
- compat_uptr_t __user *head, unsigned int *pi)
-{
- if (get_user(*uentry, head))
- return -EFAULT;
-
- *entry = compat_ptr((*uentry) & ~1);
- *pi = (unsigned int)(*uentry) & 1;
-
- return 0;
-}
-
-static void __user *futex_uaddr(struct robust_list __user *entry,
- compat_long_t futex_offset)
-{
- compat_uptr_t base = ptr_to_compat(entry);
- void __user *uaddr = compat_ptr(base + futex_offset);
-
- return uaddr;
-}
-
-/*
- * Walk curr->robust_list (very carefully, it's a userspace list!)
- * and mark any locks found there dead, and notify any waiters.
- *
- * We silently return on any sign of list-walking problem.
- */
-static void compat_exit_robust_list(struct task_struct *curr)
-{
- struct compat_robust_list_head __user *head = curr->compat_robust_list;
- struct robust_list __user *entry, *next_entry, *pending;
- unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
- unsigned int next_pi;
- compat_uptr_t uentry, next_uentry, upending;
- compat_long_t futex_offset;
- int rc;
-
- if (!futex_cmpxchg_enabled)
- return;
-
- /*
- * Fetch the list head (which was registered earlier, via
- * sys_set_robust_list()):
- */
- if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
- return;
- /*
- * Fetch the relative futex offset:
- */
- if (get_user(futex_offset, &head->futex_offset))
- return;
- /*
- * Fetch any possibly pending lock-add first, and handle it
- * if it exists:
- */
- if (compat_fetch_robust_entry(&upending, &pending,
- &head->list_op_pending, &pip))
- return;
-
- next_entry = NULL; /* avoid warning with gcc */
- while (entry != (struct robust_list __user *) &head->list) {
- /*
- * Fetch the next entry in the list before calling
- * handle_futex_death:
- */
- rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
- (compat_uptr_t __user *)&entry->next, &next_pi);
- /*
- * A pending lock might already be on the list, so
- * dont process it twice:
- */
- if (entry != pending) {
- void __user *uaddr = futex_uaddr(entry, futex_offset);
-
- if (handle_futex_death(uaddr, curr, pi,
- HANDLE_DEATH_LIST))
- return;
- }
- if (rc)
- return;
- uentry = next_uentry;
- entry = next_entry;
- pi = next_pi;
- /*
- * Avoid excessively long or circular lists:
- */
- if (!--limit)
- break;
-
- cond_resched();
- }
- if (pending) {
- void __user *uaddr = futex_uaddr(pending, futex_offset);
-
- handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
- }
-}
-
-COMPAT_SYSCALL_DEFINE2(set_robust_list,
- struct compat_robust_list_head __user *, head,
- compat_size_t, len)
-{
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
-
- if (unlikely(len != sizeof(*head)))
- return -EINVAL;
-
- current->compat_robust_list = head;
-
- return 0;
-}
-
-COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
- compat_uptr_t __user *, head_ptr,
- compat_size_t __user *, len_ptr)
-{
- struct compat_robust_list_head __user *head;
- unsigned long ret;
- struct task_struct *p;
-
- if (!futex_cmpxchg_enabled)
- return -ENOSYS;
-
- rcu_read_lock();
-
- ret = -ESRCH;
- if (!pid)
- p = current;
- else {
- p = find_task_by_vpid(pid);
- if (!p)
- goto err_unlock;
- }
-
- ret = -EPERM;
- if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
- goto err_unlock;
-
- head = p->compat_robust_list;
- rcu_read_unlock();
-
- if (put_user(sizeof(*head), len_ptr))
- return -EFAULT;
- return put_user(ptr_to_compat(head), head_ptr);
-
-err_unlock:
- rcu_read_unlock();
-
- return ret;
-}
-#endif /* CONFIG_COMPAT */
-
-#ifdef CONFIG_COMPAT_32BIT_TIME
-SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
- const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
- u32, val3)
-{
- int ret, cmd = op & FUTEX_CMD_MASK;
- ktime_t t, *tp = NULL;
- struct timespec64 ts;
-
- if (utime && futex_cmd_has_timeout(cmd)) {
- if (get_old_timespec32(&ts, utime))
- return -EFAULT;
- ret = futex_init_timeout(cmd, op, &ts, &t);
- if (ret)
- return ret;
- tp = &t;
- }
-
- return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
-}
-#endif /* CONFIG_COMPAT_32BIT_TIME */
-
-static void __init futex_detect_cmpxchg(void)
-{
-#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
- u32 curval;
-
- /*
- * This will fail and we want it. Some arch implementations do
- * runtime detection of the futex_atomic_cmpxchg_inatomic()
- * functionality. We want to know that before we call in any
- * of the complex code paths. Also we want to prevent
- * registration of robust lists in that case. NULL is
- * guaranteed to fault and we get -EFAULT on functional
- * implementation, the non-functional ones will return
- * -ENOSYS.
- */
- if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
- futex_cmpxchg_enabled = 1;
-#endif
-}
-
-static int __init futex_init(void)
-{
- unsigned int futex_shift;
- unsigned long i;
-
-#if CONFIG_BASE_SMALL
- futex_hashsize = 16;
-#else
- futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
-#endif
-
- futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
- futex_hashsize, 0,
- futex_hashsize < 256 ? HASH_SMALL : 0,
- &futex_shift, NULL,
- futex_hashsize, futex_hashsize);
- futex_hashsize = 1UL << futex_shift;
-
- futex_detect_cmpxchg();
-
- for (i = 0; i < futex_hashsize; i++) {
- atomic_set(&futex_queues[i].waiters, 0);
- plist_head_init(&futex_queues[i].chain);
- spin_lock_init(&futex_queues[i].lock);
- }
-
- return 0;
-}
-core_initcall(futex_init);
--- /dev/null
+++ b/kernel/futex/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-y += core.o
--- /dev/null
+++ b/kernel/futex/core.c
@@ -0,0 +1,4272 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Fast Userspace Mutexes (which I call "Futexes!").
+ * (C) Rusty Russell, IBM 2002
+ *
+ * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
+ * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
+ *
+ * Removed page pinning, fix privately mapped COW pages and other cleanups
+ * (C) Copyright 2003, 2004 Jamie Lokier
+ *
+ * Robust futex support started by Ingo Molnar
+ * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
+ * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
+ *
+ * PI-futex support started by Ingo Molnar and Thomas Gleixner
+ * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@...hat.com>
+ * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@...esys.com>
+ *
+ * PRIVATE futexes by Eric Dumazet
+ * Copyright (C) 2007 Eric Dumazet <dada1@...mosbay.com>
+ *
+ * Requeue-PI support by Darren Hart <dvhltc@...ibm.com>
+ * Copyright (C) IBM Corporation, 2009
+ * Thanks to Thomas Gleixner for conceptual design and careful reviews.
+ *
+ * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
+ * enough at me, Linus for the original (flawed) idea, Matthew
+ * Kirkwood for proof-of-concept implementation.
+ *
+ * "The futexes are also cursed."
+ * "But they come in a choice of three flavours!"
+ */
+#include <linux/compat.h>
+#include <linux/jhash.h>
+#include <linux/pagemap.h>
+#include <linux/syscalls.h>
+#include <linux/freezer.h>
+#include <linux/memblock.h>
+#include <linux/fault-inject.h>
+#include <linux/time_namespace.h>
+
+#include <asm/futex.h>
+
+#include "../locking/rtmutex_common.h"
+
+/*
+ * READ this before attempting to hack on futexes!
+ *
+ * Basic futex operation and ordering guarantees
+ * =============================================
+ *
+ * The waiter reads the futex value in user space and calls
+ * futex_wait(). This function computes the hash bucket and acquires
+ * the hash bucket lock. After that it reads the futex user space value
+ * again and verifies that the data has not changed. If it has not changed
+ * it enqueues itself into the hash bucket, releases the hash bucket lock
+ * and schedules.
+ *
+ * The waker side modifies the user space value of the futex and calls
+ * futex_wake(). This function computes the hash bucket and acquires the
+ * hash bucket lock. Then it looks for waiters on that futex in the hash
+ * bucket and wakes them.
+ *
+ * In futex wake up scenarios where no tasks are blocked on a futex, taking
+ * the hb spinlock can be avoided and simply return. In order for this
+ * optimization to work, ordering guarantees must exist so that the waiter
+ * being added to the list is acknowledged when the list is concurrently being
+ * checked by the waker, avoiding scenarios like the following:
+ *
+ * CPU 0 CPU 1
+ * val = *futex;
+ * sys_futex(WAIT, futex, val);
+ * futex_wait(futex, val);
+ * uval = *futex;
+ * *futex = newval;
+ * sys_futex(WAKE, futex);
+ * futex_wake(futex);
+ * if (queue_empty())
+ * return;
+ * if (uval == val)
+ * lock(hash_bucket(futex));
+ * queue();
+ * unlock(hash_bucket(futex));
+ * schedule();
+ *
+ * This would cause the waiter on CPU 0 to wait forever because it
+ * missed the transition of the user space value from val to newval
+ * and the waker did not find the waiter in the hash bucket queue.
+ *
+ * The correct serialization ensures that a waiter either observes
+ * the changed user space value before blocking or is woken by a
+ * concurrent waker:
+ *
+ * CPU 0 CPU 1
+ * val = *futex;
+ * sys_futex(WAIT, futex, val);
+ * futex_wait(futex, val);
+ *
+ * waiters++; (a)
+ * smp_mb(); (A) <-- paired with -.
+ * |
+ * lock(hash_bucket(futex)); |
+ * |
+ * uval = *futex; |
+ * | *futex = newval;
+ * | sys_futex(WAKE, futex);
+ * | futex_wake(futex);
+ * |
+ * `--------> smp_mb(); (B)
+ * if (uval == val)
+ * queue();
+ * unlock(hash_bucket(futex));
+ * schedule(); if (waiters)
+ * lock(hash_bucket(futex));
+ * else wake_waiters(futex);
+ * waiters--; (b) unlock(hash_bucket(futex));
+ *
+ * Where (A) orders the waiters increment and the futex value read through
+ * atomic operations (see hb_waiters_inc) and where (B) orders the write
+ * to futex and the waiters read (see hb_waiters_pending()).
+ *
+ * This yields the following case (where X:=waiters, Y:=futex):
+ *
+ * X = Y = 0
+ *
+ * w[X]=1 w[Y]=1
+ * MB MB
+ * r[Y]=y r[X]=x
+ *
+ * Which guarantees that x==0 && y==0 is impossible; which translates back into
+ * the guarantee that we cannot both miss the futex variable change and the
+ * enqueue.
+ *
+ * Note that a new waiter is accounted for in (a) even when it is possible that
+ * the wait call can return error, in which case we backtrack from it in (b).
+ * Refer to the comment in queue_lock().
+ *
+ * Similarly, in order to account for waiters being requeued on another
+ * address we always increment the waiters for the destination bucket before
+ * acquiring the lock. It then decrements them again after releasing it -
+ * the code that actually moves the futex(es) between hash buckets (requeue_futex)
+ * will do the additional required waiter count housekeeping. This is done for
+ * double_lock_hb() and double_unlock_hb(), respectively.
+ */
+
+#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
+#define futex_cmpxchg_enabled 1
+#else
+static int __read_mostly futex_cmpxchg_enabled;
+#endif
+
+/*
+ * Futex flags used to encode options to functions and preserve them across
+ * restarts.
+ */
+#ifdef CONFIG_MMU
+# define FLAGS_SHARED 0x01
+#else
+/*
+ * NOMMU does not have per process address space. Let the compiler optimize
+ * code away.
+ */
+# define FLAGS_SHARED 0x00
+#endif
+#define FLAGS_CLOCKRT 0x02
+#define FLAGS_HAS_TIMEOUT 0x04
+
+/*
+ * Priority Inheritance state:
+ */
+struct futex_pi_state {
+ /*
+ * list of 'owned' pi_state instances - these have to be
+ * cleaned up in do_exit() if the task exits prematurely:
+ */
+ struct list_head list;
+
+ /*
+ * The PI object:
+ */
+ struct rt_mutex_base pi_mutex;
+
+ struct task_struct *owner;
+ refcount_t refcount;
+
+ union futex_key key;
+} __randomize_layout;
+
+/**
+ * struct futex_q - The hashed futex queue entry, one per waiting task
+ * @list: priority-sorted list of tasks waiting on this futex
+ * @task: the task waiting on the futex
+ * @lock_ptr: the hash bucket lock
+ * @key: the key the futex is hashed on
+ * @pi_state: optional priority inheritance state
+ * @rt_waiter: rt_waiter storage for use with requeue_pi
+ * @requeue_pi_key: the requeue_pi target futex key
+ * @bitset: bitset for the optional bitmasked wakeup
+ * @requeue_state: State field for futex_requeue_pi()
+ * @requeue_wait: RCU wait for futex_requeue_pi() (RT only)
+ *
+ * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
+ * we can wake only the relevant ones (hashed queues may be shared).
+ *
+ * A futex_q has a woken state, just like tasks have TASK_RUNNING.
+ * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
+ * The order of wakeup is always to make the first condition true, then
+ * the second.
+ *
+ * PI futexes are typically woken before they are removed from the hash list via
+ * the rt_mutex code. See unqueue_me_pi().
+ */
+struct futex_q {
+ struct plist_node list;
+
+ struct task_struct *task;
+ spinlock_t *lock_ptr;
+ union futex_key key;
+ struct futex_pi_state *pi_state;
+ struct rt_mutex_waiter *rt_waiter;
+ union futex_key *requeue_pi_key;
+ u32 bitset;
+ atomic_t requeue_state;
+#ifdef CONFIG_PREEMPT_RT
+ struct rcuwait requeue_wait;
+#endif
+} __randomize_layout;
+
+/*
+ * On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
+ * underlying rtmutex. The task which is about to be requeued could have
+ * just woken up (timeout, signal). After the wake up the task has to
+ * acquire hash bucket lock, which is held by the requeue code. As a task
+ * can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking
+ * and the hash bucket lock blocking would collide and corrupt state.
+ *
+ * On !PREEMPT_RT this is not a problem and everything could be serialized
+ * on hash bucket lock, but aside of having the benefit of common code,
+ * this allows to avoid doing the requeue when the task is already on the
+ * way out and taking the hash bucket lock of the original uaddr1 when the
+ * requeue has been completed.
+ *
+ * The following state transitions are valid:
+ *
+ * On the waiter side:
+ * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IGNORE
+ * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT
+ *
+ * On the requeue side:
+ * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_INPROGRESS
+ * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_DONE/LOCKED
+ * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_NONE (requeue failed)
+ * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_DONE/LOCKED
+ * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_IGNORE (requeue failed)
+ *
+ * The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this
+ * signals that the waiter is already on the way out. It also means that
+ * the waiter is still on the 'wait' futex, i.e. uaddr1.
+ *
+ * The waiter side signals early wakeup to the requeue side either through
+ * setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending
+ * on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately
+ * proceed to take the hash bucket lock of uaddr1. If it set state to WAIT,
+ * which means the wakeup is interleaving with a requeue in progress it has
+ * to wait for the requeue side to change the state. Either to DONE/LOCKED
+ * or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex
+ * and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by
+ * the requeue side when the requeue attempt failed via deadlock detection
+ * and therefore the waiter q is still on the uaddr1 futex.
+ */
+enum {
+ Q_REQUEUE_PI_NONE = 0,
+ Q_REQUEUE_PI_IGNORE,
+ Q_REQUEUE_PI_IN_PROGRESS,
+ Q_REQUEUE_PI_WAIT,
+ Q_REQUEUE_PI_DONE,
+ Q_REQUEUE_PI_LOCKED,
+};
+
+static const struct futex_q futex_q_init = {
+ /* list gets initialized in queue_me()*/
+ .key = FUTEX_KEY_INIT,
+ .bitset = FUTEX_BITSET_MATCH_ANY,
+ .requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE),
+};
+
+/*
+ * Hash buckets are shared by all the futex_keys that hash to the same
+ * location. Each key may have multiple futex_q structures, one for each task
+ * waiting on a futex.
+ */
+struct futex_hash_bucket {
+ atomic_t waiters;
+ spinlock_t lock;
+ struct plist_head chain;
+} ____cacheline_aligned_in_smp;
+
+/*
+ * The base of the bucket array and its size are always used together
+ * (after initialization only in hash_futex()), so ensure that they
+ * reside in the same cacheline.
+ */
+static struct {
+ struct futex_hash_bucket *queues;
+ unsigned long hashsize;
+} __futex_data __read_mostly __aligned(2*sizeof(long));
+#define futex_queues (__futex_data.queues)
+#define futex_hashsize (__futex_data.hashsize)
+
+
+/*
+ * Fault injections for futexes.
+ */
+#ifdef CONFIG_FAIL_FUTEX
+
+static struct {
+ struct fault_attr attr;
+
+ bool ignore_private;
+} fail_futex = {
+ .attr = FAULT_ATTR_INITIALIZER,
+ .ignore_private = false,
+};
+
+static int __init setup_fail_futex(char *str)
+{
+ return setup_fault_attr(&fail_futex.attr, str);
+}
+__setup("fail_futex=", setup_fail_futex);
+
+static bool should_fail_futex(bool fshared)
+{
+ if (fail_futex.ignore_private && !fshared)
+ return false;
+
+ return should_fail(&fail_futex.attr, 1);
+}
+
+#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
+
+static int __init fail_futex_debugfs(void)
+{
+ umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
+ struct dentry *dir;
+
+ dir = fault_create_debugfs_attr("fail_futex", NULL,
+ &fail_futex.attr);
+ if (IS_ERR(dir))
+ return PTR_ERR(dir);
+
+ debugfs_create_bool("ignore-private", mode, dir,
+ &fail_futex.ignore_private);
+ return 0;
+}
+
+late_initcall(fail_futex_debugfs);
+
+#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
+
+#else
+static inline bool should_fail_futex(bool fshared)
+{
+ return false;
+}
+#endif /* CONFIG_FAIL_FUTEX */
+
+#ifdef CONFIG_COMPAT
+static void compat_exit_robust_list(struct task_struct *curr);
+#endif
+
+/*
+ * Reflects a new waiter being added to the waitqueue.
+ */
+static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
+{
+#ifdef CONFIG_SMP
+ atomic_inc(&hb->waiters);
+ /*
+ * Full barrier (A), see the ordering comment above.
+ */
+ smp_mb__after_atomic();
+#endif
+}
+
+/*
+ * Reflects a waiter being removed from the waitqueue by wakeup
+ * paths.
+ */
+static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
+{
+#ifdef CONFIG_SMP
+ atomic_dec(&hb->waiters);
+#endif
+}
+
+static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
+{
+#ifdef CONFIG_SMP
+ /*
+ * Full barrier (B), see the ordering comment above.
+ */
+ smp_mb();
+ return atomic_read(&hb->waiters);
+#else
+ return 1;
+#endif
+}
+
+/**
+ * hash_futex - Return the hash bucket in the global hash
+ * @key: Pointer to the futex key for which the hash is calculated
+ *
+ * We hash on the keys returned from get_futex_key (see below) and return the
+ * corresponding hash bucket in the global hash.
+ */
+static struct futex_hash_bucket *hash_futex(union futex_key *key)
+{
+ u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
+ key->both.offset);
+
+ return &futex_queues[hash & (futex_hashsize - 1)];
+}
+
+
+/**
+ * match_futex - Check whether two futex keys are equal
+ * @key1: Pointer to key1
+ * @key2: Pointer to key2
+ *
+ * Return 1 if two futex_keys are equal, 0 otherwise.
+ */
+static inline int match_futex(union futex_key *key1, union futex_key *key2)
+{
+ return (key1 && key2
+ && key1->both.word == key2->both.word
+ && key1->both.ptr == key2->both.ptr
+ && key1->both.offset == key2->both.offset);
+}
+
+enum futex_access {
+ FUTEX_READ,
+ FUTEX_WRITE
+};
+
+/**
+ * futex_setup_timer - set up the sleeping hrtimer.
+ * @time: ptr to the given timeout value
+ * @timeout: the hrtimer_sleeper structure to be set up
+ * @flags: futex flags
+ * @range_ns: optional range in ns
+ *
+ * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
+ * value given
+ */
+static inline struct hrtimer_sleeper *
+futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
+ int flags, u64 range_ns)
+{
+ if (!time)
+ return NULL;
+
+ hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
+ CLOCK_REALTIME : CLOCK_MONOTONIC,
+ HRTIMER_MODE_ABS);
+ /*
+ * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
+ * effectively the same as calling hrtimer_set_expires().
+ */
+ hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
+
+ return timeout;
+}
+
+/*
+ * Generate a machine wide unique identifier for this inode.
+ *
+ * This relies on u64 not wrapping in the life-time of the machine; which with
+ * 1ns resolution means almost 585 years.
+ *
+ * This further relies on the fact that a well formed program will not unmap
+ * the file while it has a (shared) futex waiting on it. This mapping will have
+ * a file reference which pins the mount and inode.
+ *
+ * If for some reason an inode gets evicted and read back in again, it will get
+ * a new sequence number and will _NOT_ match, even though it is the exact same
+ * file.
+ *
+ * It is important that match_futex() will never have a false-positive, esp.
+ * for PI futexes that can mess up the state. The above argues that false-negatives
+ * are only possible for malformed programs.
+ */
+static u64 get_inode_sequence_number(struct inode *inode)
+{
+ static atomic64_t i_seq;
+ u64 old;
+
+ /* Does the inode already have a sequence number? */
+ old = atomic64_read(&inode->i_sequence);
+ if (likely(old))
+ return old;
+
+ for (;;) {
+ u64 new = atomic64_add_return(1, &i_seq);
+ if (WARN_ON_ONCE(!new))
+ continue;
+
+ old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
+ if (old)
+ return old;
+ return new;
+ }
+}
+
+/**
+ * get_futex_key() - Get parameters which are the keys for a futex
+ * @uaddr: virtual address of the futex
+ * @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
+ * @key: address where result is stored.
+ * @rw: mapping needs to be read/write (values: FUTEX_READ,
+ * FUTEX_WRITE)
+ *
+ * Return: a negative error code or 0
+ *
+ * The key words are stored in @key on success.
+ *
+ * For shared mappings (when @fshared), the key is:
+ *
+ * ( inode->i_sequence, page->index, offset_within_page )
+ *
+ * [ also see get_inode_sequence_number() ]
+ *
+ * For private mappings (or when !@...ared), the key is:
+ *
+ * ( current->mm, address, 0 )
+ *
+ * This allows (cross process, where applicable) identification of the futex
+ * without keeping the page pinned for the duration of the FUTEX_WAIT.
+ *
+ * lock_page() might sleep, the caller should not hold a spinlock.
+ */
+static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
+ enum futex_access rw)
+{
+ unsigned long address = (unsigned long)uaddr;
+ struct mm_struct *mm = current->mm;
+ struct page *page, *tail;
+ struct address_space *mapping;
+ int err, ro = 0;
+
+ /*
+ * The futex address must be "naturally" aligned.
+ */
+ key->both.offset = address % PAGE_SIZE;
+ if (unlikely((address % sizeof(u32)) != 0))
+ return -EINVAL;
+ address -= key->both.offset;
+
+ if (unlikely(!access_ok(uaddr, sizeof(u32))))
+ return -EFAULT;
+
+ if (unlikely(should_fail_futex(fshared)))
+ return -EFAULT;
+
+ /*
+ * PROCESS_PRIVATE futexes are fast.
+ * As the mm cannot disappear under us and the 'key' only needs
+ * virtual address, we dont even have to find the underlying vma.
+ * Note : We do have to check 'uaddr' is a valid user address,
+ * but access_ok() should be faster than find_vma()
+ */
+ if (!fshared) {
+ key->private.mm = mm;
+ key->private.address = address;
+ return 0;
+ }
+
+again:
+ /* Ignore any VERIFY_READ mapping (futex common case) */
+ if (unlikely(should_fail_futex(true)))
+ return -EFAULT;
+
+ err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
+ /*
+ * If write access is not required (eg. FUTEX_WAIT), try
+ * and get read-only access.
+ */
+ if (err == -EFAULT && rw == FUTEX_READ) {
+ err = get_user_pages_fast(address, 1, 0, &page);
+ ro = 1;
+ }
+ if (err < 0)
+ return err;
+ else
+ err = 0;
+
+ /*
+ * The treatment of mapping from this point on is critical. The page
+ * lock protects many things but in this context the page lock
+ * stabilizes mapping, prevents inode freeing in the shared
+ * file-backed region case and guards against movement to swap cache.
+ *
+ * Strictly speaking the page lock is not needed in all cases being
+ * considered here and page lock forces unnecessarily serialization
+ * From this point on, mapping will be re-verified if necessary and
+ * page lock will be acquired only if it is unavoidable
+ *
+ * Mapping checks require the head page for any compound page so the
+ * head page and mapping is looked up now. For anonymous pages, it
+ * does not matter if the page splits in the future as the key is
+ * based on the address. For filesystem-backed pages, the tail is
+ * required as the index of the page determines the key. For
+ * base pages, there is no tail page and tail == page.
+ */
+ tail = page;
+ page = compound_head(page);
+ mapping = READ_ONCE(page->mapping);
+
+ /*
+ * If page->mapping is NULL, then it cannot be a PageAnon
+ * page; but it might be the ZERO_PAGE or in the gate area or
+ * in a special mapping (all cases which we are happy to fail);
+ * or it may have been a good file page when get_user_pages_fast
+ * found it, but truncated or holepunched or subjected to
+ * invalidate_complete_page2 before we got the page lock (also
+ * cases which we are happy to fail). And we hold a reference,
+ * so refcount care in invalidate_complete_page's remove_mapping
+ * prevents drop_caches from setting mapping to NULL beneath us.
+ *
+ * The case we do have to guard against is when memory pressure made
+ * shmem_writepage move it from filecache to swapcache beneath us:
+ * an unlikely race, but we do need to retry for page->mapping.
+ */
+ if (unlikely(!mapping)) {
+ int shmem_swizzled;
+
+ /*
+ * Page lock is required to identify which special case above
+ * applies. If this is really a shmem page then the page lock
+ * will prevent unexpected transitions.
+ */
+ lock_page(page);
+ shmem_swizzled = PageSwapCache(page) || page->mapping;
+ unlock_page(page);
+ put_page(page);
+
+ if (shmem_swizzled)
+ goto again;
+
+ return -EFAULT;
+ }
+
+ /*
+ * Private mappings are handled in a simple way.
+ *
+ * If the futex key is stored on an anonymous page, then the associated
+ * object is the mm which is implicitly pinned by the calling process.
+ *
+ * NOTE: When userspace waits on a MAP_SHARED mapping, even if
+ * it's a read-only handle, it's expected that futexes attach to
+ * the object not the particular process.
+ */
+ if (PageAnon(page)) {
+ /*
+ * A RO anonymous page will never change and thus doesn't make
+ * sense for futex operations.
+ */
+ if (unlikely(should_fail_futex(true)) || ro) {
+ err = -EFAULT;
+ goto out;
+ }
+
+ key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
+ key->private.mm = mm;
+ key->private.address = address;
+
+ } else {
+ struct inode *inode;
+
+ /*
+ * The associated futex object in this case is the inode and
+ * the page->mapping must be traversed. Ordinarily this should
+ * be stabilised under page lock but it's not strictly
+ * necessary in this case as we just want to pin the inode, not
+ * update the radix tree or anything like that.
+ *
+ * The RCU read lock is taken as the inode is finally freed
+ * under RCU. If the mapping still matches expectations then the
+ * mapping->host can be safely accessed as being a valid inode.
+ */
+ rcu_read_lock();
+
+ if (READ_ONCE(page->mapping) != mapping) {
+ rcu_read_unlock();
+ put_page(page);
+
+ goto again;
+ }
+
+ inode = READ_ONCE(mapping->host);
+ if (!inode) {
+ rcu_read_unlock();
+ put_page(page);
+
+ goto again;
+ }
+
+ key->both.offset |= FUT_OFF_INODE; /* inode-based key */
+ key->shared.i_seq = get_inode_sequence_number(inode);
+ key->shared.pgoff = page_to_pgoff(tail);
+ rcu_read_unlock();
+ }
+
+out:
+ put_page(page);
+ return err;
+}
+
+/**
+ * fault_in_user_writeable() - Fault in user address and verify RW access
+ * @uaddr: pointer to faulting user space address
+ *
+ * Slow path to fixup the fault we just took in the atomic write
+ * access to @uaddr.
+ *
+ * We have no generic implementation of a non-destructive write to the
+ * user address. We know that we faulted in the atomic pagefault
+ * disabled section so we can as well avoid the #PF overhead by
+ * calling get_user_pages() right away.
+ */
+static int fault_in_user_writeable(u32 __user *uaddr)
+{
+ struct mm_struct *mm = current->mm;
+ int ret;
+
+ mmap_read_lock(mm);
+ ret = fixup_user_fault(mm, (unsigned long)uaddr,
+ FAULT_FLAG_WRITE, NULL);
+ mmap_read_unlock(mm);
+
+ return ret < 0 ? ret : 0;
+}
+
+/**
+ * futex_top_waiter() - Return the highest priority waiter on a futex
+ * @hb: the hash bucket the futex_q's reside in
+ * @key: the futex key (to distinguish it from other futex futex_q's)
+ *
+ * Must be called with the hb lock held.
+ */
+static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
+ union futex_key *key)
+{
+ struct futex_q *this;
+
+ plist_for_each_entry(this, &hb->chain, list) {
+ if (match_futex(&this->key, key))
+ return this;
+ }
+ return NULL;
+}
+
+static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
+ u32 uval, u32 newval)
+{
+ int ret;
+
+ pagefault_disable();
+ ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
+ pagefault_enable();
+
+ return ret;
+}
+
+static int get_futex_value_locked(u32 *dest, u32 __user *from)
+{
+ int ret;
+
+ pagefault_disable();
+ ret = __get_user(*dest, from);
+ pagefault_enable();
+
+ return ret ? -EFAULT : 0;
+}
+
+
+/*
+ * PI code:
+ */
+static int refill_pi_state_cache(void)
+{
+ struct futex_pi_state *pi_state;
+
+ if (likely(current->pi_state_cache))
+ return 0;
+
+ pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
+
+ if (!pi_state)
+ return -ENOMEM;
+
+ INIT_LIST_HEAD(&pi_state->list);
+ /* pi_mutex gets initialized later */
+ pi_state->owner = NULL;
+ refcount_set(&pi_state->refcount, 1);
+ pi_state->key = FUTEX_KEY_INIT;
+
+ current->pi_state_cache = pi_state;
+
+ return 0;
+}
+
+static struct futex_pi_state *alloc_pi_state(void)
+{
+ struct futex_pi_state *pi_state = current->pi_state_cache;
+
+ WARN_ON(!pi_state);
+ current->pi_state_cache = NULL;
+
+ return pi_state;
+}
+
+static void pi_state_update_owner(struct futex_pi_state *pi_state,
+ struct task_struct *new_owner)
+{
+ struct task_struct *old_owner = pi_state->owner;
+
+ lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
+
+ if (old_owner) {
+ raw_spin_lock(&old_owner->pi_lock);
+ WARN_ON(list_empty(&pi_state->list));
+ list_del_init(&pi_state->list);
+ raw_spin_unlock(&old_owner->pi_lock);
+ }
+
+ if (new_owner) {
+ raw_spin_lock(&new_owner->pi_lock);
+ WARN_ON(!list_empty(&pi_state->list));
+ list_add(&pi_state->list, &new_owner->pi_state_list);
+ pi_state->owner = new_owner;
+ raw_spin_unlock(&new_owner->pi_lock);
+ }
+}
+
+static void get_pi_state(struct futex_pi_state *pi_state)
+{
+ WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
+}
+
+/*
+ * Drops a reference to the pi_state object and frees or caches it
+ * when the last reference is gone.
+ */
+static void put_pi_state(struct futex_pi_state *pi_state)
+{
+ if (!pi_state)
+ return;
+
+ if (!refcount_dec_and_test(&pi_state->refcount))
+ return;
+
+ /*
+ * If pi_state->owner is NULL, the owner is most probably dying
+ * and has cleaned up the pi_state already
+ */
+ if (pi_state->owner) {
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
+ pi_state_update_owner(pi_state, NULL);
+ rt_mutex_proxy_unlock(&pi_state->pi_mutex);
+ raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
+ }
+
+ if (current->pi_state_cache) {
+ kfree(pi_state);
+ } else {
+ /*
+ * pi_state->list is already empty.
+ * clear pi_state->owner.
+ * refcount is at 0 - put it back to 1.
+ */
+ pi_state->owner = NULL;
+ refcount_set(&pi_state->refcount, 1);
+ current->pi_state_cache = pi_state;
+ }
+}
+
+#ifdef CONFIG_FUTEX_PI
+
+/*
+ * This task is holding PI mutexes at exit time => bad.
+ * Kernel cleans up PI-state, but userspace is likely hosed.
+ * (Robust-futex cleanup is separate and might save the day for userspace.)
+ */
+static void exit_pi_state_list(struct task_struct *curr)
+{
+ struct list_head *next, *head = &curr->pi_state_list;
+ struct futex_pi_state *pi_state;
+ struct futex_hash_bucket *hb;
+ union futex_key key = FUTEX_KEY_INIT;
+
+ if (!futex_cmpxchg_enabled)
+ return;
+ /*
+ * We are a ZOMBIE and nobody can enqueue itself on
+ * pi_state_list anymore, but we have to be careful
+ * versus waiters unqueueing themselves:
+ */
+ raw_spin_lock_irq(&curr->pi_lock);
+ while (!list_empty(head)) {
+ next = head->next;
+ pi_state = list_entry(next, struct futex_pi_state, list);
+ key = pi_state->key;
+ hb = hash_futex(&key);
+
+ /*
+ * We can race against put_pi_state() removing itself from the
+ * list (a waiter going away). put_pi_state() will first
+ * decrement the reference count and then modify the list, so
+ * its possible to see the list entry but fail this reference
+ * acquire.
+ *
+ * In that case; drop the locks to let put_pi_state() make
+ * progress and retry the loop.
+ */
+ if (!refcount_inc_not_zero(&pi_state->refcount)) {
+ raw_spin_unlock_irq(&curr->pi_lock);
+ cpu_relax();
+ raw_spin_lock_irq(&curr->pi_lock);
+ continue;
+ }
+ raw_spin_unlock_irq(&curr->pi_lock);
+
+ spin_lock(&hb->lock);
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+ raw_spin_lock(&curr->pi_lock);
+ /*
+ * We dropped the pi-lock, so re-check whether this
+ * task still owns the PI-state:
+ */
+ if (head->next != next) {
+ /* retain curr->pi_lock for the loop invariant */
+ raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(&hb->lock);
+ put_pi_state(pi_state);
+ continue;
+ }
+
+ WARN_ON(pi_state->owner != curr);
+ WARN_ON(list_empty(&pi_state->list));
+ list_del_init(&pi_state->list);
+ pi_state->owner = NULL;
+
+ raw_spin_unlock(&curr->pi_lock);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(&hb->lock);
+
+ rt_mutex_futex_unlock(&pi_state->pi_mutex);
+ put_pi_state(pi_state);
+
+ raw_spin_lock_irq(&curr->pi_lock);
+ }
+ raw_spin_unlock_irq(&curr->pi_lock);
+}
+#else
+static inline void exit_pi_state_list(struct task_struct *curr) { }
+#endif
+
+/*
+ * We need to check the following states:
+ *
+ * Waiter | pi_state | pi->owner | uTID | uODIED | ?
+ *
+ * [1] NULL | --- | --- | 0 | 0/1 | Valid
+ * [2] NULL | --- | --- | >0 | 0/1 | Valid
+ *
+ * [3] Found | NULL | -- | Any | 0/1 | Invalid
+ *
+ * [4] Found | Found | NULL | 0 | 1 | Valid
+ * [5] Found | Found | NULL | >0 | 1 | Invalid
+ *
+ * [6] Found | Found | task | 0 | 1 | Valid
+ *
+ * [7] Found | Found | NULL | Any | 0 | Invalid
+ *
+ * [8] Found | Found | task | ==taskTID | 0/1 | Valid
+ * [9] Found | Found | task | 0 | 0 | Invalid
+ * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
+ *
+ * [1] Indicates that the kernel can acquire the futex atomically. We
+ * came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
+ *
+ * [2] Valid, if TID does not belong to a kernel thread. If no matching
+ * thread is found then it indicates that the owner TID has died.
+ *
+ * [3] Invalid. The waiter is queued on a non PI futex
+ *
+ * [4] Valid state after exit_robust_list(), which sets the user space
+ * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
+ *
+ * [5] The user space value got manipulated between exit_robust_list()
+ * and exit_pi_state_list()
+ *
+ * [6] Valid state after exit_pi_state_list() which sets the new owner in
+ * the pi_state but cannot access the user space value.
+ *
+ * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
+ *
+ * [8] Owner and user space value match
+ *
+ * [9] There is no transient state which sets the user space TID to 0
+ * except exit_robust_list(), but this is indicated by the
+ * FUTEX_OWNER_DIED bit. See [4]
+ *
+ * [10] There is no transient state which leaves owner and user space
+ * TID out of sync. Except one error case where the kernel is denied
+ * write access to the user address, see fixup_pi_state_owner().
+ *
+ *
+ * Serialization and lifetime rules:
+ *
+ * hb->lock:
+ *
+ * hb -> futex_q, relation
+ * futex_q -> pi_state, relation
+ *
+ * (cannot be raw because hb can contain arbitrary amount
+ * of futex_q's)
+ *
+ * pi_mutex->wait_lock:
+ *
+ * {uval, pi_state}
+ *
+ * (and pi_mutex 'obviously')
+ *
+ * p->pi_lock:
+ *
+ * p->pi_state_list -> pi_state->list, relation
+ * pi_mutex->owner -> pi_state->owner, relation
+ *
+ * pi_state->refcount:
+ *
+ * pi_state lifetime
+ *
+ *
+ * Lock order:
+ *
+ * hb->lock
+ * pi_mutex->wait_lock
+ * p->pi_lock
+ *
+ */
+
+/*
+ * Validate that the existing waiter has a pi_state and sanity check
+ * the pi_state against the user space value. If correct, attach to
+ * it.
+ */
+static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
+ struct futex_pi_state *pi_state,
+ struct futex_pi_state **ps)
+{
+ pid_t pid = uval & FUTEX_TID_MASK;
+ u32 uval2;
+ int ret;
+
+ /*
+ * Userspace might have messed up non-PI and PI futexes [3]
+ */
+ if (unlikely(!pi_state))
+ return -EINVAL;
+
+ /*
+ * We get here with hb->lock held, and having found a
+ * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
+ * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
+ * which in turn means that futex_lock_pi() still has a reference on
+ * our pi_state.
+ *
+ * The waiter holding a reference on @pi_state also protects against
+ * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
+ * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
+ * free pi_state before we can take a reference ourselves.
+ */
+ WARN_ON(!refcount_read(&pi_state->refcount));
+
+ /*
+ * Now that we have a pi_state, we can acquire wait_lock
+ * and do the state validation.
+ */
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+ /*
+ * Since {uval, pi_state} is serialized by wait_lock, and our current
+ * uval was read without holding it, it can have changed. Verify it
+ * still is what we expect it to be, otherwise retry the entire
+ * operation.
+ */
+ if (get_futex_value_locked(&uval2, uaddr))
+ goto out_efault;
+
+ if (uval != uval2)
+ goto out_eagain;
+
+ /*
+ * Handle the owner died case:
+ */
+ if (uval & FUTEX_OWNER_DIED) {
+ /*
+ * exit_pi_state_list sets owner to NULL and wakes the
+ * topmost waiter. The task which acquires the
+ * pi_state->rt_mutex will fixup owner.
+ */
+ if (!pi_state->owner) {
+ /*
+ * No pi state owner, but the user space TID
+ * is not 0. Inconsistent state. [5]
+ */
+ if (pid)
+ goto out_einval;
+ /*
+ * Take a ref on the state and return success. [4]
+ */
+ goto out_attach;
+ }
+
+ /*
+ * If TID is 0, then either the dying owner has not
+ * yet executed exit_pi_state_list() or some waiter
+ * acquired the rtmutex in the pi state, but did not
+ * yet fixup the TID in user space.
+ *
+ * Take a ref on the state and return success. [6]
+ */
+ if (!pid)
+ goto out_attach;
+ } else {
+ /*
+ * If the owner died bit is not set, then the pi_state
+ * must have an owner. [7]
+ */
+ if (!pi_state->owner)
+ goto out_einval;
+ }
+
+ /*
+ * Bail out if user space manipulated the futex value. If pi
+ * state exists then the owner TID must be the same as the
+ * user space TID. [9/10]
+ */
+ if (pid != task_pid_vnr(pi_state->owner))
+ goto out_einval;
+
+out_attach:
+ get_pi_state(pi_state);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ *ps = pi_state;
+ return 0;
+
+out_einval:
+ ret = -EINVAL;
+ goto out_error;
+
+out_eagain:
+ ret = -EAGAIN;
+ goto out_error;
+
+out_efault:
+ ret = -EFAULT;
+ goto out_error;
+
+out_error:
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ return ret;
+}
+
+/**
+ * wait_for_owner_exiting - Block until the owner has exited
+ * @ret: owner's current futex lock status
+ * @exiting: Pointer to the exiting task
+ *
+ * Caller must hold a refcount on @exiting.
+ */
+static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
+{
+ if (ret != -EBUSY) {
+ WARN_ON_ONCE(exiting);
+ return;
+ }
+
+ if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
+ return;
+
+ mutex_lock(&exiting->futex_exit_mutex);
+ /*
+ * No point in doing state checking here. If the waiter got here
+ * while the task was in exec()->exec_futex_release() then it can
+ * have any FUTEX_STATE_* value when the waiter has acquired the
+ * mutex. OK, if running, EXITING or DEAD if it reached exit()
+ * already. Highly unlikely and not a problem. Just one more round
+ * through the futex maze.
+ */
+ mutex_unlock(&exiting->futex_exit_mutex);
+
+ put_task_struct(exiting);
+}
+
+static int handle_exit_race(u32 __user *uaddr, u32 uval,
+ struct task_struct *tsk)
+{
+ u32 uval2;
+
+ /*
+ * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
+ * caller that the alleged owner is busy.
+ */
+ if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
+ return -EBUSY;
+
+ /*
+ * Reread the user space value to handle the following situation:
+ *
+ * CPU0 CPU1
+ *
+ * sys_exit() sys_futex()
+ * do_exit() futex_lock_pi()
+ * futex_lock_pi_atomic()
+ * exit_signals(tsk) No waiters:
+ * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
+ * mm_release(tsk) Set waiter bit
+ * exit_robust_list(tsk) { *uaddr = 0x80000PID;
+ * Set owner died attach_to_pi_owner() {
+ * *uaddr = 0xC0000000; tsk = get_task(PID);
+ * } if (!tsk->flags & PF_EXITING) {
+ * ... attach();
+ * tsk->futex_state = } else {
+ * FUTEX_STATE_DEAD; if (tsk->futex_state !=
+ * FUTEX_STATE_DEAD)
+ * return -EAGAIN;
+ * return -ESRCH; <--- FAIL
+ * }
+ *
+ * Returning ESRCH unconditionally is wrong here because the
+ * user space value has been changed by the exiting task.
+ *
+ * The same logic applies to the case where the exiting task is
+ * already gone.
+ */
+ if (get_futex_value_locked(&uval2, uaddr))
+ return -EFAULT;
+
+ /* If the user space value has changed, try again. */
+ if (uval2 != uval)
+ return -EAGAIN;
+
+ /*
+ * The exiting task did not have a robust list, the robust list was
+ * corrupted or the user space value in *uaddr is simply bogus.
+ * Give up and tell user space.
+ */
+ return -ESRCH;
+}
+
+static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
+ struct futex_pi_state **ps)
+{
+ /*
+ * No existing pi state. First waiter. [2]
+ *
+ * This creates pi_state, we have hb->lock held, this means nothing can
+ * observe this state, wait_lock is irrelevant.
+ */
+ struct futex_pi_state *pi_state = alloc_pi_state();
+
+ /*
+ * Initialize the pi_mutex in locked state and make @p
+ * the owner of it:
+ */
+ rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
+
+ /* Store the key for possible exit cleanups: */
+ pi_state->key = *key;
+
+ WARN_ON(!list_empty(&pi_state->list));
+ list_add(&pi_state->list, &p->pi_state_list);
+ /*
+ * Assignment without holding pi_state->pi_mutex.wait_lock is safe
+ * because there is no concurrency as the object is not published yet.
+ */
+ pi_state->owner = p;
+
+ *ps = pi_state;
+}
+/*
+ * Lookup the task for the TID provided from user space and attach to
+ * it after doing proper sanity checks.
+ */
+static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
+ struct futex_pi_state **ps,
+ struct task_struct **exiting)
+{
+ pid_t pid = uval & FUTEX_TID_MASK;
+ struct task_struct *p;
+
+ /*
+ * We are the first waiter - try to look up the real owner and attach
+ * the new pi_state to it, but bail out when TID = 0 [1]
+ *
+ * The !pid check is paranoid. None of the call sites should end up
+ * with pid == 0, but better safe than sorry. Let the caller retry
+ */
+ if (!pid)
+ return -EAGAIN;
+ p = find_get_task_by_vpid(pid);
+ if (!p)
+ return handle_exit_race(uaddr, uval, NULL);
+
+ if (unlikely(p->flags & PF_KTHREAD)) {
+ put_task_struct(p);
+ return -EPERM;
+ }
+
+ /*
+ * We need to look at the task state to figure out, whether the
+ * task is exiting. To protect against the change of the task state
+ * in futex_exit_release(), we do this protected by p->pi_lock:
+ */
+ raw_spin_lock_irq(&p->pi_lock);
+ if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
+ /*
+ * The task is on the way out. When the futex state is
+ * FUTEX_STATE_DEAD, we know that the task has finished
+ * the cleanup:
+ */
+ int ret = handle_exit_race(uaddr, uval, p);
+
+ raw_spin_unlock_irq(&p->pi_lock);
+ /*
+ * If the owner task is between FUTEX_STATE_EXITING and
+ * FUTEX_STATE_DEAD then store the task pointer and keep
+ * the reference on the task struct. The calling code will
+ * drop all locks, wait for the task to reach
+ * FUTEX_STATE_DEAD and then drop the refcount. This is
+ * required to prevent a live lock when the current task
+ * preempted the exiting task between the two states.
+ */
+ if (ret == -EBUSY)
+ *exiting = p;
+ else
+ put_task_struct(p);
+ return ret;
+ }
+
+ __attach_to_pi_owner(p, key, ps);
+ raw_spin_unlock_irq(&p->pi_lock);
+
+ put_task_struct(p);
+
+ return 0;
+}
+
+static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
+{
+ int err;
+ u32 curval;
+
+ if (unlikely(should_fail_futex(true)))
+ return -EFAULT;
+
+ err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
+ if (unlikely(err))
+ return err;
+
+ /* If user space value changed, let the caller retry */
+ return curval != uval ? -EAGAIN : 0;
+}
+
+/**
+ * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
+ * @uaddr: the pi futex user address
+ * @hb: the pi futex hash bucket
+ * @key: the futex key associated with uaddr and hb
+ * @ps: the pi_state pointer where we store the result of the
+ * lookup
+ * @task: the task to perform the atomic lock work for. This will
+ * be "current" except in the case of requeue pi.
+ * @exiting: Pointer to store the task pointer of the owner task
+ * which is in the middle of exiting
+ * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Return:
+ * - 0 - ready to wait;
+ * - 1 - acquired the lock;
+ * - <0 - error
+ *
+ * The hb->lock must be held by the caller.
+ *
+ * @exiting is only set when the return value is -EBUSY. If so, this holds
+ * a refcount on the exiting task on return and the caller needs to drop it
+ * after waiting for the exit to complete.
+ */
+static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
+ union futex_key *key,
+ struct futex_pi_state **ps,
+ struct task_struct *task,
+ struct task_struct **exiting,
+ int set_waiters)
+{
+ u32 uval, newval, vpid = task_pid_vnr(task);
+ struct futex_q *top_waiter;
+ int ret;
+
+ /*
+ * Read the user space value first so we can validate a few
+ * things before proceeding further.
+ */
+ if (get_futex_value_locked(&uval, uaddr))
+ return -EFAULT;
+
+ if (unlikely(should_fail_futex(true)))
+ return -EFAULT;
+
+ /*
+ * Detect deadlocks.
+ */
+ if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
+ return -EDEADLK;
+
+ if ((unlikely(should_fail_futex(true))))
+ return -EDEADLK;
+
+ /*
+ * Lookup existing state first. If it exists, try to attach to
+ * its pi_state.
+ */
+ top_waiter = futex_top_waiter(hb, key);
+ if (top_waiter)
+ return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
+
+ /*
+ * No waiter and user TID is 0. We are here because the
+ * waiters or the owner died bit is set or called from
+ * requeue_cmp_pi or for whatever reason something took the
+ * syscall.
+ */
+ if (!(uval & FUTEX_TID_MASK)) {
+ /*
+ * We take over the futex. No other waiters and the user space
+ * TID is 0. We preserve the owner died bit.
+ */
+ newval = uval & FUTEX_OWNER_DIED;
+ newval |= vpid;
+
+ /* The futex requeue_pi code can enforce the waiters bit */
+ if (set_waiters)
+ newval |= FUTEX_WAITERS;
+
+ ret = lock_pi_update_atomic(uaddr, uval, newval);
+ if (ret)
+ return ret;
+
+ /*
+ * If the waiter bit was requested the caller also needs PI
+ * state attached to the new owner of the user space futex.
+ *
+ * @task is guaranteed to be alive and it cannot be exiting
+ * because it is either sleeping or waiting in
+ * futex_requeue_pi_wakeup_sync().
+ *
+ * No need to do the full attach_to_pi_owner() exercise
+ * because @task is known and valid.
+ */
+ if (set_waiters) {
+ raw_spin_lock_irq(&task->pi_lock);
+ __attach_to_pi_owner(task, key, ps);
+ raw_spin_unlock_irq(&task->pi_lock);
+ }
+ return 1;
+ }
+
+ /*
+ * First waiter. Set the waiters bit before attaching ourself to
+ * the owner. If owner tries to unlock, it will be forced into
+ * the kernel and blocked on hb->lock.
+ */
+ newval = uval | FUTEX_WAITERS;
+ ret = lock_pi_update_atomic(uaddr, uval, newval);
+ if (ret)
+ return ret;
+ /*
+ * If the update of the user space value succeeded, we try to
+ * attach to the owner. If that fails, no harm done, we only
+ * set the FUTEX_WAITERS bit in the user space variable.
+ */
+ return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
+}
+
+/**
+ * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
+ * @q: The futex_q to unqueue
+ *
+ * The q->lock_ptr must not be NULL and must be held by the caller.
+ */
+static void __unqueue_futex(struct futex_q *q)
+{
+ struct futex_hash_bucket *hb;
+
+ if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
+ return;
+ lockdep_assert_held(q->lock_ptr);
+
+ hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
+ plist_del(&q->list, &hb->chain);
+ hb_waiters_dec(hb);
+}
+
+/*
+ * The hash bucket lock must be held when this is called.
+ * Afterwards, the futex_q must not be accessed. Callers
+ * must ensure to later call wake_up_q() for the actual
+ * wakeups to occur.
+ */
+static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
+{
+ struct task_struct *p = q->task;
+
+ if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
+ return;
+
+ get_task_struct(p);
+ __unqueue_futex(q);
+ /*
+ * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
+ * is written, without taking any locks. This is possible in the event
+ * of a spurious wakeup, for example. A memory barrier is required here
+ * to prevent the following store to lock_ptr from getting ahead of the
+ * plist_del in __unqueue_futex().
+ */
+ smp_store_release(&q->lock_ptr, NULL);
+
+ /*
+ * Queue the task for later wakeup for after we've released
+ * the hb->lock.
+ */
+ wake_q_add_safe(wake_q, p);
+}
+
+/*
+ * Caller must hold a reference on @pi_state.
+ */
+static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
+{
+ struct rt_mutex_waiter *top_waiter;
+ struct task_struct *new_owner;
+ bool postunlock = false;
+ DEFINE_RT_WAKE_Q(wqh);
+ u32 curval, newval;
+ int ret = 0;
+
+ top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
+ if (WARN_ON_ONCE(!top_waiter)) {
+ /*
+ * As per the comment in futex_unlock_pi() this should not happen.
+ *
+ * When this happens, give up our locks and try again, giving
+ * the futex_lock_pi() instance time to complete, either by
+ * waiting on the rtmutex or removing itself from the futex
+ * queue.
+ */
+ ret = -EAGAIN;
+ goto out_unlock;
+ }
+
+ new_owner = top_waiter->task;
+
+ /*
+ * We pass it to the next owner. The WAITERS bit is always kept
+ * enabled while there is PI state around. We cleanup the owner
+ * died bit, because we are the owner.
+ */
+ newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
+
+ if (unlikely(should_fail_futex(true))) {
+ ret = -EFAULT;
+ goto out_unlock;
+ }
+
+ ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
+ if (!ret && (curval != uval)) {
+ /*
+ * If a unconditional UNLOCK_PI operation (user space did not
+ * try the TID->0 transition) raced with a waiter setting the
+ * FUTEX_WAITERS flag between get_user() and locking the hash
+ * bucket lock, retry the operation.
+ */
+ if ((FUTEX_TID_MASK & curval) == uval)
+ ret = -EAGAIN;
+ else
+ ret = -EINVAL;
+ }
+
+ if (!ret) {
+ /*
+ * This is a point of no return; once we modified the uval
+ * there is no going back and subsequent operations must
+ * not fail.
+ */
+ pi_state_update_owner(pi_state, new_owner);
+ postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
+ }
+
+out_unlock:
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+
+ if (postunlock)
+ rt_mutex_postunlock(&wqh);
+
+ return ret;
+}
+
+/*
+ * Express the locking dependencies for lockdep:
+ */
+static inline void
+double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
+{
+ if (hb1 <= hb2) {
+ spin_lock(&hb1->lock);
+ if (hb1 < hb2)
+ spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
+ } else { /* hb1 > hb2 */
+ spin_lock(&hb2->lock);
+ spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
+ }
+}
+
+static inline void
+double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
+{
+ spin_unlock(&hb1->lock);
+ if (hb1 != hb2)
+ spin_unlock(&hb2->lock);
+}
+
+/*
+ * Wake up waiters matching bitset queued on this futex (uaddr).
+ */
+static int
+futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
+{
+ struct futex_hash_bucket *hb;
+ struct futex_q *this, *next;
+ union futex_key key = FUTEX_KEY_INIT;
+ int ret;
+ DEFINE_WAKE_Q(wake_q);
+
+ if (!bitset)
+ return -EINVAL;
+
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
+ if (unlikely(ret != 0))
+ return ret;
+
+ hb = hash_futex(&key);
+
+ /* Make sure we really have tasks to wakeup */
+ if (!hb_waiters_pending(hb))
+ return ret;
+
+ spin_lock(&hb->lock);
+
+ plist_for_each_entry_safe(this, next, &hb->chain, list) {
+ if (match_futex (&this->key, &key)) {
+ if (this->pi_state || this->rt_waiter) {
+ ret = -EINVAL;
+ break;
+ }
+
+ /* Check if one of the bits is set in both bitsets */
+ if (!(this->bitset & bitset))
+ continue;
+
+ mark_wake_futex(&wake_q, this);
+ if (++ret >= nr_wake)
+ break;
+ }
+ }
+
+ spin_unlock(&hb->lock);
+ wake_up_q(&wake_q);
+ return ret;
+}
+
+static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
+{
+ unsigned int op = (encoded_op & 0x70000000) >> 28;
+ unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
+ int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
+ int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
+ int oldval, ret;
+
+ if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
+ if (oparg < 0 || oparg > 31) {
+ char comm[sizeof(current->comm)];
+ /*
+ * kill this print and return -EINVAL when userspace
+ * is sane again
+ */
+ pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
+ get_task_comm(comm, current), oparg);
+ oparg &= 31;
+ }
+ oparg = 1 << oparg;
+ }
+
+ pagefault_disable();
+ ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
+ pagefault_enable();
+ if (ret)
+ return ret;
+
+ switch (cmp) {
+ case FUTEX_OP_CMP_EQ:
+ return oldval == cmparg;
+ case FUTEX_OP_CMP_NE:
+ return oldval != cmparg;
+ case FUTEX_OP_CMP_LT:
+ return oldval < cmparg;
+ case FUTEX_OP_CMP_GE:
+ return oldval >= cmparg;
+ case FUTEX_OP_CMP_LE:
+ return oldval <= cmparg;
+ case FUTEX_OP_CMP_GT:
+ return oldval > cmparg;
+ default:
+ return -ENOSYS;
+ }
+}
+
+/*
+ * Wake up all waiters hashed on the physical page that is mapped
+ * to this virtual address:
+ */
+static int
+futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
+ int nr_wake, int nr_wake2, int op)
+{
+ union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
+ struct futex_hash_bucket *hb1, *hb2;
+ struct futex_q *this, *next;
+ int ret, op_ret;
+ DEFINE_WAKE_Q(wake_q);
+
+retry:
+ ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
+ if (unlikely(ret != 0))
+ return ret;
+ ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
+ if (unlikely(ret != 0))
+ return ret;
+
+ hb1 = hash_futex(&key1);
+ hb2 = hash_futex(&key2);
+
+retry_private:
+ double_lock_hb(hb1, hb2);
+ op_ret = futex_atomic_op_inuser(op, uaddr2);
+ if (unlikely(op_ret < 0)) {
+ double_unlock_hb(hb1, hb2);
+
+ if (!IS_ENABLED(CONFIG_MMU) ||
+ unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
+ /*
+ * we don't get EFAULT from MMU faults if we don't have
+ * an MMU, but we might get them from range checking
+ */
+ ret = op_ret;
+ return ret;
+ }
+
+ if (op_ret == -EFAULT) {
+ ret = fault_in_user_writeable(uaddr2);
+ if (ret)
+ return ret;
+ }
+
+ cond_resched();
+ if (!(flags & FLAGS_SHARED))
+ goto retry_private;
+ goto retry;
+ }
+
+ plist_for_each_entry_safe(this, next, &hb1->chain, list) {
+ if (match_futex (&this->key, &key1)) {
+ if (this->pi_state || this->rt_waiter) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+ mark_wake_futex(&wake_q, this);
+ if (++ret >= nr_wake)
+ break;
+ }
+ }
+
+ if (op_ret > 0) {
+ op_ret = 0;
+ plist_for_each_entry_safe(this, next, &hb2->chain, list) {
+ if (match_futex (&this->key, &key2)) {
+ if (this->pi_state || this->rt_waiter) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+ mark_wake_futex(&wake_q, this);
+ if (++op_ret >= nr_wake2)
+ break;
+ }
+ }
+ ret += op_ret;
+ }
+
+out_unlock:
+ double_unlock_hb(hb1, hb2);
+ wake_up_q(&wake_q);
+ return ret;
+}
+
+/**
+ * requeue_futex() - Requeue a futex_q from one hb to another
+ * @q: the futex_q to requeue
+ * @hb1: the source hash_bucket
+ * @hb2: the target hash_bucket
+ * @key2: the new key for the requeued futex_q
+ */
+static inline
+void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
+ struct futex_hash_bucket *hb2, union futex_key *key2)
+{
+
+ /*
+ * If key1 and key2 hash to the same bucket, no need to
+ * requeue.
+ */
+ if (likely(&hb1->chain != &hb2->chain)) {
+ plist_del(&q->list, &hb1->chain);
+ hb_waiters_dec(hb1);
+ hb_waiters_inc(hb2);
+ plist_add(&q->list, &hb2->chain);
+ q->lock_ptr = &hb2->lock;
+ }
+ q->key = *key2;
+}
+
+static inline bool futex_requeue_pi_prepare(struct futex_q *q,
+ struct futex_pi_state *pi_state)
+{
+ int old, new;
+
+ /*
+ * Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has
+ * already set Q_REQUEUE_PI_IGNORE to signal that requeue should
+ * ignore the waiter.
+ */
+ old = atomic_read_acquire(&q->requeue_state);
+ do {
+ if (old == Q_REQUEUE_PI_IGNORE)
+ return false;
+
+ /*
+ * futex_proxy_trylock_atomic() might have set it to
+ * IN_PROGRESS and a interleaved early wake to WAIT.
+ *
+ * It was considered to have an extra state for that
+ * trylock, but that would just add more conditionals
+ * all over the place for a dubious value.
+ */
+ if (old != Q_REQUEUE_PI_NONE)
+ break;
+
+ new = Q_REQUEUE_PI_IN_PROGRESS;
+ } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
+
+ q->pi_state = pi_state;
+ return true;
+}
+
+static inline void futex_requeue_pi_complete(struct futex_q *q, int locked)
+{
+ int old, new;
+
+ old = atomic_read_acquire(&q->requeue_state);
+ do {
+ if (old == Q_REQUEUE_PI_IGNORE)
+ return;
+
+ if (locked >= 0) {
+ /* Requeue succeeded. Set DONE or LOCKED */
+ WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS &&
+ old != Q_REQUEUE_PI_WAIT);
+ new = Q_REQUEUE_PI_DONE + locked;
+ } else if (old == Q_REQUEUE_PI_IN_PROGRESS) {
+ /* Deadlock, no early wakeup interleave */
+ new = Q_REQUEUE_PI_NONE;
+ } else {
+ /* Deadlock, early wakeup interleave. */
+ WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT);
+ new = Q_REQUEUE_PI_IGNORE;
+ }
+ } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
+
+#ifdef CONFIG_PREEMPT_RT
+ /* If the waiter interleaved with the requeue let it know */
+ if (unlikely(old == Q_REQUEUE_PI_WAIT))
+ rcuwait_wake_up(&q->requeue_wait);
+#endif
+}
+
+static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
+{
+ int old, new;
+
+ old = atomic_read_acquire(&q->requeue_state);
+ do {
+ /* Is requeue done already? */
+ if (old >= Q_REQUEUE_PI_DONE)
+ return old;
+
+ /*
+ * If not done, then tell the requeue code to either ignore
+ * the waiter or to wake it up once the requeue is done.
+ */
+ new = Q_REQUEUE_PI_WAIT;
+ if (old == Q_REQUEUE_PI_NONE)
+ new = Q_REQUEUE_PI_IGNORE;
+ } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
+
+ /* If the requeue was in progress, wait for it to complete */
+ if (old == Q_REQUEUE_PI_IN_PROGRESS) {
+#ifdef CONFIG_PREEMPT_RT
+ rcuwait_wait_event(&q->requeue_wait,
+ atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT,
+ TASK_UNINTERRUPTIBLE);
+#else
+ (void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT);
+#endif
+ }
+
+ /*
+ * Requeue is now either prohibited or complete. Reread state
+ * because during the wait above it might have changed. Nothing
+ * will modify q->requeue_state after this point.
+ */
+ return atomic_read(&q->requeue_state);
+}
+
+/**
+ * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
+ * @q: the futex_q
+ * @key: the key of the requeue target futex
+ * @hb: the hash_bucket of the requeue target futex
+ *
+ * During futex_requeue, with requeue_pi=1, it is possible to acquire the
+ * target futex if it is uncontended or via a lock steal.
+ *
+ * 1) Set @q::key to the requeue target futex key so the waiter can detect
+ * the wakeup on the right futex.
+ *
+ * 2) Dequeue @q from the hash bucket.
+ *
+ * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock
+ * acquisition.
+ *
+ * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that
+ * the waiter has to fixup the pi state.
+ *
+ * 5) Complete the requeue state so the waiter can make progress. After
+ * this point the waiter task can return from the syscall immediately in
+ * case that the pi state does not have to be fixed up.
+ *
+ * 6) Wake the waiter task.
+ *
+ * Must be called with both q->lock_ptr and hb->lock held.
+ */
+static inline
+void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
+ struct futex_hash_bucket *hb)
+{
+ q->key = *key;
+
+ __unqueue_futex(q);
+
+ WARN_ON(!q->rt_waiter);
+ q->rt_waiter = NULL;
+
+ q->lock_ptr = &hb->lock;
+
+ /* Signal locked state to the waiter */
+ futex_requeue_pi_complete(q, 1);
+ wake_up_state(q->task, TASK_NORMAL);
+}
+
+/**
+ * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
+ * @pifutex: the user address of the to futex
+ * @hb1: the from futex hash bucket, must be locked by the caller
+ * @hb2: the to futex hash bucket, must be locked by the caller
+ * @key1: the from futex key
+ * @key2: the to futex key
+ * @ps: address to store the pi_state pointer
+ * @exiting: Pointer to store the task pointer of the owner task
+ * which is in the middle of exiting
+ * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Try and get the lock on behalf of the top waiter if we can do it atomically.
+ * Wake the top waiter if we succeed. If the caller specified set_waiters,
+ * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
+ * hb1 and hb2 must be held by the caller.
+ *
+ * @exiting is only set when the return value is -EBUSY. If so, this holds
+ * a refcount on the exiting task on return and the caller needs to drop it
+ * after waiting for the exit to complete.
+ *
+ * Return:
+ * - 0 - failed to acquire the lock atomically;
+ * - >0 - acquired the lock, return value is vpid of the top_waiter
+ * - <0 - error
+ */
+static int
+futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
+ struct futex_hash_bucket *hb2, union futex_key *key1,
+ union futex_key *key2, struct futex_pi_state **ps,
+ struct task_struct **exiting, int set_waiters)
+{
+ struct futex_q *top_waiter = NULL;
+ u32 curval;
+ int ret;
+
+ if (get_futex_value_locked(&curval, pifutex))
+ return -EFAULT;
+
+ if (unlikely(should_fail_futex(true)))
+ return -EFAULT;
+
+ /*
+ * Find the top_waiter and determine if there are additional waiters.
+ * If the caller intends to requeue more than 1 waiter to pifutex,
+ * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
+ * as we have means to handle the possible fault. If not, don't set
+ * the bit unnecessarily as it will force the subsequent unlock to enter
+ * the kernel.
+ */
+ top_waiter = futex_top_waiter(hb1, key1);
+
+ /* There are no waiters, nothing for us to do. */
+ if (!top_waiter)
+ return 0;
+
+ /*
+ * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
+ * and waiting on the 'waitqueue' futex which is always !PI.
+ */
+ if (!top_waiter->rt_waiter || top_waiter->pi_state)
+ return -EINVAL;
+
+ /* Ensure we requeue to the expected futex. */
+ if (!match_futex(top_waiter->requeue_pi_key, key2))
+ return -EINVAL;
+
+ /* Ensure that this does not race against an early wakeup */
+ if (!futex_requeue_pi_prepare(top_waiter, NULL))
+ return -EAGAIN;
+
+ /*
+ * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
+ * in the contended case or if @set_waiters is true.
+ *
+ * In the contended case PI state is attached to the lock owner. If
+ * the user space lock can be acquired then PI state is attached to
+ * the new owner (@top_waiter->task) when @set_waiters is true.
+ */
+ ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
+ exiting, set_waiters);
+ if (ret == 1) {
+ /*
+ * Lock was acquired in user space and PI state was
+ * attached to @top_waiter->task. That means state is fully
+ * consistent and the waiter can return to user space
+ * immediately after the wakeup.
+ */
+ requeue_pi_wake_futex(top_waiter, key2, hb2);
+ } else if (ret < 0) {
+ /* Rewind top_waiter::requeue_state */
+ futex_requeue_pi_complete(top_waiter, ret);
+ } else {
+ /*
+ * futex_lock_pi_atomic() did not acquire the user space
+ * futex, but managed to establish the proxy lock and pi
+ * state. top_waiter::requeue_state cannot be fixed up here
+ * because the waiter is not enqueued on the rtmutex
+ * yet. This is handled at the callsite depending on the
+ * result of rt_mutex_start_proxy_lock() which is
+ * guaranteed to be reached with this function returning 0.
+ */
+ }
+ return ret;
+}
+
+/**
+ * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
+ * @uaddr1: source futex user address
+ * @flags: futex flags (FLAGS_SHARED, etc.)
+ * @uaddr2: target futex user address
+ * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
+ * @nr_requeue: number of waiters to requeue (0-INT_MAX)
+ * @cmpval: @uaddr1 expected value (or %NULL)
+ * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
+ * pi futex (pi to pi requeue is not supported)
+ *
+ * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
+ * uaddr2 atomically on behalf of the top waiter.
+ *
+ * Return:
+ * - >=0 - on success, the number of tasks requeued or woken;
+ * - <0 - on error
+ */
+static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+ u32 __user *uaddr2, int nr_wake, int nr_requeue,
+ u32 *cmpval, int requeue_pi)
+{
+ union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
+ int task_count = 0, ret;
+ struct futex_pi_state *pi_state = NULL;
+ struct futex_hash_bucket *hb1, *hb2;
+ struct futex_q *this, *next;
+ DEFINE_WAKE_Q(wake_q);
+
+ if (nr_wake < 0 || nr_requeue < 0)
+ return -EINVAL;
+
+ /*
+ * When PI not supported: return -ENOSYS if requeue_pi is true,
+ * consequently the compiler knows requeue_pi is always false past
+ * this point which will optimize away all the conditional code
+ * further down.
+ */
+ if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
+ return -ENOSYS;
+
+ if (requeue_pi) {
+ /*
+ * Requeue PI only works on two distinct uaddrs. This
+ * check is only valid for private futexes. See below.
+ */
+ if (uaddr1 == uaddr2)
+ return -EINVAL;
+
+ /*
+ * futex_requeue() allows the caller to define the number
+ * of waiters to wake up via the @nr_wake argument. With
+ * REQUEUE_PI, waking up more than one waiter is creating
+ * more problems than it solves. Waking up a waiter makes
+ * only sense if the PI futex @uaddr2 is uncontended as
+ * this allows the requeue code to acquire the futex
+ * @uaddr2 before waking the waiter. The waiter can then
+ * return to user space without further action. A secondary
+ * wakeup would just make the futex_wait_requeue_pi()
+ * handling more complex, because that code would have to
+ * look up pi_state and do more or less all the handling
+ * which the requeue code has to do for the to be requeued
+ * waiters. So restrict the number of waiters to wake to
+ * one, and only wake it up when the PI futex is
+ * uncontended. Otherwise requeue it and let the unlock of
+ * the PI futex handle the wakeup.
+ *
+ * All REQUEUE_PI users, e.g. pthread_cond_signal() and
+ * pthread_cond_broadcast() must use nr_wake=1.
+ */
+ if (nr_wake != 1)
+ return -EINVAL;
+
+ /*
+ * requeue_pi requires a pi_state, try to allocate it now
+ * without any locks in case it fails.
+ */
+ if (refill_pi_state_cache())
+ return -ENOMEM;
+ }
+
+retry:
+ ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
+ if (unlikely(ret != 0))
+ return ret;
+ ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
+ requeue_pi ? FUTEX_WRITE : FUTEX_READ);
+ if (unlikely(ret != 0))
+ return ret;
+
+ /*
+ * The check above which compares uaddrs is not sufficient for
+ * shared futexes. We need to compare the keys:
+ */
+ if (requeue_pi && match_futex(&key1, &key2))
+ return -EINVAL;
+
+ hb1 = hash_futex(&key1);
+ hb2 = hash_futex(&key2);
+
+retry_private:
+ hb_waiters_inc(hb2);
+ double_lock_hb(hb1, hb2);
+
+ if (likely(cmpval != NULL)) {
+ u32 curval;
+
+ ret = get_futex_value_locked(&curval, uaddr1);
+
+ if (unlikely(ret)) {
+ double_unlock_hb(hb1, hb2);
+ hb_waiters_dec(hb2);
+
+ ret = get_user(curval, uaddr1);
+ if (ret)
+ return ret;
+
+ if (!(flags & FLAGS_SHARED))
+ goto retry_private;
+
+ goto retry;
+ }
+ if (curval != *cmpval) {
+ ret = -EAGAIN;
+ goto out_unlock;
+ }
+ }
+
+ if (requeue_pi) {
+ struct task_struct *exiting = NULL;
+
+ /*
+ * Attempt to acquire uaddr2 and wake the top waiter. If we
+ * intend to requeue waiters, force setting the FUTEX_WAITERS
+ * bit. We force this here where we are able to easily handle
+ * faults rather in the requeue loop below.
+ *
+ * Updates topwaiter::requeue_state if a top waiter exists.
+ */
+ ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
+ &key2, &pi_state,
+ &exiting, nr_requeue);
+
+ /*
+ * At this point the top_waiter has either taken uaddr2 or
+ * is waiting on it. In both cases pi_state has been
+ * established and an initial refcount on it. In case of an
+ * error there's nothing.
+ *
+ * The top waiter's requeue_state is up to date:
+ *
+ * - If the lock was acquired atomically (ret == 1), then
+ * the state is Q_REQUEUE_PI_LOCKED.
+ *
+ * The top waiter has been dequeued and woken up and can
+ * return to user space immediately. The kernel/user
+ * space state is consistent. In case that there must be
+ * more waiters requeued the WAITERS bit in the user
+ * space futex is set so the top waiter task has to go
+ * into the syscall slowpath to unlock the futex. This
+ * will block until this requeue operation has been
+ * completed and the hash bucket locks have been
+ * dropped.
+ *
+ * - If the trylock failed with an error (ret < 0) then
+ * the state is either Q_REQUEUE_PI_NONE, i.e. "nothing
+ * happened", or Q_REQUEUE_PI_IGNORE when there was an
+ * interleaved early wakeup.
+ *
+ * - If the trylock did not succeed (ret == 0) then the
+ * state is either Q_REQUEUE_PI_IN_PROGRESS or
+ * Q_REQUEUE_PI_WAIT if an early wakeup interleaved.
+ * This will be cleaned up in the loop below, which
+ * cannot fail because futex_proxy_trylock_atomic() did
+ * the same sanity checks for requeue_pi as the loop
+ * below does.
+ */
+ switch (ret) {
+ case 0:
+ /* We hold a reference on the pi state. */
+ break;
+
+ case 1:
+ /*
+ * futex_proxy_trylock_atomic() acquired the user space
+ * futex. Adjust task_count.
+ */
+ task_count++;
+ ret = 0;
+ break;
+
+ /*
+ * If the above failed, then pi_state is NULL and
+ * waiter::requeue_state is correct.
+ */
+ case -EFAULT:
+ double_unlock_hb(hb1, hb2);
+ hb_waiters_dec(hb2);
+ ret = fault_in_user_writeable(uaddr2);
+ if (!ret)
+ goto retry;
+ return ret;
+ case -EBUSY:
+ case -EAGAIN:
+ /*
+ * Two reasons for this:
+ * - EBUSY: Owner is exiting and we just wait for the
+ * exit to complete.
+ * - EAGAIN: The user space value changed.
+ */
+ double_unlock_hb(hb1, hb2);
+ hb_waiters_dec(hb2);
+ /*
+ * Handle the case where the owner is in the middle of
+ * exiting. Wait for the exit to complete otherwise
+ * this task might loop forever, aka. live lock.
+ */
+ wait_for_owner_exiting(ret, exiting);
+ cond_resched();
+ goto retry;
+ default:
+ goto out_unlock;
+ }
+ }
+
+ plist_for_each_entry_safe(this, next, &hb1->chain, list) {
+ if (task_count - nr_wake >= nr_requeue)
+ break;
+
+ if (!match_futex(&this->key, &key1))
+ continue;
+
+ /*
+ * FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always
+ * be paired with each other and no other futex ops.
+ *
+ * We should never be requeueing a futex_q with a pi_state,
+ * which is awaiting a futex_unlock_pi().
+ */
+ if ((requeue_pi && !this->rt_waiter) ||
+ (!requeue_pi && this->rt_waiter) ||
+ this->pi_state) {
+ ret = -EINVAL;
+ break;
+ }
+
+ /* Plain futexes just wake or requeue and are done */
+ if (!requeue_pi) {
+ if (++task_count <= nr_wake)
+ mark_wake_futex(&wake_q, this);
+ else
+ requeue_futex(this, hb1, hb2, &key2);
+ continue;
+ }
+
+ /* Ensure we requeue to the expected futex for requeue_pi. */
+ if (!match_futex(this->requeue_pi_key, &key2)) {
+ ret = -EINVAL;
+ break;
+ }
+
+ /*
+ * Requeue nr_requeue waiters and possibly one more in the case
+ * of requeue_pi if we couldn't acquire the lock atomically.
+ *
+ * Prepare the waiter to take the rt_mutex. Take a refcount
+ * on the pi_state and store the pointer in the futex_q
+ * object of the waiter.
+ */
+ get_pi_state(pi_state);
+
+ /* Don't requeue when the waiter is already on the way out. */
+ if (!futex_requeue_pi_prepare(this, pi_state)) {
+ /*
+ * Early woken waiter signaled that it is on the
+ * way out. Drop the pi_state reference and try the
+ * next waiter. @this->pi_state is still NULL.
+ */
+ put_pi_state(pi_state);
+ continue;
+ }
+
+ ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
+ this->rt_waiter,
+ this->task);
+
+ if (ret == 1) {
+ /*
+ * We got the lock. We do neither drop the refcount
+ * on pi_state nor clear this->pi_state because the
+ * waiter needs the pi_state for cleaning up the
+ * user space value. It will drop the refcount
+ * after doing so. this::requeue_state is updated
+ * in the wakeup as well.
+ */
+ requeue_pi_wake_futex(this, &key2, hb2);
+ task_count++;
+ } else if (!ret) {
+ /* Waiter is queued, move it to hb2 */
+ requeue_futex(this, hb1, hb2, &key2);
+ futex_requeue_pi_complete(this, 0);
+ task_count++;
+ } else {
+ /*
+ * rt_mutex_start_proxy_lock() detected a potential
+ * deadlock when we tried to queue that waiter.
+ * Drop the pi_state reference which we took above
+ * and remove the pointer to the state from the
+ * waiters futex_q object.
+ */
+ this->pi_state = NULL;
+ put_pi_state(pi_state);
+ futex_requeue_pi_complete(this, ret);
+ /*
+ * We stop queueing more waiters and let user space
+ * deal with the mess.
+ */
+ break;
+ }
+ }
+
+ /*
+ * We took an extra initial reference to the pi_state in
+ * futex_proxy_trylock_atomic(). We need to drop it here again.
+ */
+ put_pi_state(pi_state);
+
+out_unlock:
+ double_unlock_hb(hb1, hb2);
+ wake_up_q(&wake_q);
+ hb_waiters_dec(hb2);
+ return ret ? ret : task_count;
+}
+
+/* The key must be already stored in q->key. */
+static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
+ __acquires(&hb->lock)
+{
+ struct futex_hash_bucket *hb;
+
+ hb = hash_futex(&q->key);
+
+ /*
+ * Increment the counter before taking the lock so that
+ * a potential waker won't miss a to-be-slept task that is
+ * waiting for the spinlock. This is safe as all queue_lock()
+ * users end up calling queue_me(). Similarly, for housekeeping,
+ * decrement the counter at queue_unlock() when some error has
+ * occurred and we don't end up adding the task to the list.
+ */
+ hb_waiters_inc(hb); /* implies smp_mb(); (A) */
+
+ q->lock_ptr = &hb->lock;
+
+ spin_lock(&hb->lock);
+ return hb;
+}
+
+static inline void
+queue_unlock(struct futex_hash_bucket *hb)
+ __releases(&hb->lock)
+{
+ spin_unlock(&hb->lock);
+ hb_waiters_dec(hb);
+}
+
+static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+{
+ int prio;
+
+ /*
+ * The priority used to register this element is
+ * - either the real thread-priority for the real-time threads
+ * (i.e. threads with a priority lower than MAX_RT_PRIO)
+ * - or MAX_RT_PRIO for non-RT threads.
+ * Thus, all RT-threads are woken first in priority order, and
+ * the others are woken last, in FIFO order.
+ */
+ prio = min(current->normal_prio, MAX_RT_PRIO);
+
+ plist_node_init(&q->list, prio);
+ plist_add(&q->list, &hb->chain);
+ q->task = current;
+}
+
+/**
+ * queue_me() - Enqueue the futex_q on the futex_hash_bucket
+ * @q: The futex_q to enqueue
+ * @hb: The destination hash bucket
+ *
+ * The hb->lock must be held by the caller, and is released here. A call to
+ * queue_me() is typically paired with exactly one call to unqueue_me(). The
+ * exceptions involve the PI related operations, which may use unqueue_me_pi()
+ * or nothing if the unqueue is done as part of the wake process and the unqueue
+ * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
+ * an example).
+ */
+static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+ __releases(&hb->lock)
+{
+ __queue_me(q, hb);
+ spin_unlock(&hb->lock);
+}
+
+/**
+ * unqueue_me() - Remove the futex_q from its futex_hash_bucket
+ * @q: The futex_q to unqueue
+ *
+ * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
+ * be paired with exactly one earlier call to queue_me().
+ *
+ * Return:
+ * - 1 - if the futex_q was still queued (and we removed unqueued it);
+ * - 0 - if the futex_q was already removed by the waking thread
+ */
+static int unqueue_me(struct futex_q *q)
+{
+ spinlock_t *lock_ptr;
+ int ret = 0;
+
+ /* In the common case we don't take the spinlock, which is nice. */
+retry:
+ /*
+ * q->lock_ptr can change between this read and the following spin_lock.
+ * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
+ * optimizing lock_ptr out of the logic below.
+ */
+ lock_ptr = READ_ONCE(q->lock_ptr);
+ if (lock_ptr != NULL) {
+ spin_lock(lock_ptr);
+ /*
+ * q->lock_ptr can change between reading it and
+ * spin_lock(), causing us to take the wrong lock. This
+ * corrects the race condition.
+ *
+ * Reasoning goes like this: if we have the wrong lock,
+ * q->lock_ptr must have changed (maybe several times)
+ * between reading it and the spin_lock(). It can
+ * change again after the spin_lock() but only if it was
+ * already changed before the spin_lock(). It cannot,
+ * however, change back to the original value. Therefore
+ * we can detect whether we acquired the correct lock.
+ */
+ if (unlikely(lock_ptr != q->lock_ptr)) {
+ spin_unlock(lock_ptr);
+ goto retry;
+ }
+ __unqueue_futex(q);
+
+ BUG_ON(q->pi_state);
+
+ spin_unlock(lock_ptr);
+ ret = 1;
+ }
+
+ return ret;
+}
+
+/*
+ * PI futexes can not be requeued and must remove themselves from the
+ * hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
+ */
+static void unqueue_me_pi(struct futex_q *q)
+{
+ __unqueue_futex(q);
+
+ BUG_ON(!q->pi_state);
+ put_pi_state(q->pi_state);
+ q->pi_state = NULL;
+}
+
+static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+ struct task_struct *argowner)
+{
+ struct futex_pi_state *pi_state = q->pi_state;
+ struct task_struct *oldowner, *newowner;
+ u32 uval, curval, newval, newtid;
+ int err = 0;
+
+ oldowner = pi_state->owner;
+
+ /*
+ * We are here because either:
+ *
+ * - we stole the lock and pi_state->owner needs updating to reflect
+ * that (@argowner == current),
+ *
+ * or:
+ *
+ * - someone stole our lock and we need to fix things to point to the
+ * new owner (@argowner == NULL).
+ *
+ * Either way, we have to replace the TID in the user space variable.
+ * This must be atomic as we have to preserve the owner died bit here.
+ *
+ * Note: We write the user space value _before_ changing the pi_state
+ * because we can fault here. Imagine swapped out pages or a fork
+ * that marked all the anonymous memory readonly for cow.
+ *
+ * Modifying pi_state _before_ the user space value would leave the
+ * pi_state in an inconsistent state when we fault here, because we
+ * need to drop the locks to handle the fault. This might be observed
+ * in the PID checks when attaching to PI state .
+ */
+retry:
+ if (!argowner) {
+ if (oldowner != current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ return 0;
+ }
+
+ if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
+ /* We got the lock. pi_state is correct. Tell caller. */
+ return 1;
+ }
+
+ /*
+ * The trylock just failed, so either there is an owner or
+ * there is a higher priority waiter than this one.
+ */
+ newowner = rt_mutex_owner(&pi_state->pi_mutex);
+ /*
+ * If the higher priority waiter has not yet taken over the
+ * rtmutex then newowner is NULL. We can't return here with
+ * that state because it's inconsistent vs. the user space
+ * state. So drop the locks and try again. It's a valid
+ * situation and not any different from the other retry
+ * conditions.
+ */
+ if (unlikely(!newowner)) {
+ err = -EAGAIN;
+ goto handle_err;
+ }
+ } else {
+ WARN_ON_ONCE(argowner != current);
+ if (oldowner == current) {
+ /*
+ * We raced against a concurrent self; things are
+ * already fixed up. Nothing to do.
+ */
+ return 1;
+ }
+ newowner = argowner;
+ }
+
+ newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+ /* Owner died? */
+ if (!pi_state->owner)
+ newtid |= FUTEX_OWNER_DIED;
+
+ err = get_futex_value_locked(&uval, uaddr);
+ if (err)
+ goto handle_err;
+
+ for (;;) {
+ newval = (uval & FUTEX_OWNER_DIED) | newtid;
+
+ err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
+ if (err)
+ goto handle_err;
+
+ if (curval == uval)
+ break;
+ uval = curval;
+ }
+
+ /*
+ * We fixed up user space. Now we need to fix the pi_state
+ * itself.
+ */
+ pi_state_update_owner(pi_state, newowner);
+
+ return argowner == current;
+
+ /*
+ * In order to reschedule or handle a page fault, we need to drop the
+ * locks here. In the case of a fault, this gives the other task
+ * (either the highest priority waiter itself or the task which stole
+ * the rtmutex) the chance to try the fixup of the pi_state. So once we
+ * are back from handling the fault we need to check the pi_state after
+ * reacquiring the locks and before trying to do another fixup. When
+ * the fixup has been done already we simply return.
+ *
+ * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
+ * drop hb->lock since the caller owns the hb -> futex_q relation.
+ * Dropping the pi_mutex->wait_lock requires the state revalidate.
+ */
+handle_err:
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(q->lock_ptr);
+
+ switch (err) {
+ case -EFAULT:
+ err = fault_in_user_writeable(uaddr);
+ break;
+
+ case -EAGAIN:
+ cond_resched();
+ err = 0;
+ break;
+
+ default:
+ WARN_ON_ONCE(1);
+ break;
+ }
+
+ spin_lock(q->lock_ptr);
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+ /*
+ * Check if someone else fixed it for us:
+ */
+ if (pi_state->owner != oldowner)
+ return argowner == current;
+
+ /* Retry if err was -EAGAIN or the fault in succeeded */
+ if (!err)
+ goto retry;
+
+ /*
+ * fault_in_user_writeable() failed so user state is immutable. At
+ * best we can make the kernel state consistent but user state will
+ * be most likely hosed and any subsequent unlock operation will be
+ * rejected due to PI futex rule [10].
+ *
+ * Ensure that the rtmutex owner is also the pi_state owner despite
+ * the user space value claiming something different. There is no
+ * point in unlocking the rtmutex if current is the owner as it
+ * would need to wait until the next waiter has taken the rtmutex
+ * to guarantee consistent state. Keep it simple. Userspace asked
+ * for this wreckaged state.
+ *
+ * The rtmutex has an owner - either current or some other
+ * task. See the EAGAIN loop above.
+ */
+ pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
+
+ return err;
+}
+
+static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+ struct task_struct *argowner)
+{
+ struct futex_pi_state *pi_state = q->pi_state;
+ int ret;
+
+ lockdep_assert_held(q->lock_ptr);
+
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+ ret = __fixup_pi_state_owner(uaddr, q, argowner);
+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+ return ret;
+}
+
+static long futex_wait_restart(struct restart_block *restart);
+
+/**
+ * fixup_owner() - Post lock pi_state and corner case management
+ * @uaddr: user address of the futex
+ * @q: futex_q (contains pi_state and access to the rt_mutex)
+ * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
+ *
+ * After attempting to lock an rt_mutex, this function is called to cleanup
+ * the pi_state owner as well as handle race conditions that may allow us to
+ * acquire the lock. Must be called with the hb lock held.
+ *
+ * Return:
+ * - 1 - success, lock taken;
+ * - 0 - success, lock not taken;
+ * - <0 - on error (-EFAULT)
+ */
+static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
+{
+ if (locked) {
+ /*
+ * Got the lock. We might not be the anticipated owner if we
+ * did a lock-steal - fix up the PI-state in that case:
+ *
+ * Speculative pi_state->owner read (we don't hold wait_lock);
+ * since we own the lock pi_state->owner == current is the
+ * stable state, anything else needs more attention.
+ */
+ if (q->pi_state->owner != current)
+ return fixup_pi_state_owner(uaddr, q, current);
+ return 1;
+ }
+
+ /*
+ * If we didn't get the lock; check if anybody stole it from us. In
+ * that case, we need to fix up the uval to point to them instead of
+ * us, otherwise bad things happen. [10]
+ *
+ * Another speculative read; pi_state->owner == current is unstable
+ * but needs our attention.
+ */
+ if (q->pi_state->owner == current)
+ return fixup_pi_state_owner(uaddr, q, NULL);
+
+ /*
+ * Paranoia check. If we did not take the lock, then we should not be
+ * the owner of the rt_mutex. Warn and establish consistent state.
+ */
+ if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
+ return fixup_pi_state_owner(uaddr, q, current);
+
+ return 0;
+}
+
+/**
+ * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
+ * @hb: the futex hash bucket, must be locked by the caller
+ * @q: the futex_q to queue up on
+ * @timeout: the prepared hrtimer_sleeper, or null for no timeout
+ */
+static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
+ struct hrtimer_sleeper *timeout)
+{
+ /*
+ * The task state is guaranteed to be set before another task can
+ * wake it. set_current_state() is implemented using smp_store_mb() and
+ * queue_me() calls spin_unlock() upon completion, both serializing
+ * access to the hash list and forcing another memory barrier.
+ */
+ set_current_state(TASK_INTERRUPTIBLE);
+ queue_me(q, hb);
+
+ /* Arm the timer */
+ if (timeout)
+ hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
+
+ /*
+ * If we have been removed from the hash list, then another task
+ * has tried to wake us, and we can skip the call to schedule().
+ */
+ if (likely(!plist_node_empty(&q->list))) {
+ /*
+ * If the timer has already expired, current will already be
+ * flagged for rescheduling. Only call schedule if there
+ * is no timeout, or if it has yet to expire.
+ */
+ if (!timeout || timeout->task)
+ freezable_schedule();
+ }
+ __set_current_state(TASK_RUNNING);
+}
+
+/**
+ * futex_wait_setup() - Prepare to wait on a futex
+ * @uaddr: the futex userspace address
+ * @val: the expected value
+ * @flags: futex flags (FLAGS_SHARED, etc.)
+ * @q: the associated futex_q
+ * @hb: storage for hash_bucket pointer to be returned to caller
+ *
+ * Setup the futex_q and locate the hash_bucket. Get the futex value and
+ * compare it with the expected value. Handle atomic faults internally.
+ * Return with the hb lock held on success, and unlocked on failure.
+ *
+ * Return:
+ * - 0 - uaddr contains val and hb has been locked;
+ * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
+ */
+static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
+ struct futex_q *q, struct futex_hash_bucket **hb)
+{
+ u32 uval;
+ int ret;
+
+ /*
+ * Access the page AFTER the hash-bucket is locked.
+ * Order is important:
+ *
+ * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
+ * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
+ *
+ * The basic logical guarantee of a futex is that it blocks ONLY
+ * if cond(var) is known to be true at the time of blocking, for
+ * any cond. If we locked the hash-bucket after testing *uaddr, that
+ * would open a race condition where we could block indefinitely with
+ * cond(var) false, which would violate the guarantee.
+ *
+ * On the other hand, we insert q and release the hash-bucket only
+ * after testing *uaddr. This guarantees that futex_wait() will NOT
+ * absorb a wakeup if *uaddr does not match the desired values
+ * while the syscall executes.
+ */
+retry:
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
+ if (unlikely(ret != 0))
+ return ret;
+
+retry_private:
+ *hb = queue_lock(q);
+
+ ret = get_futex_value_locked(&uval, uaddr);
+
+ if (ret) {
+ queue_unlock(*hb);
+
+ ret = get_user(uval, uaddr);
+ if (ret)
+ return ret;
+
+ if (!(flags & FLAGS_SHARED))
+ goto retry_private;
+
+ goto retry;
+ }
+
+ if (uval != val) {
+ queue_unlock(*hb);
+ ret = -EWOULDBLOCK;
+ }
+
+ return ret;
+}
+
+static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
+ ktime_t *abs_time, u32 bitset)
+{
+ struct hrtimer_sleeper timeout, *to;
+ struct restart_block *restart;
+ struct futex_hash_bucket *hb;
+ struct futex_q q = futex_q_init;
+ int ret;
+
+ if (!bitset)
+ return -EINVAL;
+ q.bitset = bitset;
+
+ to = futex_setup_timer(abs_time, &timeout, flags,
+ current->timer_slack_ns);
+retry:
+ /*
+ * Prepare to wait on uaddr. On success, it holds hb->lock and q
+ * is initialized.
+ */
+ ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
+ if (ret)
+ goto out;
+
+ /* queue_me and wait for wakeup, timeout, or a signal. */
+ futex_wait_queue_me(hb, &q, to);
+
+ /* If we were woken (and unqueued), we succeeded, whatever. */
+ ret = 0;
+ if (!unqueue_me(&q))
+ goto out;
+ ret = -ETIMEDOUT;
+ if (to && !to->task)
+ goto out;
+
+ /*
+ * We expect signal_pending(current), but we might be the
+ * victim of a spurious wakeup as well.
+ */
+ if (!signal_pending(current))
+ goto retry;
+
+ ret = -ERESTARTSYS;
+ if (!abs_time)
+ goto out;
+
+ restart = ¤t->restart_block;
+ restart->futex.uaddr = uaddr;
+ restart->futex.val = val;
+ restart->futex.time = *abs_time;
+ restart->futex.bitset = bitset;
+ restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
+
+ ret = set_restart_fn(restart, futex_wait_restart);
+
+out:
+ if (to) {
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+ }
+ return ret;
+}
+
+
+static long futex_wait_restart(struct restart_block *restart)
+{
+ u32 __user *uaddr = restart->futex.uaddr;
+ ktime_t t, *tp = NULL;
+
+ if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
+ t = restart->futex.time;
+ tp = &t;
+ }
+ restart->fn = do_no_restart_syscall;
+
+ return (long)futex_wait(uaddr, restart->futex.flags,
+ restart->futex.val, tp, restart->futex.bitset);
+}
+
+
+/*
+ * Userspace tried a 0 -> TID atomic transition of the futex value
+ * and failed. The kernel side here does the whole locking operation:
+ * if there are waiters then it will block as a consequence of relying
+ * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
+ * a 0 value of the futex too.).
+ *
+ * Also serves as futex trylock_pi()'ing, and due semantics.
+ */
+static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
+ ktime_t *time, int trylock)
+{
+ struct hrtimer_sleeper timeout, *to;
+ struct task_struct *exiting = NULL;
+ struct rt_mutex_waiter rt_waiter;
+ struct futex_hash_bucket *hb;
+ struct futex_q q = futex_q_init;
+ int res, ret;
+
+ if (!IS_ENABLED(CONFIG_FUTEX_PI))
+ return -ENOSYS;
+
+ if (refill_pi_state_cache())
+ return -ENOMEM;
+
+ to = futex_setup_timer(time, &timeout, flags, 0);
+
+retry:
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
+ if (unlikely(ret != 0))
+ goto out;
+
+retry_private:
+ hb = queue_lock(&q);
+
+ ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
+ &exiting, 0);
+ if (unlikely(ret)) {
+ /*
+ * Atomic work succeeded and we got the lock,
+ * or failed. Either way, we do _not_ block.
+ */
+ switch (ret) {
+ case 1:
+ /* We got the lock. */
+ ret = 0;
+ goto out_unlock_put_key;
+ case -EFAULT:
+ goto uaddr_faulted;
+ case -EBUSY:
+ case -EAGAIN:
+ /*
+ * Two reasons for this:
+ * - EBUSY: Task is exiting and we just wait for the
+ * exit to complete.
+ * - EAGAIN: The user space value changed.
+ */
+ queue_unlock(hb);
+ /*
+ * Handle the case where the owner is in the middle of
+ * exiting. Wait for the exit to complete otherwise
+ * this task might loop forever, aka. live lock.
+ */
+ wait_for_owner_exiting(ret, exiting);
+ cond_resched();
+ goto retry;
+ default:
+ goto out_unlock_put_key;
+ }
+ }
+
+ WARN_ON(!q.pi_state);
+
+ /*
+ * Only actually queue now that the atomic ops are done:
+ */
+ __queue_me(&q, hb);
+
+ if (trylock) {
+ ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
+ /* Fixup the trylock return value: */
+ ret = ret ? 0 : -EWOULDBLOCK;
+ goto no_block;
+ }
+
+ rt_mutex_init_waiter(&rt_waiter);
+
+ /*
+ * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
+ * hold it while doing rt_mutex_start_proxy(), because then it will
+ * include hb->lock in the blocking chain, even through we'll not in
+ * fact hold it while blocking. This will lead it to report -EDEADLK
+ * and BUG when futex_unlock_pi() interleaves with this.
+ *
+ * Therefore acquire wait_lock while holding hb->lock, but drop the
+ * latter before calling __rt_mutex_start_proxy_lock(). This
+ * interleaves with futex_unlock_pi() -- which does a similar lock
+ * handoff -- such that the latter can observe the futex_q::pi_state
+ * before __rt_mutex_start_proxy_lock() is done.
+ */
+ raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
+ spin_unlock(q.lock_ptr);
+ /*
+ * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
+ * such that futex_unlock_pi() is guaranteed to observe the waiter when
+ * it sees the futex_q::pi_state.
+ */
+ ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
+ raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
+
+ if (ret) {
+ if (ret == 1)
+ ret = 0;
+ goto cleanup;
+ }
+
+ if (unlikely(to))
+ hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
+
+ ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
+
+cleanup:
+ spin_lock(q.lock_ptr);
+ /*
+ * If we failed to acquire the lock (deadlock/signal/timeout), we must
+ * first acquire the hb->lock before removing the lock from the
+ * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
+ * lists consistent.
+ *
+ * In particular; it is important that futex_unlock_pi() can not
+ * observe this inconsistency.
+ */
+ if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
+ ret = 0;
+
+no_block:
+ /*
+ * Fixup the pi_state owner and possibly acquire the lock if we
+ * haven't already.
+ */
+ res = fixup_owner(uaddr, &q, !ret);
+ /*
+ * If fixup_owner() returned an error, propagate that. If it acquired
+ * the lock, clear our -ETIMEDOUT or -EINTR.
+ */
+ if (res)
+ ret = (res < 0) ? res : 0;
+
+ unqueue_me_pi(&q);
+ spin_unlock(q.lock_ptr);
+ goto out;
+
+out_unlock_put_key:
+ queue_unlock(hb);
+
+out:
+ if (to) {
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+ }
+ return ret != -EINTR ? ret : -ERESTARTNOINTR;
+
+uaddr_faulted:
+ queue_unlock(hb);
+
+ ret = fault_in_user_writeable(uaddr);
+ if (ret)
+ goto out;
+
+ if (!(flags & FLAGS_SHARED))
+ goto retry_private;
+
+ goto retry;
+}
+
+/*
+ * Userspace attempted a TID -> 0 atomic transition, and failed.
+ * This is the in-kernel slowpath: we look up the PI state (if any),
+ * and do the rt-mutex unlock.
+ */
+static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+{
+ u32 curval, uval, vpid = task_pid_vnr(current);
+ union futex_key key = FUTEX_KEY_INIT;
+ struct futex_hash_bucket *hb;
+ struct futex_q *top_waiter;
+ int ret;
+
+ if (!IS_ENABLED(CONFIG_FUTEX_PI))
+ return -ENOSYS;
+
+retry:
+ if (get_user(uval, uaddr))
+ return -EFAULT;
+ /*
+ * We release only a lock we actually own:
+ */
+ if ((uval & FUTEX_TID_MASK) != vpid)
+ return -EPERM;
+
+ ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
+ if (ret)
+ return ret;
+
+ hb = hash_futex(&key);
+ spin_lock(&hb->lock);
+
+ /*
+ * Check waiters first. We do not trust user space values at
+ * all and we at least want to know if user space fiddled
+ * with the futex value instead of blindly unlocking.
+ */
+ top_waiter = futex_top_waiter(hb, &key);
+ if (top_waiter) {
+ struct futex_pi_state *pi_state = top_waiter->pi_state;
+
+ ret = -EINVAL;
+ if (!pi_state)
+ goto out_unlock;
+
+ /*
+ * If current does not own the pi_state then the futex is
+ * inconsistent and user space fiddled with the futex value.
+ */
+ if (pi_state->owner != current)
+ goto out_unlock;
+
+ get_pi_state(pi_state);
+ /*
+ * By taking wait_lock while still holding hb->lock, we ensure
+ * there is no point where we hold neither; and therefore
+ * wake_futex_pi() must observe a state consistent with what we
+ * observed.
+ *
+ * In particular; this forces __rt_mutex_start_proxy() to
+ * complete such that we're guaranteed to observe the
+ * rt_waiter. Also see the WARN in wake_futex_pi().
+ */
+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+ spin_unlock(&hb->lock);
+
+ /* drops pi_state->pi_mutex.wait_lock */
+ ret = wake_futex_pi(uaddr, uval, pi_state);
+
+ put_pi_state(pi_state);
+
+ /*
+ * Success, we're done! No tricky corner cases.
+ */
+ if (!ret)
+ return ret;
+ /*
+ * The atomic access to the futex value generated a
+ * pagefault, so retry the user-access and the wakeup:
+ */
+ if (ret == -EFAULT)
+ goto pi_faulted;
+ /*
+ * A unconditional UNLOCK_PI op raced against a waiter
+ * setting the FUTEX_WAITERS bit. Try again.
+ */
+ if (ret == -EAGAIN)
+ goto pi_retry;
+ /*
+ * wake_futex_pi has detected invalid state. Tell user
+ * space.
+ */
+ return ret;
+ }
+
+ /*
+ * We have no kernel internal state, i.e. no waiters in the
+ * kernel. Waiters which are about to queue themselves are stuck
+ * on hb->lock. So we can safely ignore them. We do neither
+ * preserve the WAITERS bit not the OWNER_DIED one. We are the
+ * owner.
+ */
+ if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
+ spin_unlock(&hb->lock);
+ switch (ret) {
+ case -EFAULT:
+ goto pi_faulted;
+
+ case -EAGAIN:
+ goto pi_retry;
+
+ default:
+ WARN_ON_ONCE(1);
+ return ret;
+ }
+ }
+
+ /*
+ * If uval has changed, let user space handle it.
+ */
+ ret = (curval == uval) ? 0 : -EAGAIN;
+
+out_unlock:
+ spin_unlock(&hb->lock);
+ return ret;
+
+pi_retry:
+ cond_resched();
+ goto retry;
+
+pi_faulted:
+
+ ret = fault_in_user_writeable(uaddr);
+ if (!ret)
+ goto retry;
+
+ return ret;
+}
+
+/**
+ * handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
+ * @hb: the hash_bucket futex_q was original enqueued on
+ * @q: the futex_q woken while waiting to be requeued
+ * @timeout: the timeout associated with the wait (NULL if none)
+ *
+ * Determine the cause for the early wakeup.
+ *
+ * Return:
+ * -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR
+ */
+static inline
+int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
+ struct futex_q *q,
+ struct hrtimer_sleeper *timeout)
+{
+ int ret;
+
+ /*
+ * With the hb lock held, we avoid races while we process the wakeup.
+ * We only need to hold hb (and not hb2) to ensure atomicity as the
+ * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
+ * It can't be requeued from uaddr2 to something else since we don't
+ * support a PI aware source futex for requeue.
+ */
+ WARN_ON_ONCE(&hb->lock != q->lock_ptr);
+
+ /*
+ * We were woken prior to requeue by a timeout or a signal.
+ * Unqueue the futex_q and determine which it was.
+ */
+ plist_del(&q->list, &hb->chain);
+ hb_waiters_dec(hb);
+
+ /* Handle spurious wakeups gracefully */
+ ret = -EWOULDBLOCK;
+ if (timeout && !timeout->task)
+ ret = -ETIMEDOUT;
+ else if (signal_pending(current))
+ ret = -ERESTARTNOINTR;
+ return ret;
+}
+
+/**
+ * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
+ * @uaddr: the futex we initially wait on (non-pi)
+ * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
+ * the same type, no requeueing from private to shared, etc.
+ * @val: the expected value of uaddr
+ * @abs_time: absolute timeout
+ * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
+ * @uaddr2: the pi futex we will take prior to returning to user-space
+ *
+ * The caller will wait on uaddr and will be requeued by futex_requeue() to
+ * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
+ * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
+ * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
+ * without one, the pi logic would not know which task to boost/deboost, if
+ * there was a need to.
+ *
+ * We call schedule in futex_wait_queue_me() when we enqueue and return there
+ * via the following--
+ * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
+ * 2) wakeup on uaddr2 after a requeue
+ * 3) signal
+ * 4) timeout
+ *
+ * If 3, cleanup and return -ERESTARTNOINTR.
+ *
+ * If 2, we may then block on trying to take the rt_mutex and return via:
+ * 5) successful lock
+ * 6) signal
+ * 7) timeout
+ * 8) other lock acquisition failure
+ *
+ * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
+ *
+ * If 4 or 7, we cleanup and return with -ETIMEDOUT.
+ *
+ * Return:
+ * - 0 - On success;
+ * - <0 - On error
+ */
+static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+ u32 val, ktime_t *abs_time, u32 bitset,
+ u32 __user *uaddr2)
+{
+ struct hrtimer_sleeper timeout, *to;
+ struct rt_mutex_waiter rt_waiter;
+ struct futex_hash_bucket *hb;
+ union futex_key key2 = FUTEX_KEY_INIT;
+ struct futex_q q = futex_q_init;
+ struct rt_mutex_base *pi_mutex;
+ int res, ret;
+
+ if (!IS_ENABLED(CONFIG_FUTEX_PI))
+ return -ENOSYS;
+
+ if (uaddr == uaddr2)
+ return -EINVAL;
+
+ if (!bitset)
+ return -EINVAL;
+
+ to = futex_setup_timer(abs_time, &timeout, flags,
+ current->timer_slack_ns);
+
+ /*
+ * The waiter is allocated on our stack, manipulated by the requeue
+ * code while we sleep on uaddr.
+ */
+ rt_mutex_init_waiter(&rt_waiter);
+
+ ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
+ if (unlikely(ret != 0))
+ goto out;
+
+ q.bitset = bitset;
+ q.rt_waiter = &rt_waiter;
+ q.requeue_pi_key = &key2;
+
+ /*
+ * Prepare to wait on uaddr. On success, it holds hb->lock and q
+ * is initialized.
+ */
+ ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
+ if (ret)
+ goto out;
+
+ /*
+ * The check above which compares uaddrs is not sufficient for
+ * shared futexes. We need to compare the keys:
+ */
+ if (match_futex(&q.key, &key2)) {
+ queue_unlock(hb);
+ ret = -EINVAL;
+ goto out;
+ }
+
+ /* Queue the futex_q, drop the hb lock, wait for wakeup. */
+ futex_wait_queue_me(hb, &q, to);
+
+ switch (futex_requeue_pi_wakeup_sync(&q)) {
+ case Q_REQUEUE_PI_IGNORE:
+ /* The waiter is still on uaddr1 */
+ spin_lock(&hb->lock);
+ ret = handle_early_requeue_pi_wakeup(hb, &q, to);
+ spin_unlock(&hb->lock);
+ break;
+
+ case Q_REQUEUE_PI_LOCKED:
+ /* The requeue acquired the lock */
+ if (q.pi_state && (q.pi_state->owner != current)) {
+ spin_lock(q.lock_ptr);
+ ret = fixup_owner(uaddr2, &q, true);
+ /*
+ * Drop the reference to the pi state which the
+ * requeue_pi() code acquired for us.
+ */
+ put_pi_state(q.pi_state);
+ spin_unlock(q.lock_ptr);
+ /*
+ * Adjust the return value. It's either -EFAULT or
+ * success (1) but the caller expects 0 for success.
+ */
+ ret = ret < 0 ? ret : 0;
+ }
+ break;
+
+ case Q_REQUEUE_PI_DONE:
+ /* Requeue completed. Current is 'pi_blocked_on' the rtmutex */
+ pi_mutex = &q.pi_state->pi_mutex;
+ ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
+
+ /* Current is not longer pi_blocked_on */
+ spin_lock(q.lock_ptr);
+ if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
+ ret = 0;
+
+ debug_rt_mutex_free_waiter(&rt_waiter);
+ /*
+ * Fixup the pi_state owner and possibly acquire the lock if we
+ * haven't already.
+ */
+ res = fixup_owner(uaddr2, &q, !ret);
+ /*
+ * If fixup_owner() returned an error, propagate that. If it
+ * acquired the lock, clear -ETIMEDOUT or -EINTR.
+ */
+ if (res)
+ ret = (res < 0) ? res : 0;
+
+ unqueue_me_pi(&q);
+ spin_unlock(q.lock_ptr);
+
+ if (ret == -EINTR) {
+ /*
+ * We've already been requeued, but cannot restart
+ * by calling futex_lock_pi() directly. We could
+ * restart this syscall, but it would detect that
+ * the user space "val" changed and return
+ * -EWOULDBLOCK. Save the overhead of the restart
+ * and return -EWOULDBLOCK directly.
+ */
+ ret = -EWOULDBLOCK;
+ }
+ break;
+ default:
+ BUG();
+ }
+
+out:
+ if (to) {
+ hrtimer_cancel(&to->timer);
+ destroy_hrtimer_on_stack(&to->timer);
+ }
+ return ret;
+}
+
+/*
+ * Support for robust futexes: the kernel cleans up held futexes at
+ * thread exit time.
+ *
+ * Implementation: user-space maintains a per-thread list of locks it
+ * is holding. Upon do_exit(), the kernel carefully walks this list,
+ * and marks all locks that are owned by this thread with the
+ * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
+ * always manipulated with the lock held, so the list is private and
+ * per-thread. Userspace also maintains a per-thread 'list_op_pending'
+ * field, to allow the kernel to clean up if the thread dies after
+ * acquiring the lock, but just before it could have added itself to
+ * the list. There can only be one such pending lock.
+ */
+
+/**
+ * sys_set_robust_list() - Set the robust-futex list head of a task
+ * @head: pointer to the list-head
+ * @len: length of the list-head, as userspace expects
+ */
+SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
+ size_t, len)
+{
+ if (!futex_cmpxchg_enabled)
+ return -ENOSYS;
+ /*
+ * The kernel knows only one size for now:
+ */
+ if (unlikely(len != sizeof(*head)))
+ return -EINVAL;
+
+ current->robust_list = head;
+
+ return 0;
+}
+
+/**
+ * sys_get_robust_list() - Get the robust-futex list head of a task
+ * @pid: pid of the process [zero for current task]
+ * @head_ptr: pointer to a list-head pointer, the kernel fills it in
+ * @len_ptr: pointer to a length field, the kernel fills in the header size
+ */
+SYSCALL_DEFINE3(get_robust_list, int, pid,
+ struct robust_list_head __user * __user *, head_ptr,
+ size_t __user *, len_ptr)
+{
+ struct robust_list_head __user *head;
+ unsigned long ret;
+ struct task_struct *p;
+
+ if (!futex_cmpxchg_enabled)
+ return -ENOSYS;
+
+ rcu_read_lock();
+
+ ret = -ESRCH;
+ if (!pid)
+ p = current;
+ else {
+ p = find_task_by_vpid(pid);
+ if (!p)
+ goto err_unlock;
+ }
+
+ ret = -EPERM;
+ if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
+ goto err_unlock;
+
+ head = p->robust_list;
+ rcu_read_unlock();
+
+ if (put_user(sizeof(*head), len_ptr))
+ return -EFAULT;
+ return put_user(head, head_ptr);
+
+err_unlock:
+ rcu_read_unlock();
+
+ return ret;
+}
+
+/* Constants for the pending_op argument of handle_futex_death */
+#define HANDLE_DEATH_PENDING true
+#define HANDLE_DEATH_LIST false
+
+/*
+ * Process a futex-list entry, check whether it's owned by the
+ * dying task, and do notification if so:
+ */
+static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
+ bool pi, bool pending_op)
+{
+ u32 uval, nval, mval;
+ int err;
+
+ /* Futex address must be 32bit aligned */
+ if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
+ return -1;
+
+retry:
+ if (get_user(uval, uaddr))
+ return -1;
+
+ /*
+ * Special case for regular (non PI) futexes. The unlock path in
+ * user space has two race scenarios:
+ *
+ * 1. The unlock path releases the user space futex value and
+ * before it can execute the futex() syscall to wake up
+ * waiters it is killed.
+ *
+ * 2. A woken up waiter is killed before it can acquire the
+ * futex in user space.
+ *
+ * In both cases the TID validation below prevents a wakeup of
+ * potential waiters which can cause these waiters to block
+ * forever.
+ *
+ * In both cases the following conditions are met:
+ *
+ * 1) task->robust_list->list_op_pending != NULL
+ * @pending_op == true
+ * 2) User space futex value == 0
+ * 3) Regular futex: @pi == false
+ *
+ * If these conditions are met, it is safe to attempt waking up a
+ * potential waiter without touching the user space futex value and
+ * trying to set the OWNER_DIED bit. The user space futex value is
+ * uncontended and the rest of the user space mutex state is
+ * consistent, so a woken waiter will just take over the
+ * uncontended futex. Setting the OWNER_DIED bit would create
+ * inconsistent state and malfunction of the user space owner died
+ * handling.
+ */
+ if (pending_op && !pi && !uval) {
+ futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+ return 0;
+ }
+
+ if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
+ return 0;
+
+ /*
+ * Ok, this dying thread is truly holding a futex
+ * of interest. Set the OWNER_DIED bit atomically
+ * via cmpxchg, and if the value had FUTEX_WAITERS
+ * set, wake up a waiter (if any). (We have to do a
+ * futex_wake() even if OWNER_DIED is already set -
+ * to handle the rare but possible case of recursive
+ * thread-death.) The rest of the cleanup is done in
+ * userspace.
+ */
+ mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
+
+ /*
+ * We are not holding a lock here, but we want to have
+ * the pagefault_disable/enable() protection because
+ * we want to handle the fault gracefully. If the
+ * access fails we try to fault in the futex with R/W
+ * verification via get_user_pages. get_user() above
+ * does not guarantee R/W access. If that fails we
+ * give up and leave the futex locked.
+ */
+ if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
+ switch (err) {
+ case -EFAULT:
+ if (fault_in_user_writeable(uaddr))
+ return -1;
+ goto retry;
+
+ case -EAGAIN:
+ cond_resched();
+ goto retry;
+
+ default:
+ WARN_ON_ONCE(1);
+ return err;
+ }
+ }
+
+ if (nval != uval)
+ goto retry;
+
+ /*
+ * Wake robust non-PI futexes here. The wakeup of
+ * PI futexes happens in exit_pi_state():
+ */
+ if (!pi && (uval & FUTEX_WAITERS))
+ futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+
+ return 0;
+}
+
+/*
+ * Fetch a robust-list pointer. Bit 0 signals PI futexes:
+ */
+static inline int fetch_robust_entry(struct robust_list __user **entry,
+ struct robust_list __user * __user *head,
+ unsigned int *pi)
+{
+ unsigned long uentry;
+
+ if (get_user(uentry, (unsigned long __user *)head))
+ return -EFAULT;
+
+ *entry = (void __user *)(uentry & ~1UL);
+ *pi = uentry & 1;
+
+ return 0;
+}
+
+/*
+ * Walk curr->robust_list (very carefully, it's a userspace list!)
+ * and mark any locks found there dead, and notify any waiters.
+ *
+ * We silently return on any sign of list-walking problem.
+ */
+static void exit_robust_list(struct task_struct *curr)
+{
+ struct robust_list_head __user *head = curr->robust_list;
+ struct robust_list __user *entry, *next_entry, *pending;
+ unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
+ unsigned int next_pi;
+ unsigned long futex_offset;
+ int rc;
+
+ if (!futex_cmpxchg_enabled)
+ return;
+
+ /*
+ * Fetch the list head (which was registered earlier, via
+ * sys_set_robust_list()):
+ */
+ if (fetch_robust_entry(&entry, &head->list.next, &pi))
+ return;
+ /*
+ * Fetch the relative futex offset:
+ */
+ if (get_user(futex_offset, &head->futex_offset))
+ return;
+ /*
+ * Fetch any possibly pending lock-add first, and handle it
+ * if it exists:
+ */
+ if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
+ return;
+
+ next_entry = NULL; /* avoid warning with gcc */
+ while (entry != &head->list) {
+ /*
+ * Fetch the next entry in the list before calling
+ * handle_futex_death:
+ */
+ rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
+ /*
+ * A pending lock might already be on the list, so
+ * don't process it twice:
+ */
+ if (entry != pending) {
+ if (handle_futex_death((void __user *)entry + futex_offset,
+ curr, pi, HANDLE_DEATH_LIST))
+ return;
+ }
+ if (rc)
+ return;
+ entry = next_entry;
+ pi = next_pi;
+ /*
+ * Avoid excessively long or circular lists:
+ */
+ if (!--limit)
+ break;
+
+ cond_resched();
+ }
+
+ if (pending) {
+ handle_futex_death((void __user *)pending + futex_offset,
+ curr, pip, HANDLE_DEATH_PENDING);
+ }
+}
+
+static void futex_cleanup(struct task_struct *tsk)
+{
+ if (unlikely(tsk->robust_list)) {
+ exit_robust_list(tsk);
+ tsk->robust_list = NULL;
+ }
+
+#ifdef CONFIG_COMPAT
+ if (unlikely(tsk->compat_robust_list)) {
+ compat_exit_robust_list(tsk);
+ tsk->compat_robust_list = NULL;
+ }
+#endif
+
+ if (unlikely(!list_empty(&tsk->pi_state_list)))
+ exit_pi_state_list(tsk);
+}
+
+/**
+ * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
+ * @tsk: task to set the state on
+ *
+ * Set the futex exit state of the task lockless. The futex waiter code
+ * observes that state when a task is exiting and loops until the task has
+ * actually finished the futex cleanup. The worst case for this is that the
+ * waiter runs through the wait loop until the state becomes visible.
+ *
+ * This is called from the recursive fault handling path in do_exit().
+ *
+ * This is best effort. Either the futex exit code has run already or
+ * not. If the OWNER_DIED bit has been set on the futex then the waiter can
+ * take it over. If not, the problem is pushed back to user space. If the
+ * futex exit code did not run yet, then an already queued waiter might
+ * block forever, but there is nothing which can be done about that.
+ */
+void futex_exit_recursive(struct task_struct *tsk)
+{
+ /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
+ if (tsk->futex_state == FUTEX_STATE_EXITING)
+ mutex_unlock(&tsk->futex_exit_mutex);
+ tsk->futex_state = FUTEX_STATE_DEAD;
+}
+
+static void futex_cleanup_begin(struct task_struct *tsk)
+{
+ /*
+ * Prevent various race issues against a concurrent incoming waiter
+ * including live locks by forcing the waiter to block on
+ * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
+ * attach_to_pi_owner().
+ */
+ mutex_lock(&tsk->futex_exit_mutex);
+
+ /*
+ * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
+ *
+ * This ensures that all subsequent checks of tsk->futex_state in
+ * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
+ * tsk->pi_lock held.
+ *
+ * It guarantees also that a pi_state which was queued right before
+ * the state change under tsk->pi_lock by a concurrent waiter must
+ * be observed in exit_pi_state_list().
+ */
+ raw_spin_lock_irq(&tsk->pi_lock);
+ tsk->futex_state = FUTEX_STATE_EXITING;
+ raw_spin_unlock_irq(&tsk->pi_lock);
+}
+
+static void futex_cleanup_end(struct task_struct *tsk, int state)
+{
+ /*
+ * Lockless store. The only side effect is that an observer might
+ * take another loop until it becomes visible.
+ */
+ tsk->futex_state = state;
+ /*
+ * Drop the exit protection. This unblocks waiters which observed
+ * FUTEX_STATE_EXITING to reevaluate the state.
+ */
+ mutex_unlock(&tsk->futex_exit_mutex);
+}
+
+void futex_exec_release(struct task_struct *tsk)
+{
+ /*
+ * The state handling is done for consistency, but in the case of
+ * exec() there is no way to prevent further damage as the PID stays
+ * the same. But for the unlikely and arguably buggy case that a
+ * futex is held on exec(), this provides at least as much state
+ * consistency protection which is possible.
+ */
+ futex_cleanup_begin(tsk);
+ futex_cleanup(tsk);
+ /*
+ * Reset the state to FUTEX_STATE_OK. The task is alive and about
+ * exec a new binary.
+ */
+ futex_cleanup_end(tsk, FUTEX_STATE_OK);
+}
+
+void futex_exit_release(struct task_struct *tsk)
+{
+ futex_cleanup_begin(tsk);
+ futex_cleanup(tsk);
+ futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
+}
+
+long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
+ u32 __user *uaddr2, u32 val2, u32 val3)
+{
+ int cmd = op & FUTEX_CMD_MASK;
+ unsigned int flags = 0;
+
+ if (!(op & FUTEX_PRIVATE_FLAG))
+ flags |= FLAGS_SHARED;
+
+ if (op & FUTEX_CLOCK_REALTIME) {
+ flags |= FLAGS_CLOCKRT;
+ if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
+ cmd != FUTEX_LOCK_PI2)
+ return -ENOSYS;
+ }
+
+ switch (cmd) {
+ case FUTEX_LOCK_PI:
+ case FUTEX_LOCK_PI2:
+ case FUTEX_UNLOCK_PI:
+ case FUTEX_TRYLOCK_PI:
+ case FUTEX_WAIT_REQUEUE_PI:
+ case FUTEX_CMP_REQUEUE_PI:
+ if (!futex_cmpxchg_enabled)
+ return -ENOSYS;
+ }
+
+ switch (cmd) {
+ case FUTEX_WAIT:
+ val3 = FUTEX_BITSET_MATCH_ANY;
+ fallthrough;
+ case FUTEX_WAIT_BITSET:
+ return futex_wait(uaddr, flags, val, timeout, val3);
+ case FUTEX_WAKE:
+ val3 = FUTEX_BITSET_MATCH_ANY;
+ fallthrough;
+ case FUTEX_WAKE_BITSET:
+ return futex_wake(uaddr, flags, val, val3);
+ case FUTEX_REQUEUE:
+ return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
+ case FUTEX_CMP_REQUEUE:
+ return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
+ case FUTEX_WAKE_OP:
+ return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
+ case FUTEX_LOCK_PI:
+ flags |= FLAGS_CLOCKRT;
+ fallthrough;
+ case FUTEX_LOCK_PI2:
+ return futex_lock_pi(uaddr, flags, timeout, 0);
+ case FUTEX_UNLOCK_PI:
+ return futex_unlock_pi(uaddr, flags);
+ case FUTEX_TRYLOCK_PI:
+ return futex_lock_pi(uaddr, flags, NULL, 1);
+ case FUTEX_WAIT_REQUEUE_PI:
+ val3 = FUTEX_BITSET_MATCH_ANY;
+ return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
+ uaddr2);
+ case FUTEX_CMP_REQUEUE_PI:
+ return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
+ }
+ return -ENOSYS;
+}
+
+static __always_inline bool futex_cmd_has_timeout(u32 cmd)
+{
+ switch (cmd) {
+ case FUTEX_WAIT:
+ case FUTEX_LOCK_PI:
+ case FUTEX_LOCK_PI2:
+ case FUTEX_WAIT_BITSET:
+ case FUTEX_WAIT_REQUEUE_PI:
+ return true;
+ }
+ return false;
+}
+
+static __always_inline int
+futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
+{
+ if (!timespec64_valid(ts))
+ return -EINVAL;
+
+ *t = timespec64_to_ktime(*ts);
+ if (cmd == FUTEX_WAIT)
+ *t = ktime_add_safe(ktime_get(), *t);
+ else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
+ *t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
+ return 0;
+}
+
+SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
+ const struct __kernel_timespec __user *, utime,
+ u32 __user *, uaddr2, u32, val3)
+{
+ int ret, cmd = op & FUTEX_CMD_MASK;
+ ktime_t t, *tp = NULL;
+ struct timespec64 ts;
+
+ if (utime && futex_cmd_has_timeout(cmd)) {
+ if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
+ return -EFAULT;
+ if (get_timespec64(&ts, utime))
+ return -EFAULT;
+ ret = futex_init_timeout(cmd, op, &ts, &t);
+ if (ret)
+ return ret;
+ tp = &t;
+ }
+
+ return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+}
+
+#ifdef CONFIG_COMPAT
+/*
+ * Fetch a robust-list pointer. Bit 0 signals PI futexes:
+ */
+static inline int
+compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
+ compat_uptr_t __user *head, unsigned int *pi)
+{
+ if (get_user(*uentry, head))
+ return -EFAULT;
+
+ *entry = compat_ptr((*uentry) & ~1);
+ *pi = (unsigned int)(*uentry) & 1;
+
+ return 0;
+}
+
+static void __user *futex_uaddr(struct robust_list __user *entry,
+ compat_long_t futex_offset)
+{
+ compat_uptr_t base = ptr_to_compat(entry);
+ void __user *uaddr = compat_ptr(base + futex_offset);
+
+ return uaddr;
+}
+
+/*
+ * Walk curr->robust_list (very carefully, it's a userspace list!)
+ * and mark any locks found there dead, and notify any waiters.
+ *
+ * We silently return on any sign of list-walking problem.
+ */
+static void compat_exit_robust_list(struct task_struct *curr)
+{
+ struct compat_robust_list_head __user *head = curr->compat_robust_list;
+ struct robust_list __user *entry, *next_entry, *pending;
+ unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
+ unsigned int next_pi;
+ compat_uptr_t uentry, next_uentry, upending;
+ compat_long_t futex_offset;
+ int rc;
+
+ if (!futex_cmpxchg_enabled)
+ return;
+
+ /*
+ * Fetch the list head (which was registered earlier, via
+ * sys_set_robust_list()):
+ */
+ if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
+ return;
+ /*
+ * Fetch the relative futex offset:
+ */
+ if (get_user(futex_offset, &head->futex_offset))
+ return;
+ /*
+ * Fetch any possibly pending lock-add first, and handle it
+ * if it exists:
+ */
+ if (compat_fetch_robust_entry(&upending, &pending,
+ &head->list_op_pending, &pip))
+ return;
+
+ next_entry = NULL; /* avoid warning with gcc */
+ while (entry != (struct robust_list __user *) &head->list) {
+ /*
+ * Fetch the next entry in the list before calling
+ * handle_futex_death:
+ */
+ rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
+ (compat_uptr_t __user *)&entry->next, &next_pi);
+ /*
+ * A pending lock might already be on the list, so
+ * dont process it twice:
+ */
+ if (entry != pending) {
+ void __user *uaddr = futex_uaddr(entry, futex_offset);
+
+ if (handle_futex_death(uaddr, curr, pi,
+ HANDLE_DEATH_LIST))
+ return;
+ }
+ if (rc)
+ return;
+ uentry = next_uentry;
+ entry = next_entry;
+ pi = next_pi;
+ /*
+ * Avoid excessively long or circular lists:
+ */
+ if (!--limit)
+ break;
+
+ cond_resched();
+ }
+ if (pending) {
+ void __user *uaddr = futex_uaddr(pending, futex_offset);
+
+ handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
+ }
+}
+
+COMPAT_SYSCALL_DEFINE2(set_robust_list,
+ struct compat_robust_list_head __user *, head,
+ compat_size_t, len)
+{
+ if (!futex_cmpxchg_enabled)
+ return -ENOSYS;
+
+ if (unlikely(len != sizeof(*head)))
+ return -EINVAL;
+
+ current->compat_robust_list = head;
+
+ return 0;
+}
+
+COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
+ compat_uptr_t __user *, head_ptr,
+ compat_size_t __user *, len_ptr)
+{
+ struct compat_robust_list_head __user *head;
+ unsigned long ret;
+ struct task_struct *p;
+
+ if (!futex_cmpxchg_enabled)
+ return -ENOSYS;
+
+ rcu_read_lock();
+
+ ret = -ESRCH;
+ if (!pid)
+ p = current;
+ else {
+ p = find_task_by_vpid(pid);
+ if (!p)
+ goto err_unlock;
+ }
+
+ ret = -EPERM;
+ if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
+ goto err_unlock;
+
+ head = p->compat_robust_list;
+ rcu_read_unlock();
+
+ if (put_user(sizeof(*head), len_ptr))
+ return -EFAULT;
+ return put_user(ptr_to_compat(head), head_ptr);
+
+err_unlock:
+ rcu_read_unlock();
+
+ return ret;
+}
+#endif /* CONFIG_COMPAT */
+
+#ifdef CONFIG_COMPAT_32BIT_TIME
+SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
+ const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
+ u32, val3)
+{
+ int ret, cmd = op & FUTEX_CMD_MASK;
+ ktime_t t, *tp = NULL;
+ struct timespec64 ts;
+
+ if (utime && futex_cmd_has_timeout(cmd)) {
+ if (get_old_timespec32(&ts, utime))
+ return -EFAULT;
+ ret = futex_init_timeout(cmd, op, &ts, &t);
+ if (ret)
+ return ret;
+ tp = &t;
+ }
+
+ return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+}
+#endif /* CONFIG_COMPAT_32BIT_TIME */
+
+static void __init futex_detect_cmpxchg(void)
+{
+#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
+ u32 curval;
+
+ /*
+ * This will fail and we want it. Some arch implementations do
+ * runtime detection of the futex_atomic_cmpxchg_inatomic()
+ * functionality. We want to know that before we call in any
+ * of the complex code paths. Also we want to prevent
+ * registration of robust lists in that case. NULL is
+ * guaranteed to fault and we get -EFAULT on functional
+ * implementation, the non-functional ones will return
+ * -ENOSYS.
+ */
+ if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
+ futex_cmpxchg_enabled = 1;
+#endif
+}
+
+static int __init futex_init(void)
+{
+ unsigned int futex_shift;
+ unsigned long i;
+
+#if CONFIG_BASE_SMALL
+ futex_hashsize = 16;
+#else
+ futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
+#endif
+
+ futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
+ futex_hashsize, 0,
+ futex_hashsize < 256 ? HASH_SMALL : 0,
+ &futex_shift, NULL,
+ futex_hashsize, futex_hashsize);
+ futex_hashsize = 1UL << futex_shift;
+
+ futex_detect_cmpxchg();
+
+ for (i = 0; i < futex_hashsize; i++) {
+ atomic_set(&futex_queues[i].waiters, 0);
+ plist_head_init(&futex_queues[i].chain);
+ spin_lock_init(&futex_queues[i].lock);
+ }
+
+ return 0;
+}
+core_initcall(futex_init);
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