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Message-ID: <20210915141525.425686609@infradead.org>
Date: Wed, 15 Sep 2021 16:07:23 +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 13/20] futex: Split out requeue
Move all the requeue bits into their own file.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
kernel/futex/Makefile | 2
kernel/futex/core.c | 966 -------------------------------------------------
kernel/futex/futex.h | 77 +++
kernel/futex/requeue.c | 897 +++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 979 insertions(+), 963 deletions(-)
--- a/kernel/futex/Makefile
+++ b/kernel/futex/Makefile
@@ -1,3 +1,3 @@
# SPDX-License-Identifier: GPL-2.0
-obj-y += core.o syscalls.o pi.o
+obj-y += core.o syscalls.o pi.o requeue.o
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -148,64 +148,6 @@ int __read_mostly futex_cmpxchg_enabled
/*
- * 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,
-};
-
-const struct futex_q futex_q_init = {
- /* list gets initialized in futex_queue()*/
- .key = FUTEX_KEY_INIT,
- .bitset = FUTEX_BITSET_MATCH_ANY,
- .requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE),
-};
-
-/*
* The base of the bucket array and its size are always used together
* (after initialization only in futex_hash()), so ensure that they
* reside in the same cacheline.
@@ -269,31 +211,6 @@ late_initcall(fail_futex_debugfs);
#endif /* CONFIG_FAIL_FUTEX */
-/*
- * Reflects a new waiter being added to the waitqueue.
- */
-static inline void futex_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 futex_hb_waiters_dec(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
- atomic_dec(&hb->waiters);
-#endif
-}
-
static inline int futex_hb_waiters_pending(struct futex_hash_bucket *hb)
{
#ifdef CONFIG_SMP
@@ -324,21 +241,6 @@ struct futex_hash_bucket *futex_hash(uni
/**
- * futex_match - 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 futex_match(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);
-}
-
-/**
* futex_setup_timer - set up the sleeping hrtimer.
* @time: ptr to the given timeout value
* @timeout: the hrtimer_sleeper structure to be set up
@@ -713,7 +615,7 @@ void wait_for_owner_exiting(int ret, str
*
* The q->lock_ptr must not be NULL and must be held by the caller.
*/
-static void __futex_unqueue(struct futex_q *q)
+void __futex_unqueue(struct futex_q *q)
{
struct futex_hash_bucket *hb;
@@ -732,7 +634,7 @@ static void __futex_unqueue(struct futex
* must ensure to later call wake_up_q() for the actual
* wakeups to occur.
*/
-static void futex_wake_mark(struct wake_q_head *wake_q, struct futex_q *q)
+void futex_wake_mark(struct wake_q_head *wake_q, struct futex_q *q)
{
struct task_struct *p = q->task;
@@ -758,30 +660,6 @@ static void futex_wake_mark(struct wake_
}
/*
- * 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).
*/
int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
@@ -961,619 +839,6 @@ int futex_wake_op(u32 __user *uaddr1, un
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);
- futex_hb_waiters_dec(hb1);
- futex_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;
-
- __futex_unqueue(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 (futex_get_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 (!futex_match(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
- */
-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 && futex_match(&key1, &key2))
- return -EINVAL;
-
- hb1 = futex_hash(&key1);
- hb2 = futex_hash(&key2);
-
-retry_private:
- futex_hb_waiters_inc(hb2);
- double_lock_hb(hb1, hb2);
-
- if (likely(cmpval != NULL)) {
- u32 curval;
-
- ret = futex_get_value_locked(&curval, uaddr1);
-
- if (unlikely(ret)) {
- double_unlock_hb(hb1, hb2);
- futex_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);
- futex_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);
- futex_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 (!futex_match(&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)
- futex_wake_mark(&wake_q, this);
- else
- requeue_futex(this, hb1, hb2, &key2);
- continue;
- }
-
- /* Ensure we requeue to the expected futex for requeue_pi. */
- if (!futex_match(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);
- futex_hb_waiters_dec(hb2);
- return ret ? ret : task_count;
-}
-
/* The key must be already stored in q->key. */
struct futex_hash_bucket *futex_q_lock(struct futex_q *q)
__acquires(&hb->lock)
@@ -1718,8 +983,8 @@ static long futex_wait_restart(struct re
* @q: the futex_q to queue up on
* @timeout: the prepared hrtimer_sleeper, or null for no timeout
*/
-static void futex_wait_queue(struct futex_hash_bucket *hb, struct futex_q *q,
- struct hrtimer_sleeper *timeout)
+void futex_wait_queue(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
@@ -1766,8 +1031,8 @@ static void futex_wait_queue(struct fute
* - 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)
+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;
@@ -1900,225 +1165,6 @@ static long futex_wait_restart(struct re
}
-/**
- * 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);
- futex_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() 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
- */
-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 (futex_match(&q.key, &key2)) {
- futex_q_unlock(hb);
- ret = -EINVAL;
- goto out;
- }
-
- /* Queue the futex_q, drop the hb lock, wait for wakeup. */
- futex_wait_queue(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_pi_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_pi_owner(uaddr2, &q, !ret);
- /*
- * If fixup_pi_owner() returned an error, propagate that. If it
- * acquired the lock, clear -ETIMEDOUT or -EINTR.
- */
- if (res)
- ret = (res < 0) ? res : 0;
-
- futex_unqueue_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;
-}
-
/* Constants for the pending_op argument of handle_futex_death */
#define HANDLE_DEATH_PENDING true
#define HANDLE_DEATH_LIST false
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -3,6 +3,8 @@
#define _FUTEX_H
#include <linux/futex.h>
+#include <linux/sched/wake_q.h>
+
#include <asm/futex.h>
/*
@@ -118,22 +120,69 @@ enum futex_access {
extern int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
enum futex_access rw);
-extern struct futex_hash_bucket *futex_hash(union futex_key *key);
-
extern struct hrtimer_sleeper *
futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
int flags, u64 range_ns);
+extern struct futex_hash_bucket *futex_hash(union futex_key *key);
+
+/**
+ * futex_match - 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 futex_match(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);
+}
+
+extern int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
+ struct futex_q *q, struct futex_hash_bucket **hb);
+extern void futex_wait_queue(struct futex_hash_bucket *hb, struct futex_q *q,
+ struct hrtimer_sleeper *timeout);
+extern void futex_wake_mark(struct wake_q_head *wake_q, struct futex_q *q);
+
extern int fault_in_user_writeable(u32 __user *uaddr);
extern int futex_cmpxchg_value_locked(u32 *curval, u32 __user *uaddr, u32 uval, u32 newval);
extern int futex_get_value_locked(u32 *dest, u32 __user *from);
extern struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, union futex_key *key);
+extern void __futex_unqueue(struct futex_q *q);
extern void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb);
extern void futex_unqueue_pi(struct futex_q *q);
extern void wait_for_owner_exiting(int ret, struct task_struct *exiting);
+/*
+ * Reflects a new waiter being added to the waitqueue.
+ */
+static inline void futex_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 futex_hb_waiters_dec(struct futex_hash_bucket *hb)
+{
+#ifdef CONFIG_SMP
+ atomic_dec(&hb->waiters);
+#endif
+}
+
extern struct futex_hash_bucket *futex_q_lock(struct futex_q *q);
extern void futex_q_unlock(struct futex_hash_bucket *hb);
@@ -150,6 +199,30 @@ extern void get_pi_state(struct futex_pi
extern void put_pi_state(struct futex_pi_state *pi_state);
extern int fixup_pi_owner(u32 __user *uaddr, struct futex_q *q, int locked);
+/*
+ * 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);
+}
+
/* syscalls */
extern int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, u32
--- /dev/null
+++ b/kernel/futex/requeue.c
@@ -0,0 +1,897 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/sched/signal.h>
+
+#include "futex.h"
+#include "../locking/rtmutex_common.h"
+
+/*
+ * 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,
+};
+
+const struct futex_q futex_q_init = {
+ /* list gets initialized in futex_queue()*/
+ .key = FUTEX_KEY_INIT,
+ .bitset = FUTEX_BITSET_MATCH_ANY,
+ .requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE),
+};
+
+/**
+ * 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);
+ futex_hb_waiters_dec(hb1);
+ futex_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;
+
+ __futex_unqueue(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 (futex_get_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 (!futex_match(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
+ */
+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 && futex_match(&key1, &key2))
+ return -EINVAL;
+
+ hb1 = futex_hash(&key1);
+ hb2 = futex_hash(&key2);
+
+retry_private:
+ futex_hb_waiters_inc(hb2);
+ double_lock_hb(hb1, hb2);
+
+ if (likely(cmpval != NULL)) {
+ u32 curval;
+
+ ret = futex_get_value_locked(&curval, uaddr1);
+
+ if (unlikely(ret)) {
+ double_unlock_hb(hb1, hb2);
+ futex_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);
+ futex_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);
+ futex_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 (!futex_match(&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)
+ futex_wake_mark(&wake_q, this);
+ else
+ requeue_futex(this, hb1, hb2, &key2);
+ continue;
+ }
+
+ /* Ensure we requeue to the expected futex for requeue_pi. */
+ if (!futex_match(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);
+ futex_hb_waiters_dec(hb2);
+ return ret ? ret : task_count;
+}
+
+/**
+ * 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);
+ futex_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() 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
+ */
+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 (futex_match(&q.key, &key2)) {
+ futex_q_unlock(hb);
+ ret = -EINVAL;
+ goto out;
+ }
+
+ /* Queue the futex_q, drop the hb lock, wait for wakeup. */
+ futex_wait_queue(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_pi_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_pi_owner(uaddr2, &q, !ret);
+ /*
+ * If fixup_pi_owner() returned an error, propagate that. If it
+ * acquired the lock, clear -ETIMEDOUT or -EINTR.
+ */
+ if (res)
+ ret = (res < 0) ? res : 0;
+
+ futex_unqueue_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;
+}
+
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