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Message-ID: <20210715173145.GC4717@worktop.programming.kicks-ass.net>
Date: Thu, 15 Jul 2021 19:31:45 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Juri Lelli <juri.lelli@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Davidlohr Bueso <dave@...olabs.net>, thellstrom@...are.com,
dev@...ankhorst.nl, chris@...is-wilson.co.uk
Subject: Re: [patch 33/50] locking/mutex: Introduce _mutex_t
On Tue, Jul 13, 2021 at 05:11:27PM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
>
> PREEMPT_RT replaces 'struct mutex' with a rtmutex based variant so all
> mutex operations are included into the priority inheritance scheme.
>
> But a complete replacement of the mutex implementation would require to
> reimplement ww_mutex on top of the rtmutex based variant. That has been
> tried, but the outcome was suboptimal.
>
> As ww_mutex is mostly used in DRM and the code pathes are not really
> relevant to typical RT applications, it's also hard to argue for a full
> reimplementation which can't even share code with the regular ww_mutex code
> adding the risk of diversion and different bugs in both code bases.
>
> The alternative solution is to make it possible to compile the ww_mutex
> specific part of the regular mutex implementation as is on RT and have a
> rtmutex based 'struct mutex' variant.
>
> As the regular mutex and ww_mutex implementation are tightly coupled
> (ww_mutex has a 'struct mutex' inside) and share a lot of code (ww_mutex is
> mostly an extension) a simple replacement of 'struct mutex' does not work.
>
> To solve this attach a typedef to 'struct mutex': _mutex_t
I couldn't let go of this, sorry... the below compiles and might even
work.
I'll try and complete it tomorrow and add copy of the ww_mutex selftest
for ww_rt_mutex to see what it does.
(it includes a bunch of the cleanup/prep patches from this series)
---
include/linux/mutex.h | 26 +-
include/linux/ww_mutex.h | 35 ++-
kernel/locking/mutex-debug.c | 5 +-
kernel/locking/mutex-debug.h | 29 ---
kernel/locking/mutex.c | 423 ++-----------------------------
kernel/locking/mutex.h | 33 ++-
kernel/locking/rtmutex.c | 81 +++++-
kernel/locking/rtmutex_common.h | 5 +-
kernel/locking/ww_mutex.h | 544 ++++++++++++++++++++++++++++++++++++++++
9 files changed, 703 insertions(+), 478 deletions(-)
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index e19323521f9c..52476efc9b04 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -20,9 +20,6 @@
#include <linux/osq_lock.h>
#include <linux/debug_locks.h>
-struct ww_class;
-struct ww_acquire_ctx;
-
/*
* Simple, straightforward mutexes with strict semantics:
*
@@ -53,7 +50,7 @@ struct ww_acquire_ctx;
*/
struct mutex {
atomic_long_t owner;
- spinlock_t wait_lock;
+ raw_spinlock_t wait_lock;
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
struct optimistic_spin_queue osq; /* Spinner MCS lock */
#endif
@@ -66,27 +63,6 @@ struct mutex {
#endif
};
-struct ww_mutex {
- struct mutex base;
- struct ww_acquire_ctx *ctx;
-#ifdef CONFIG_DEBUG_MUTEXES
- struct ww_class *ww_class;
-#endif
-};
-
-/*
- * This is the control structure for tasks blocked on mutex,
- * which resides on the blocked task's kernel stack:
- */
-struct mutex_waiter {
- struct list_head list;
- struct task_struct *task;
- struct ww_acquire_ctx *ww_ctx;
-#ifdef CONFIG_DEBUG_MUTEXES
- void *magic;
-#endif
-};
-
#ifdef CONFIG_DEBUG_MUTEXES
#define __DEBUG_MUTEX_INITIALIZER(lockname) \
diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index b77f39f319ad..7fcf00bd177c 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -18,6 +18,11 @@
#define __LINUX_WW_MUTEX_H
#include <linux/mutex.h>
+#include <linux/rtmutex.h>
+
+#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_DEBUG_RT_MUTEXES)
+#define DEBUG_WW_MUTEXES
+#endif
struct ww_class {
atomic_long_t stamp;
@@ -28,13 +33,29 @@ struct ww_class {
unsigned int is_wait_die;
};
+struct ww_mutex {
+ struct mutex base;
+ struct ww_acquire_ctx *ctx;
+#ifdef DEBUG_WW_MUTEXES
+ struct ww_class *ww_class;
+#endif
+};
+
+struct ww_rt_mutex {
+ struct rt_mutex base;
+ struct ww_acquire_ctx *ctx;
+#ifdef DEBUG_WW_MUTEXES
+ struct ww_class *ww_class;
+#endif
+};
+
struct ww_acquire_ctx {
struct task_struct *task;
unsigned long stamp;
unsigned int acquired;
unsigned short wounded;
unsigned short is_wait_die;
-#ifdef CONFIG_DEBUG_MUTEXES
+#ifdef DEBUG_WW_MUTEXES
unsigned int done_acquire;
struct ww_class *ww_class;
struct ww_mutex *contending_lock;
@@ -76,7 +97,7 @@ static inline void ww_mutex_init(struct ww_mutex *lock,
{
__mutex_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
lock->ctx = NULL;
-#ifdef CONFIG_DEBUG_MUTEXES
+#ifdef DEBUG_WW_MUTEXES
lock->ww_class = ww_class;
#endif
}
@@ -113,7 +134,7 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
ctx->acquired = 0;
ctx->wounded = false;
ctx->is_wait_die = ww_class->is_wait_die;
-#ifdef CONFIG_DEBUG_MUTEXES
+#ifdef DEBUG_WW_MUTEXES
ctx->ww_class = ww_class;
ctx->done_acquire = 0;
ctx->contending_lock = NULL;
@@ -143,7 +164,7 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
*/
static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
{
-#ifdef CONFIG_DEBUG_MUTEXES
+#ifdef DEBUG_WW_MUTEXES
lockdep_assert_held(ctx);
DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
@@ -163,7 +184,7 @@ static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
#ifdef CONFIG_DEBUG_LOCK_ALLOC
mutex_release(&ctx->dep_map, _THIS_IP_);
#endif
-#ifdef CONFIG_DEBUG_MUTEXES
+#ifdef DEBUG_WW_MUTEXES
DEBUG_LOCKS_WARN_ON(ctx->acquired);
if (!IS_ENABLED(CONFIG_PROVE_LOCKING))
/*
@@ -269,7 +290,7 @@ static inline void
ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
int ret;
-#ifdef CONFIG_DEBUG_MUTEXES
+#ifdef DEBUG_WW_MUTEXES
DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
#endif
ret = ww_mutex_lock(lock, ctx);
@@ -305,7 +326,7 @@ static inline int __must_check
ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
-#ifdef CONFIG_DEBUG_MUTEXES
+#ifdef DEBUG_WW_MUTEXES
DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
#endif
return ww_mutex_lock_interruptible(lock, ctx);
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index db9301591e3f..30dc4faba524 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -1,6 +1,4 @@
/*
- * kernel/mutex-debug.c
- *
* Debugging code for mutexes
*
* Started by Ingo Molnar:
@@ -22,7 +20,7 @@
#include <linux/interrupt.h>
#include <linux/debug_locks.h>
-#include "mutex-debug.h"
+#include "mutex.h"
/*
* Must be called with lock->wait_lock held.
@@ -32,6 +30,7 @@ void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
memset(waiter, MUTEX_DEBUG_INIT, sizeof(*waiter));
waiter->magic = waiter;
INIT_LIST_HEAD(&waiter->list);
+ waiter.ww_ctx = MUTEX_POISON_WW_CTX;
}
void debug_mutex_wake_waiter(struct mutex *lock, struct mutex_waiter *waiter)
diff --git a/kernel/locking/mutex-debug.h b/kernel/locking/mutex-debug.h
deleted file mode 100644
index 53e631e1d76d..000000000000
--- a/kernel/locking/mutex-debug.h
+++ /dev/null
@@ -1,29 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * Mutexes: blocking mutual exclusion locks
- *
- * started by Ingo Molnar:
- *
- * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@...hat.com>
- *
- * This file contains mutex debugging related internal declarations,
- * prototypes and inline functions, for the CONFIG_DEBUG_MUTEXES case.
- * More details are in kernel/mutex-debug.c.
- */
-
-/*
- * This must be called with lock->wait_lock held.
- */
-extern void debug_mutex_lock_common(struct mutex *lock,
- struct mutex_waiter *waiter);
-extern void debug_mutex_wake_waiter(struct mutex *lock,
- struct mutex_waiter *waiter);
-extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
-extern void debug_mutex_add_waiter(struct mutex *lock,
- struct mutex_waiter *waiter,
- struct task_struct *task);
-extern void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
- struct task_struct *task);
-extern void debug_mutex_unlock(struct mutex *lock);
-extern void debug_mutex_init(struct mutex *lock, const char *name,
- struct lock_class_key *key);
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index d2df5e68b503..4d50b7b774d8 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -30,17 +30,13 @@
#include <linux/debug_locks.h>
#include <linux/osq_lock.h>
-#ifdef CONFIG_DEBUG_MUTEXES
-# include "mutex-debug.h"
-#else
-# include "mutex.h"
-#endif
+#include "mutex.h"
void
__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
{
atomic_long_set(&lock->owner, 0);
- spin_lock_init(&lock->wait_lock);
+ raw_spin_lock_init(&lock->wait_lock);
INIT_LIST_HEAD(&lock->wait_list);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
osq_lock_init(&lock->osq);
@@ -286,215 +282,7 @@ void __sched mutex_lock(struct mutex *lock)
EXPORT_SYMBOL(mutex_lock);
#endif
-/*
- * Wait-Die:
- * The newer transactions are killed when:
- * It (the new transaction) makes a request for a lock being held
- * by an older transaction.
- *
- * Wound-Wait:
- * The newer transactions are wounded when:
- * An older transaction makes a request for a lock being held by
- * the newer transaction.
- */
-
-/*
- * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
- * it.
- */
-static __always_inline void
-ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
-{
-#ifdef CONFIG_DEBUG_MUTEXES
- /*
- * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
- * but released with a normal mutex_unlock in this call.
- *
- * This should never happen, always use ww_mutex_unlock.
- */
- DEBUG_LOCKS_WARN_ON(ww->ctx);
-
- /*
- * Not quite done after calling ww_acquire_done() ?
- */
- DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
-
- if (ww_ctx->contending_lock) {
- /*
- * After -EDEADLK you tried to
- * acquire a different ww_mutex? Bad!
- */
- DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
-
- /*
- * You called ww_mutex_lock after receiving -EDEADLK,
- * but 'forgot' to unlock everything else first?
- */
- DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
- ww_ctx->contending_lock = NULL;
- }
-
- /*
- * Naughty, using a different class will lead to undefined behavior!
- */
- DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
-#endif
- ww_ctx->acquired++;
- ww->ctx = ww_ctx;
-}
-
-/*
- * Determine if context @a is 'after' context @b. IOW, @a is a younger
- * transaction than @b and depending on algorithm either needs to wait for
- * @b or die.
- */
-static inline bool __sched
-__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
-{
-
- return (signed long)(a->stamp - b->stamp) > 0;
-}
-
-/*
- * Wait-Die; wake a younger waiter context (when locks held) such that it can
- * die.
- *
- * Among waiters with context, only the first one can have other locks acquired
- * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
- * __ww_mutex_check_kill() wake any but the earliest context.
- */
-static bool __sched
-__ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
- struct ww_acquire_ctx *ww_ctx)
-{
- if (!ww_ctx->is_wait_die)
- return false;
-
- if (waiter->ww_ctx->acquired > 0 &&
- __ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
- debug_mutex_wake_waiter(lock, waiter);
- wake_up_process(waiter->task);
- }
-
- return true;
-}
-
-/*
- * Wound-Wait; wound a younger @hold_ctx if it holds the lock.
- *
- * Wound the lock holder if there are waiters with older transactions than
- * the lock holders. Even if multiple waiters may wound the lock holder,
- * it's sufficient that only one does.
- */
-static bool __ww_mutex_wound(struct mutex *lock,
- struct ww_acquire_ctx *ww_ctx,
- struct ww_acquire_ctx *hold_ctx)
-{
- struct task_struct *owner = __mutex_owner(lock);
-
- lockdep_assert_held(&lock->wait_lock);
-
- /*
- * Possible through __ww_mutex_add_waiter() when we race with
- * ww_mutex_set_context_fastpath(). In that case we'll get here again
- * through __ww_mutex_check_waiters().
- */
- if (!hold_ctx)
- return false;
-
- /*
- * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
- * it cannot go away because we'll have FLAG_WAITERS set and hold
- * wait_lock.
- */
- if (!owner)
- return false;
-
- if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
- hold_ctx->wounded = 1;
-
- /*
- * wake_up_process() paired with set_current_state()
- * inserts sufficient barriers to make sure @owner either sees
- * it's wounded in __ww_mutex_check_kill() or has a
- * wakeup pending to re-read the wounded state.
- */
- if (owner != current)
- wake_up_process(owner);
-
- return true;
- }
-
- return false;
-}
-
-/*
- * We just acquired @lock under @ww_ctx, if there are later contexts waiting
- * behind us on the wait-list, check if they need to die, or wound us.
- *
- * See __ww_mutex_add_waiter() for the list-order construction; basically the
- * list is ordered by stamp, smallest (oldest) first.
- *
- * This relies on never mixing wait-die/wound-wait on the same wait-list;
- * which is currently ensured by that being a ww_class property.
- *
- * The current task must not be on the wait list.
- */
-static void __sched
-__ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
-{
- struct mutex_waiter *cur;
-
- lockdep_assert_held(&lock->wait_lock);
-
- list_for_each_entry(cur, &lock->wait_list, list) {
- if (!cur->ww_ctx)
- continue;
-
- if (__ww_mutex_die(lock, cur, ww_ctx) ||
- __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
- break;
- }
-}
-
-/*
- * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
- * and wake up any waiters so they can recheck.
- */
-static __always_inline void
-ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
-{
- ww_mutex_lock_acquired(lock, ctx);
-
- /*
- * The lock->ctx update should be visible on all cores before
- * the WAITERS check is done, otherwise contended waiters might be
- * missed. The contended waiters will either see ww_ctx == NULL
- * and keep spinning, or it will acquire wait_lock, add itself
- * to waiter list and sleep.
- */
- smp_mb(); /* See comments above and below. */
-
- /*
- * [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
- * MB MB
- * [R] MUTEX_FLAG_WAITERS [R] ww->ctx
- *
- * The memory barrier above pairs with the memory barrier in
- * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
- * and/or !empty list.
- */
- if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
- return;
-
- /*
- * Uh oh, we raced in fastpath, check if any of the waiters need to
- * die or wound us.
- */
- spin_lock(&lock->base.wait_lock);
- __ww_mutex_check_waiters(&lock->base, ctx);
- spin_unlock(&lock->base.wait_lock);
-}
+#include "ww_mutex.h"
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
@@ -752,173 +540,13 @@ EXPORT_SYMBOL(mutex_unlock);
* This function must not be used in interrupt context. Unlocking
* of a unlocked mutex is not allowed.
*/
-void __sched ww_mutex_unlock(struct ww_mutex *lock)
+void ww_mutex_unlock(struct WW_MUTEX *lock)
{
- /*
- * The unlocking fastpath is the 0->1 transition from 'locked'
- * into 'unlocked' state:
- */
- if (lock->ctx) {
-#ifdef CONFIG_DEBUG_MUTEXES
- DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
-#endif
- if (lock->ctx->acquired > 0)
- lock->ctx->acquired--;
- lock->ctx = NULL;
- }
-
+ __ww_mutex_unlock(lock);
mutex_unlock(&lock->base);
}
EXPORT_SYMBOL(ww_mutex_unlock);
-
-static __always_inline int __sched
-__ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
-{
- if (ww_ctx->acquired > 0) {
-#ifdef CONFIG_DEBUG_MUTEXES
- struct ww_mutex *ww;
-
- ww = container_of(lock, struct ww_mutex, base);
- DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
- ww_ctx->contending_lock = ww;
-#endif
- return -EDEADLK;
- }
-
- return 0;
-}
-
-
-/*
- * Check the wound condition for the current lock acquire.
- *
- * Wound-Wait: If we're wounded, kill ourself.
- *
- * Wait-Die: If we're trying to acquire a lock already held by an older
- * context, kill ourselves.
- *
- * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
- * look at waiters before us in the wait-list.
- */
-static inline int __sched
-__ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
- struct ww_acquire_ctx *ctx)
-{
- struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
- struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
- struct mutex_waiter *cur;
-
- if (ctx->acquired == 0)
- return 0;
-
- if (!ctx->is_wait_die) {
- if (ctx->wounded)
- return __ww_mutex_kill(lock, ctx);
-
- return 0;
- }
-
- if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
- return __ww_mutex_kill(lock, ctx);
-
- /*
- * If there is a waiter in front of us that has a context, then its
- * stamp is earlier than ours and we must kill ourself.
- */
- cur = waiter;
- list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
- if (!cur->ww_ctx)
- continue;
-
- return __ww_mutex_kill(lock, ctx);
- }
-
- return 0;
-}
-
-/*
- * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
- * first. Such that older contexts are preferred to acquire the lock over
- * younger contexts.
- *
- * Waiters without context are interspersed in FIFO order.
- *
- * Furthermore, for Wait-Die kill ourself immediately when possible (there are
- * older contexts already waiting) to avoid unnecessary waiting and for
- * Wound-Wait ensure we wound the owning context when it is younger.
- */
-static inline int __sched
-__ww_mutex_add_waiter(struct mutex_waiter *waiter,
- struct mutex *lock,
- struct ww_acquire_ctx *ww_ctx)
-{
- struct mutex_waiter *cur;
- struct list_head *pos;
- bool is_wait_die;
-
- if (!ww_ctx) {
- __mutex_add_waiter(lock, waiter, &lock->wait_list);
- return 0;
- }
-
- is_wait_die = ww_ctx->is_wait_die;
-
- /*
- * Add the waiter before the first waiter with a higher stamp.
- * Waiters without a context are skipped to avoid starving
- * them. Wait-Die waiters may die here. Wound-Wait waiters
- * never die here, but they are sorted in stamp order and
- * may wound the lock holder.
- */
- pos = &lock->wait_list;
- list_for_each_entry_reverse(cur, &lock->wait_list, list) {
- if (!cur->ww_ctx)
- continue;
-
- if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
- /*
- * Wait-Die: if we find an older context waiting, there
- * is no point in queueing behind it, as we'd have to
- * die the moment it would acquire the lock.
- */
- if (is_wait_die) {
- int ret = __ww_mutex_kill(lock, ww_ctx);
-
- if (ret)
- return ret;
- }
-
- break;
- }
-
- pos = &cur->list;
-
- /* Wait-Die: ensure younger waiters die. */
- __ww_mutex_die(lock, cur, ww_ctx);
- }
-
- __mutex_add_waiter(lock, waiter, pos);
-
- /*
- * Wound-Wait: if we're blocking on a mutex owned by a younger context,
- * wound that such that we might proceed.
- */
- if (!is_wait_die) {
- struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
-
- /*
- * See ww_mutex_set_context_fastpath(). Orders setting
- * MUTEX_FLAG_WAITERS vs the ww->ctx load,
- * such that either we or the fastpath will wound @ww->ctx.
- */
- smp_mb();
- __ww_mutex_wound(lock, ww_ctx, ww->ctx);
- }
-
- return 0;
-}
-
/*
* Lock a mutex (possibly interruptible), slowpath:
*/
@@ -953,6 +581,10 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
*/
if (ww_ctx->acquired == 0)
ww_ctx->wounded = 0;
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ nest_lock = &ww_ctx->dep_map;
+#endif
}
preempt_disable();
@@ -968,7 +600,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
return 0;
}
- spin_lock(&lock->wait_lock);
+ raw_spin_lock(&lock->wait_lock);
/*
* After waiting to acquire the wait_lock, try again.
*/
@@ -987,10 +619,6 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
/* add waiting tasks to the end of the waitqueue (FIFO): */
__mutex_add_waiter(lock, &waiter, &lock->wait_list);
-
-#ifdef CONFIG_DEBUG_MUTEXES
- waiter.ww_ctx = MUTEX_POISON_WW_CTX;
-#endif
} else {
/*
* Add in stamp order, waking up waiters that must kill
@@ -999,8 +627,6 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
if (ret)
goto err_early_kill;
-
- waiter.ww_ctx = ww_ctx;
}
waiter.task = current;
@@ -1032,7 +658,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
goto err;
}
- spin_unlock(&lock->wait_lock);
+ raw_spin_unlock(&lock->wait_lock);
schedule_preempt_disabled();
/*
@@ -1055,9 +681,9 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
(first && mutex_optimistic_spin(lock, ww_ctx, &waiter)))
break;
- spin_lock(&lock->wait_lock);
+ raw_spin_lock(&lock->wait_lock);
}
- spin_lock(&lock->wait_lock);
+ raw_spin_lock(&lock->wait_lock);
acquired:
__set_current_state(TASK_RUNNING);
@@ -1082,7 +708,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
if (ww_ctx)
ww_mutex_lock_acquired(ww, ww_ctx);
- spin_unlock(&lock->wait_lock);
+ raw_spin_unlock(&lock->wait_lock);
preempt_enable();
return 0;
@@ -1090,7 +716,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
__set_current_state(TASK_RUNNING);
__mutex_remove_waiter(lock, &waiter);
err_early_kill:
- spin_unlock(&lock->wait_lock);
+ raw_spin_unlock(&lock->wait_lock);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, ip);
preempt_enable();
@@ -1106,10 +732,9 @@ __mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
static int __sched
__ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
- struct lockdep_map *nest_lock, unsigned long ip,
- struct ww_acquire_ctx *ww_ctx)
+ unsigned long ip, struct ww_acquire_ctx *ww_ctx)
{
- return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
+ return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -1189,8 +814,7 @@ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
might_sleep();
ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
- 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
- ctx);
+ 0, _RET_IP_, ctx);
if (!ret && ctx && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
@@ -1205,8 +829,7 @@ ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
might_sleep();
ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
- 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
- ctx);
+ 0, _RET_IP_, ctx);
if (!ret && ctx && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
@@ -1259,7 +882,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
owner = old;
}
- spin_lock(&lock->wait_lock);
+ raw_spin_lock(&lock->wait_lock);
debug_mutex_unlock(lock);
if (!list_empty(&lock->wait_list)) {
/* get the first entry from the wait-list: */
@@ -1276,7 +899,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
if (owner & MUTEX_FLAG_HANDOFF)
__mutex_handoff(lock, next);
- spin_unlock(&lock->wait_lock);
+ raw_spin_unlock(&lock->wait_lock);
wake_up_q(&wake_q);
}
@@ -1380,7 +1003,7 @@ __mutex_lock_interruptible_slowpath(struct mutex *lock)
static noinline int __sched
__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
- return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
+ return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0,
_RET_IP_, ctx);
}
@@ -1388,7 +1011,7 @@ static noinline int __sched
__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
- return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
+ return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0,
_RET_IP_, ctx);
}
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index f0c710b1d192..8d1b0ee49062 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -5,11 +5,37 @@
* started by Ingo Molnar:
*
* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@...hat.com>
- *
- * This file contains mutex debugging related internal prototypes, for the
- * !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:
*/
+/*
+ * This is the control structure for tasks blocked on mutex, which resides
+ * on the blocked task's kernel stack:
+ */
+struct mutex_waiter {
+ struct list_head list;
+ struct task_struct *task;
+ struct ww_acquire_ctx *ww_ctx;
+#ifdef CONFIG_DEBUG_MUTEXES
+ void *magic;
+#endif
+};
+
+#ifdef CONFIG_DEBUG_MUTEXES
+extern void debug_mutex_lock_common(struct mutex *lock,
+ struct mutex_waiter *waiter);
+extern void debug_mutex_wake_waiter(struct mutex *lock,
+ struct mutex_waiter *waiter);
+extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
+extern void debug_mutex_add_waiter(struct mutex *lock,
+ struct mutex_waiter *waiter,
+ struct task_struct *task);
+extern void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+ struct task_struct *task);
+extern void debug_mutex_unlock(struct mutex *lock);
+extern void debug_mutex_init(struct mutex *lock, const char *name,
+ struct lock_class_key *key);
+#else /* CONFIG_DEBUG_MUTEXES */
+
#define debug_mutex_wake_waiter(lock, waiter) do { } while (0)
#define debug_mutex_free_waiter(waiter) do { } while (0)
#define debug_mutex_add_waiter(lock, waiter, ti) do { } while (0)
@@ -21,3 +47,4 @@ static inline void
debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
{
}
+#endif /* !CONFIG_DEBUG_MUTEXES */
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index b5d9bb5202c6..72b2a31f9af7 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -19,6 +19,7 @@
#include <linux/sched/wake_q.h>
#include <linux/sched/debug.h>
#include <linux/timer.h>
+#include <linux/ww_mutex.h>
#include "rtmutex_common.h"
@@ -1125,6 +1126,9 @@ void __sched rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
waiter->task = NULL;
}
+#define WW_RT
+#include "ww_mutex.h"
+
/**
* __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
* @lock: the rt_mutex to take
@@ -1136,6 +1140,7 @@ void __sched rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
* Must be called with lock->wait_lock held and interrupts disabled
*/
static int __sched __rt_mutex_slowlock(struct rt_mutex *lock, unsigned int state,
+ struct ww_acquire_ctx *ww_ctx,
struct hrtimer_sleeper *timeout,
struct rt_mutex_waiter *waiter)
{
@@ -1155,6 +1160,12 @@ static int __sched __rt_mutex_slowlock(struct rt_mutex *lock, unsigned int state
break;
}
+ if (ww_ctx) {
+ ret = __ww_mutex_check_kill(lock, waiter, ww_ctx);
+ if (ret)
+ break;
+ }
+
raw_spin_unlock_irq(&lock->wait_lock);
schedule();
@@ -1192,8 +1203,10 @@ static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
*/
static int __sched rt_mutex_slowlock(struct rt_mutex *lock, unsigned int state,
struct hrtimer_sleeper *timeout,
+ struct ww_acquire_ctx *ww_ctx,
enum rtmutex_chainwalk chwalk)
{
+ struct ww_rt_mutex *ww = container_of(lock, struct ww_rt_mutex, base);
struct rt_mutex_waiter waiter;
unsigned long flags;
int ret = 0;
@@ -1212,6 +1225,10 @@ static int __sched rt_mutex_slowlock(struct rt_mutex *lock, unsigned int state,
/* Try to acquire the lock again: */
if (try_to_take_rt_mutex(lock, current, NULL)) {
+ if (ww_ctx) {
+ __ww_mutex_check_waiters(lock, ww_ctx);
+ ww_mutex_lock_acquired(ww, ww_ctx);
+ }
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
return 0;
}
@@ -1224,11 +1241,25 @@ static int __sched rt_mutex_slowlock(struct rt_mutex *lock, unsigned int state,
ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
- if (likely(!ret))
+ if (!ret && ww_ctx) {
+ /* additional W/W fails */
+ ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
+ }
+
+ if (likely(!ret)) {
/* sleep on the mutex */
- ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
+ ret = __rt_mutex_slowlock(lock, state, ww_ctx, timeout, &waiter);
+ }
- if (unlikely(ret)) {
+ if (likely(!ret)) {
+ /* acquired the lock */
+ if (ww_ctx) {
+ if (!ww_ctx->is_wait_die)
+ __ww_mutex_check_waiters(lock, ww_ctx);
+ ww_mutex_lock_acquired(ww, ww_ctx);
+ }
+ } else {
+ /* failed */
__set_current_state(TASK_RUNNING);
remove_waiter(lock, &waiter);
rt_mutex_handle_deadlock(ret, chwalk, &waiter);
@@ -1377,22 +1408,45 @@ static void __sched rt_mutex_slowunlock(struct rt_mutex *lock)
* architecture does not support cmpxchg or when debugging is enabled.
*/
static __always_inline int __rt_mutex_lock(struct rt_mutex *lock, long state,
+ struct ww_acquire_ctx *ww_ctx,
unsigned int subclass)
{
+ struct ww_rt_mutex *ww = container_of(lock, struct ww_rt_mutex, base);
+ struct lockdep_map *nest_lock __maybe_unused = NULL;
int ret;
+ if (ww_ctx) {
+ if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
+ return -EALREADY;
+
+ if (ww_ctx->acquired == 0)
+ ww_ctx->wounded = 0;
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ nest_lock = &ww_ctx->dep_map;
+#endif
+ }
+
might_sleep();
- mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
+ mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, _RET_IP_);
- if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
+ if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
+ if (ww_ctx)
+ ww_mutex_set_context_fastpath(ww, ww_ctx);
return 0;
+ }
- ret = rt_mutex_slowlock(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
+ ret = rt_mutex_slowlock(lock, state, NULL, ww_ctx, RT_MUTEX_MIN_CHAINWALK);
if (ret)
mutex_release(&lock->dep_map, _RET_IP_);
return ret;
}
+void ww_rt_mutex_lock(struct ww_rt_mutex *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ __rt_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, ww_ctx, 0);
+}
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/**
* rt_mutex_lock_nested - lock a rt_mutex
@@ -1402,7 +1456,7 @@ static __always_inline int __rt_mutex_lock(struct rt_mutex *lock, long state,
*/
void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
{
- __rt_mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass);
+ __rt_mutex_lock(lock, TASK_UNINTERRUPTIBLE, NULL, subclass);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
@@ -1415,7 +1469,7 @@ EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
*/
void __sched rt_mutex_lock(struct rt_mutex *lock)
{
- __rt_mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0);
+ __rt_mutex_lock(lock, TASK_UNINTERRUPTIBLE, NULL, 0);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock);
#endif
@@ -1431,7 +1485,7 @@ EXPORT_SYMBOL_GPL(rt_mutex_lock);
*/
int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
{
- return __rt_mutex_lock(lock, TASK_INTERRUPTIBLE, 0);
+ return __rt_mutex_lock(lock, TASK_INTERRUPTIBLE, NULL, 0);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
@@ -1484,6 +1538,13 @@ void __sched rt_mutex_unlock(struct rt_mutex *lock)
}
EXPORT_SYMBOL_GPL(rt_mutex_unlock);
+void ww_rt_mutex_unlock(struct ww_rt_mutex *lock)
+{
+ __ww_mutex_unlock(lock);
+ rt_mutex_unlock(&lock->base);
+}
+EXPORT_SYMBOL_GPL(ww_rt_mutex_unlock);
+
/*
* Futex variants, must not use fastpath.
*/
@@ -1708,7 +1769,7 @@ int __sched rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
raw_spin_lock_irq(&lock->wait_lock);
/* sleep on the mutex */
set_current_state(TASK_INTERRUPTIBLE);
- ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
+ ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, NULL, to, waiter);
/*
* try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
* have to fix that up.
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index a90c22abdbca..792ff1227ccb 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -35,6 +35,7 @@ struct rt_mutex_waiter {
struct rt_mutex *lock;
int prio;
u64 deadline;
+ struct ww_acquire_ctx *ww_ctx;
};
/*
@@ -151,8 +152,10 @@ static inline void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock)
static inline void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
{
- if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
+ if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES)) {
memset(waiter, 0x11, sizeof(*waiter));
+ waiter->ww_ctx = MUTEX_POISON_WW_CTX;
+ }
}
static inline void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
new file mode 100644
index 000000000000..a65d844c3735
--- /dev/null
+++ b/kernel/locking/ww_mutex.h
@@ -0,0 +1,544 @@
+
+#ifndef WW_RT
+
+#define WW_MUTEX ww_mutex
+#define MUTEX mutex
+#define MUTEX_WAITER mutex_waiter
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_first(struct MUTEX *lock)
+{
+ struct MUTEX_WAITER *w;
+
+ w = list_first_entry(&lock->wait_list, struct MUTEX_WAITER, list);
+ if (list_entry_is_head(w, &lock->wait_list, list))
+ return NULL;
+
+ return w;
+}
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_next(struct MUTEX *lock, struct MUTEX_WAITER *w)
+{
+ w = list_next_entry(w, list);
+ if (list_entry_is_head(w, &lock->wait_list, list))
+ return NULL;
+
+ return w;
+}
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_prev(struct MUTEX *lock, struct MUTEX_WAITER *w)
+{
+ w = list_prev_entry(w, list);
+ if (list_entry_is_head(w, &lock->wait_list, list))
+ return NULL;
+
+ return w;
+}
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_last(struct MUTEX *lock)
+{
+ struct MUTEX_WAITER *w;
+
+ w = list_last_entry(&lock->wait_list, struct MUTEX_WAITER, list);
+ if (list_entry_is_head(w, &lock->wait_list, list))
+ return NULL;
+
+ return w;
+}
+
+static inline void
+__ww_waiter_add(struct MUTEX *lock, struct MUTEX_WAITER *waiter, struct MUTEX_WAITER *pos)
+{
+ struct list_head *p;
+
+ if (!pos)
+ p = &lock->wait_list;
+ else
+ p = &pos->list;
+
+ __mutex_add_waiter(lock, waiter, p);
+}
+
+static inline struct task_struct *
+__ww_mutex_owner(struct MUTEX *lock)
+{
+ return __mutex_owner(lock);
+}
+
+static inline bool
+__ww_mutex_has_waiters(struct MUTEX *lock)
+{
+ return atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS;
+}
+
+#else /* WW_RT */
+
+#define WW_MUTEX ww_rt_mutex
+#define MUTEX rt_mutex
+#define MUTEX_WAITER rt_mutex_waiter
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_first(struct MUTEX *lock)
+{
+ struct rb_node *n = rb_first(&lock->waiters.rb_root);
+ if (!n)
+ return NULL;
+ return rb_entry(n, struct MUTEX_WAITER, tree_entry);
+}
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_next(struct MUTEX *lock, struct MUTEX_WAITER *w)
+{
+ struct rb_node *n = rb_next(&w->tree_entry);
+ if (!n)
+ return NULL;
+ return rb_entry(n, struct MUTEX_WAITER, tree_entry);
+}
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_prev(struct MUTEX *lock, struct MUTEX_WAITER *w)
+{
+ struct rb_node *n = rb_prev(&w->tree_entry);
+ if (!n)
+ return NULL;
+ return rb_entry(n, struct MUTEX_WAITER, tree_entry);
+}
+
+static inline struct MUTEX_WAITER *
+__ww_waiter_last(struct MUTEX *lock)
+{
+ struct rb_node *n = rb_last(&lock->waiters.rb_root);
+ if (!n)
+ return NULL;
+ return rb_entry(n, struct MUTEX_WAITER, tree_entry);
+}
+
+static inline void
+__ww_waiter_add(struct MUTEX *lock, struct MUTEX_WAITER *waiter, struct MUTEX_WAITER *pos)
+{
+ /* RT unconditionally adds the waiter first and then removes it on error */
+}
+
+static inline struct task_struct *
+__ww_mutex_owner(struct MUTEX *lock)
+{
+ return rt_mutex_owner(lock);
+}
+
+static inline bool
+__ww_mutex_has_waiters(struct MUTEX *lock)
+{
+ return rt_mutex_has_waiters(lock);
+}
+
+#endif /* WW_RT */
+
+/*
+ * Wait-Die:
+ * The newer transactions are killed when:
+ * It (the new transaction) makes a request for a lock being held
+ * by an older transaction.
+ *
+ * Wound-Wait:
+ * The newer transactions are wounded when:
+ * An older transaction makes a request for a lock being held by
+ * the newer transaction.
+ */
+
+/*
+ * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
+ * it.
+ */
+static __always_inline void
+ww_mutex_lock_acquired(struct WW_MUTEX *ww, struct ww_acquire_ctx *ww_ctx)
+{
+#ifdef DEBUG_WW_MUTEXES
+ /*
+ * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
+ * but released with a normal mutex_unlock in this call.
+ *
+ * This should never happen, always use ww_mutex_unlock.
+ */
+ DEBUG_LOCKS_WARN_ON(ww->ctx);
+
+ /*
+ * Not quite done after calling ww_acquire_done() ?
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
+
+ if (ww_ctx->contending_lock) {
+ /*
+ * After -EDEADLK you tried to
+ * acquire a different ww_mutex? Bad!
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
+
+ /*
+ * You called ww_mutex_lock after receiving -EDEADLK,
+ * but 'forgot' to unlock everything else first?
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
+ ww_ctx->contending_lock = NULL;
+ }
+
+ /*
+ * Naughty, using a different class will lead to undefined behavior!
+ */
+ DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
+#endif
+ ww_ctx->acquired++;
+ ww->ctx = ww_ctx;
+}
+
+/*
+ * Determine if @a is 'less' than @b. IOW, either @a is a lower priority task
+ * or, when of equal priority, a younger transaction than @b.
+ *
+ * Depending on the algorithm, @a will either need to wait for @b, or die.
+ */
+static inline bool
+__ww_ctx_less(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
+{
+/*
+ * Can only do the RT prio for WW_RT because task->prio isn't stable due to PI,
+ * so the wait_list ordering will go wobbly. rt_mutex re-queues the waiter and
+ * isn't affected by this.
+ */
+#ifdef WW_RT
+ /* kernel prio; less is more */
+ int a_prio = a->task->prio;
+ int b_prio = b->task->prio;
+
+ if (dl_prio(a_prio) || dl_prio(b_prio)) {
+
+ if (a_prio > b_prio)
+ return true;
+
+ if (a_prio < b_prio)
+ return false;
+
+ /* equal static prio */
+
+ if (dl_prio(a_prio)) {
+ if (dl_time_before(b->task->dl.deadline,
+ a->task->dl.deadline))
+ return true;
+
+ if (dl_time_before(a->task->dl.deadline,
+ b->task->dl.deadline))
+ return false;
+ }
+
+ /* equal prio */
+ }
+#endif /* WW_RT */
+
+ /* FIFO order tie break -- bigger is younger */
+ return (signed long)(a->stamp - b->stamp) > 0;
+}
+
+/*
+ * Wait-Die; wake a lesser waiter context (when locks held) such that it can
+ * die.
+ *
+ * Among waiters with context, only the first one can have other locks acquired
+ * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
+ * __ww_mutex_check_kill() wake any but the earliest context.
+ */
+static bool
+__ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ if (!ww_ctx->is_wait_die)
+ return false;
+
+ if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) {
+#ifndef WW_RT
+ debug_mutex_wake_waiter(lock, waiter);
+#endif
+ wake_up_process(waiter->task);
+ }
+
+ return true;
+}
+
+/*
+ * Wound-Wait; wound a lesser @hold_ctx if it holds the lock.
+ *
+ * Wound the lock holder if there are waiters with more important transactions
+ * than the lock holders. Even if multiple waiters may wound the lock holder,
+ * it's sufficient that only one does.
+ */
+static bool __ww_mutex_wound(struct MUTEX *lock,
+ struct ww_acquire_ctx *ww_ctx,
+ struct ww_acquire_ctx *hold_ctx)
+{
+ struct task_struct *owner = __ww_mutex_owner(lock);
+
+ lockdep_assert_held(&lock->wait_lock);
+
+ /*
+ * Possible through __ww_mutex_add_waiter() when we race with
+ * ww_mutex_set_context_fastpath(). In that case we'll get here again
+ * through __ww_mutex_check_waiters().
+ */
+ if (!hold_ctx)
+ return false;
+
+ /*
+ * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
+ * it cannot go away because we'll have FLAG_WAITERS set and hold
+ * wait_lock.
+ */
+ if (!owner)
+ return false;
+
+ if (ww_ctx->acquired > 0 && __ww_ctx_less(hold_ctx, ww_ctx)) {
+ hold_ctx->wounded = 1;
+
+ /*
+ * wake_up_process() paired with set_current_state()
+ * inserts sufficient barriers to make sure @owner either sees
+ * it's wounded in __ww_mutex_check_kill() or has a
+ * wakeup pending to re-read the wounded state.
+ */
+ if (owner != current)
+ wake_up_process(owner);
+
+ return true;
+ }
+
+ return false;
+}
+
+/*
+ * We just acquired @lock under @ww_ctx, if there are lesser contexts waiting
+ * behind us on the wait-list, check if they need to die, or wound us.
+ *
+ * See __ww_mutex_add_waiter() for the list-order construction; basically the
+ * list is ordered by stamp, smallest (oldest) first.
+ *
+ * This relies on never mixing wait-die/wound-wait on the same wait-list;
+ * which is currently ensured by that being a ww_class property.
+ *
+ * The current task must not be on the wait list.
+ */
+static void
+__ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ struct MUTEX_WAITER *cur;
+
+ lockdep_assert_held(&lock->wait_lock);
+
+ for (cur = __ww_waiter_first(lock); cur;
+ cur = __ww_waiter_next(lock, cur)) {
+ if (!cur->ww_ctx)
+ continue;
+
+ if (__ww_mutex_die(lock, cur, ww_ctx) ||
+ __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
+ break;
+ }
+}
+
+/*
+ * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
+ * and wake up any waiters so they can recheck.
+ */
+static __always_inline void
+ww_mutex_set_context_fastpath(struct WW_MUTEX *lock, struct ww_acquire_ctx *ctx)
+{
+ ww_mutex_lock_acquired(lock, ctx);
+
+ /*
+ * The lock->ctx update should be visible on all cores before
+ * the WAITERS check is done, otherwise contended waiters might be
+ * missed. The contended waiters will either see ww_ctx == NULL
+ * and keep spinning, or it will acquire wait_lock, add itself
+ * to waiter list and sleep.
+ */
+ smp_mb(); /* See comments above and below. */
+
+ /*
+ * [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
+ * MB MB
+ * [R] MUTEX_FLAG_WAITERS [R] ww->ctx
+ *
+ * The memory barrier above pairs with the memory barrier in
+ * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
+ * and/or !empty list.
+ */
+ if (likely(!__ww_mutex_has_waiters(&lock->base)))
+ return;
+
+ /*
+ * Uh oh, we raced in fastpath, check if any of the waiters need to
+ * die or wound us.
+ */
+ raw_spin_lock(&lock->base.wait_lock);
+ __ww_mutex_check_waiters(&lock->base, ctx);
+ raw_spin_unlock(&lock->base.wait_lock);
+}
+
+static inline void
+__ww_mutex_unlock(struct WW_MUTEX *lock)
+{
+ if (lock->ctx) {
+#ifdef DEBUG_WW_MUTEXES
+ DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
+#endif
+ if (lock->ctx->acquired > 0)
+ lock->ctx->acquired--;
+ lock->ctx = NULL;
+ }
+}
+
+static __always_inline int
+__ww_mutex_kill(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ if (ww_ctx->acquired > 0) {
+#ifdef DEBUG_WW_MUTEXES
+ struct WW_MUTEX *ww;
+
+ ww = container_of(lock, struct WW_MUTEX, base);
+ DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
+ ww_ctx->contending_lock = ww;
+#endif
+ return -EDEADLK;
+ }
+
+ return 0;
+}
+
+/*
+ * Check the wound condition for the current lock acquire.
+ *
+ * Wound-Wait: If we're wounded, kill ourself.
+ *
+ * Wait-Die: If we're trying to acquire a lock already held by an older
+ * context, kill ourselves.
+ *
+ * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
+ * look at waiters before us in the wait-list.
+ */
+static inline int
+__ww_mutex_check_kill(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
+ struct ww_acquire_ctx *ctx)
+{
+ struct WW_MUTEX *ww = container_of(lock, struct WW_MUTEX, base);
+ struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
+ struct MUTEX_WAITER *cur;
+
+ if (ctx->acquired == 0)
+ return 0;
+
+ if (!ctx->is_wait_die) {
+ if (ctx->wounded)
+ return __ww_mutex_kill(lock, ctx);
+
+ return 0;
+ }
+
+ if (hold_ctx && __ww_ctx_less(ctx, hold_ctx))
+ return __ww_mutex_kill(lock, ctx);
+
+ /*
+ * If there is a waiter in front of us that has a context, then its
+ * stamp is earlier than ours and we must kill ourself.
+ */
+ for (cur = waiter; cur; cur = __ww_waiter_prev(lock, cur)) {
+ if (!cur->ww_ctx)
+ continue;
+
+ return __ww_mutex_kill(lock, ctx);
+ }
+
+ return 0;
+}
+
+/*
+ * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
+ * first. Such that older contexts are preferred to acquire the lock over
+ * younger contexts.
+ *
+ * Waiters without context are interspersed in FIFO order.
+ *
+ * Furthermore, for Wait-Die kill ourself immediately when possible (there are
+ * older contexts already waiting) to avoid unnecessary waiting and for
+ * Wound-Wait ensure we wound the owning context when it is younger.
+ */
+static inline int
+__ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
+ struct MUTEX *lock,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ struct MUTEX_WAITER *cur, *pos = NULL;
+ bool is_wait_die;
+
+ if (!ww_ctx) {
+ __ww_waiter_add(lock, waiter, NULL);
+ goto done;
+ }
+
+ is_wait_die = ww_ctx->is_wait_die;
+
+ /*
+ * Add the waiter before the first waiter with a higher stamp.
+ * Waiters without a context are skipped to avoid starving
+ * them. Wait-Die waiters may die here. Wound-Wait waiters
+ * never die here, but they are sorted in stamp order and
+ * may wound the lock holder.
+ */
+ for (cur = __ww_waiter_last(lock); cur;
+ cur = __ww_waiter_prev(lock, cur)) {
+
+ if (cur == waiter || !cur->ww_ctx)
+ continue;
+
+ if (__ww_ctx_less(ww_ctx, cur->ww_ctx)) {
+ /*
+ * Wait-Die: if we find an older context waiting, there
+ * is no point in queueing behind it, as we'd have to
+ * die the moment it would acquire the lock.
+ */
+ if (is_wait_die) {
+ int ret = __ww_mutex_kill(lock, ww_ctx);
+ if (ret)
+ return ret;
+ }
+
+ break;
+ }
+
+ pos = cur;
+
+ /* Wait-Die: ensure younger waiters die. */
+ __ww_mutex_die(lock, cur, ww_ctx);
+ }
+
+ __ww_waiter_add(lock, waiter, pos);
+
+ /*
+ * Wound-Wait: if we're blocking on a mutex owned by a younger context,
+ * wound that such that we might proceed.
+ */
+ if (!is_wait_die) {
+ struct WW_MUTEX *ww = container_of(lock, struct WW_MUTEX, base);
+
+ /*
+ * See ww_mutex_set_context_fastpath(). Orders setting
+ * MUTEX_FLAG_WAITERS vs the ww->ctx load,
+ * such that either we or the fastpath will wound @ww->ctx.
+ */
+ smp_mb();
+ __ww_mutex_wound(lock, ww_ctx, ww->ctx);
+ }
+
+done:
+ waiter->ww_ctx = ww_ctx;
+ return 0;
+}
+
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