4 * Mutexes: blocking mutual exclusion locks
6 * Started by Ingo Molnar:
8 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
10 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
11 * David Howells for suggestions and improvements.
13 * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
14 * from the -rt tree, where it was originally implemented for rtmutexes
15 * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
18 * Also see Documentation/mutex-design.txt.
20 #include <linux/mutex.h>
21 #include <linux/ww_mutex.h>
22 #include <linux/sched.h>
23 #include <linux/sched/rt.h>
24 #include <linux/export.h>
25 #include <linux/spinlock.h>
26 #include <linux/interrupt.h>
27 #include <linux/debug_locks.h>
30 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
31 * which forces all calls into the slowpath:
33 #ifdef CONFIG_DEBUG_MUTEXES
34 # include "mutex-debug.h"
35 # include <asm-generic/mutex-null.h>
38 # include <asm/mutex.h>
42 * A negative mutex count indicates that waiters are sleeping waiting for the
45 #define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) >= 0)
48 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
50 atomic_set(&lock->count, 1);
51 spin_lock_init(&lock->wait_lock);
52 INIT_LIST_HEAD(&lock->wait_list);
53 mutex_clear_owner(lock);
54 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
55 lock->spin_mlock = NULL;
58 debug_mutex_init(lock, name, key);
61 EXPORT_SYMBOL(__mutex_init);
63 #ifndef CONFIG_DEBUG_LOCK_ALLOC
65 * We split the mutex lock/unlock logic into separate fastpath and
66 * slowpath functions, to reduce the register pressure on the fastpath.
67 * We also put the fastpath first in the kernel image, to make sure the
68 * branch is predicted by the CPU as default-untaken.
70 static __used noinline void __sched
71 __mutex_lock_slowpath(atomic_t *lock_count);
74 * mutex_lock - acquire the mutex
75 * @lock: the mutex to be acquired
77 * Lock the mutex exclusively for this task. If the mutex is not
78 * available right now, it will sleep until it can get it.
80 * The mutex must later on be released by the same task that
81 * acquired it. Recursive locking is not allowed. The task
82 * may not exit without first unlocking the mutex. Also, kernel
83 * memory where the mutex resides mutex must not be freed with
84 * the mutex still locked. The mutex must first be initialized
85 * (or statically defined) before it can be locked. memset()-ing
86 * the mutex to 0 is not allowed.
88 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
89 * checks that will enforce the restrictions and will also do
90 * deadlock debugging. )
92 * This function is similar to (but not equivalent to) down().
94 void __sched mutex_lock(struct mutex *lock)
98 * The locking fastpath is the 1->0 transition from
99 * 'unlocked' into 'locked' state.
101 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
102 mutex_set_owner(lock);
105 EXPORT_SYMBOL(mutex_lock);
108 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
110 * In order to avoid a stampede of mutex spinners from acquiring the mutex
111 * more or less simultaneously, the spinners need to acquire a MCS lock
112 * first before spinning on the owner field.
114 * We don't inline mspin_lock() so that perf can correctly account for the
115 * time spent in this lock function.
118 struct mspin_node *next ;
119 int locked; /* 1 if lock acquired */
121 #define MLOCK(mutex) ((struct mspin_node **)&((mutex)->spin_mlock))
124 void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
126 struct mspin_node *prev;
132 prev = xchg(lock, node);
133 if (likely(prev == NULL)) {
138 ACCESS_ONCE(prev->next) = node;
140 /* Wait until the lock holder passes the lock down */
141 while (!ACCESS_ONCE(node->locked))
142 arch_mutex_cpu_relax();
145 static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node)
147 struct mspin_node *next = ACCESS_ONCE(node->next);
151 * Release the lock by setting it to NULL
153 if (cmpxchg(lock, node, NULL) == node)
155 /* Wait until the next pointer is set */
156 while (!(next = ACCESS_ONCE(node->next)))
157 arch_mutex_cpu_relax();
159 ACCESS_ONCE(next->locked) = 1;
164 * Mutex spinning code migrated from kernel/sched/core.c
167 static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
169 if (lock->owner != owner)
173 * Ensure we emit the owner->on_cpu, dereference _after_ checking
174 * lock->owner still matches owner, if that fails, owner might
175 * point to free()d memory, if it still matches, the rcu_read_lock()
176 * ensures the memory stays valid.
180 return owner->on_cpu;
184 * Look out! "owner" is an entirely speculative pointer
185 * access and not reliable.
188 int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
191 while (owner_running(lock, owner)) {
195 arch_mutex_cpu_relax();
200 * We break out the loop above on need_resched() and when the
201 * owner changed, which is a sign for heavy contention. Return
202 * success only when lock->owner is NULL.
204 return lock->owner == NULL;
208 * Initial check for entering the mutex spinning loop
210 static inline int mutex_can_spin_on_owner(struct mutex *lock)
216 retval = lock->owner->on_cpu;
219 * if lock->owner is not set, the mutex owner may have just acquired
220 * it and not set the owner yet or the mutex has been released.
226 static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
229 * mutex_unlock - release the mutex
230 * @lock: the mutex to be released
232 * Unlock a mutex that has been locked by this task previously.
234 * This function must not be used in interrupt context. Unlocking
235 * of a not locked mutex is not allowed.
237 * This function is similar to (but not equivalent to) up().
239 void __sched mutex_unlock(struct mutex *lock)
242 * The unlocking fastpath is the 0->1 transition from 'locked'
243 * into 'unlocked' state:
245 #ifndef CONFIG_DEBUG_MUTEXES
247 * When debugging is enabled we must not clear the owner before time,
248 * the slow path will always be taken, and that clears the owner field
249 * after verifying that it was indeed current.
251 mutex_clear_owner(lock);
253 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
256 EXPORT_SYMBOL(mutex_unlock);
259 * ww_mutex_unlock - release the w/w mutex
260 * @lock: the mutex to be released
262 * Unlock a mutex that has been locked by this task previously with any of the
263 * ww_mutex_lock* functions (with or without an acquire context). It is
264 * forbidden to release the locks after releasing the acquire context.
266 * This function must not be used in interrupt context. Unlocking
267 * of a unlocked mutex is not allowed.
269 void __sched ww_mutex_unlock(struct ww_mutex *lock)
272 * The unlocking fastpath is the 0->1 transition from 'locked'
273 * into 'unlocked' state:
276 #ifdef CONFIG_DEBUG_MUTEXES
277 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
279 if (lock->ctx->acquired > 0)
280 lock->ctx->acquired--;
284 #ifndef CONFIG_DEBUG_MUTEXES
286 * When debugging is enabled we must not clear the owner before time,
287 * the slow path will always be taken, and that clears the owner field
288 * after verifying that it was indeed current.
290 mutex_clear_owner(&lock->base);
292 __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath);
294 EXPORT_SYMBOL(ww_mutex_unlock);
296 static inline int __sched
297 __mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
299 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
300 struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx);
305 if (unlikely(ctx == hold_ctx))
308 if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
309 (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
310 #ifdef CONFIG_DEBUG_MUTEXES
311 DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
312 ctx->contending_lock = ww;
320 static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
321 struct ww_acquire_ctx *ww_ctx)
323 #ifdef CONFIG_DEBUG_MUTEXES
325 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
326 * but released with a normal mutex_unlock in this call.
328 * This should never happen, always use ww_mutex_unlock.
330 DEBUG_LOCKS_WARN_ON(ww->ctx);
333 * Not quite done after calling ww_acquire_done() ?
335 DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
337 if (ww_ctx->contending_lock) {
339 * After -EDEADLK you tried to
340 * acquire a different ww_mutex? Bad!
342 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
345 * You called ww_mutex_lock after receiving -EDEADLK,
346 * but 'forgot' to unlock everything else first?
348 DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
349 ww_ctx->contending_lock = NULL;
353 * Naughty, using a different class will lead to undefined behavior!
355 DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
361 * after acquiring lock with fastpath or when we lost out in contested
362 * slowpath, set ctx and wake up any waiters so they can recheck.
364 * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
365 * as the fastpath and opportunistic spinning are disabled in that case.
367 static __always_inline void
368 ww_mutex_set_context_fastpath(struct ww_mutex *lock,
369 struct ww_acquire_ctx *ctx)
372 struct mutex_waiter *cur;
374 ww_mutex_lock_acquired(lock, ctx);
379 * The lock->ctx update should be visible on all cores before
380 * the atomic read is done, otherwise contended waiters might be
381 * missed. The contended waiters will either see ww_ctx == NULL
382 * and keep spinning, or it will acquire wait_lock, add itself
383 * to waiter list and sleep.
388 * Check if lock is contended, if not there is nobody to wake up
390 if (likely(atomic_read(&lock->base.count) == 0))
394 * Uh oh, we raced in fastpath, wake up everyone in this case,
395 * so they can see the new lock->ctx.
397 spin_lock_mutex(&lock->base.wait_lock, flags);
398 list_for_each_entry(cur, &lock->base.wait_list, list) {
399 debug_mutex_wake_waiter(&lock->base, cur);
400 wake_up_process(cur->task);
402 spin_unlock_mutex(&lock->base.wait_lock, flags);
406 * Lock a mutex (possibly interruptible), slowpath:
408 static __always_inline int __sched
409 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
410 struct lockdep_map *nest_lock, unsigned long ip,
411 struct ww_acquire_ctx *ww_ctx)
413 struct task_struct *task = current;
414 struct mutex_waiter waiter;
419 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
421 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
423 * Optimistic spinning.
425 * We try to spin for acquisition when we find that there are no
426 * pending waiters and the lock owner is currently running on a
429 * The rationale is that if the lock owner is running, it is likely to
430 * release the lock soon.
432 * Since this needs the lock owner, and this mutex implementation
433 * doesn't track the owner atomically in the lock field, we need to
434 * track it non-atomically.
436 * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
437 * to serialize everything.
439 * The mutex spinners are queued up using MCS lock so that only one
440 * spinner can compete for the mutex. However, if mutex spinning isn't
441 * going to happen, there is no point in going through the lock/unlock
444 if (!mutex_can_spin_on_owner(lock))
448 struct task_struct *owner;
449 struct mspin_node node;
451 if (!__builtin_constant_p(ww_ctx == NULL) && ww_ctx->acquired > 0) {
454 ww = container_of(lock, struct ww_mutex, base);
456 * If ww->ctx is set the contents are undefined, only
457 * by acquiring wait_lock there is a guarantee that
458 * they are not invalid when reading.
460 * As such, when deadlock detection needs to be
461 * performed the optimistic spinning cannot be done.
463 if (ACCESS_ONCE(ww->ctx))
468 * If there's an owner, wait for it to either
469 * release the lock or go to sleep.
471 mspin_lock(MLOCK(lock), &node);
472 owner = ACCESS_ONCE(lock->owner);
473 if (owner && !mutex_spin_on_owner(lock, owner)) {
474 mspin_unlock(MLOCK(lock), &node);
478 if ((atomic_read(&lock->count) == 1) &&
479 (atomic_cmpxchg(&lock->count, 1, 0) == 1)) {
480 lock_acquired(&lock->dep_map, ip);
481 if (!__builtin_constant_p(ww_ctx == NULL)) {
483 ww = container_of(lock, struct ww_mutex, base);
485 ww_mutex_set_context_fastpath(ww, ww_ctx);
488 mutex_set_owner(lock);
489 mspin_unlock(MLOCK(lock), &node);
493 mspin_unlock(MLOCK(lock), &node);
496 * When there's no owner, we might have preempted between the
497 * owner acquiring the lock and setting the owner field. If
498 * we're an RT task that will live-lock because we won't let
499 * the owner complete.
501 if (!owner && (need_resched() || rt_task(task)))
505 * The cpu_relax() call is a compiler barrier which forces
506 * everything in this loop to be re-loaded. We don't need
507 * memory barriers as we'll eventually observe the right
508 * values at the cost of a few extra spins.
510 arch_mutex_cpu_relax();
514 spin_lock_mutex(&lock->wait_lock, flags);
516 debug_mutex_lock_common(lock, &waiter);
517 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
519 /* add waiting tasks to the end of the waitqueue (FIFO): */
520 list_add_tail(&waiter.list, &lock->wait_list);
523 if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, -1) == 1))
526 lock_contended(&lock->dep_map, ip);
530 * Lets try to take the lock again - this is needed even if
531 * we get here for the first time (shortly after failing to
532 * acquire the lock), to make sure that we get a wakeup once
533 * it's unlocked. Later on, if we sleep, this is the
534 * operation that gives us the lock. We xchg it to -1, so
535 * that when we release the lock, we properly wake up the
538 if (MUTEX_SHOW_NO_WAITER(lock) &&
539 (atomic_xchg(&lock->count, -1) == 1))
543 * got a signal? (This code gets eliminated in the
544 * TASK_UNINTERRUPTIBLE case.)
546 if (unlikely(signal_pending_state(state, task))) {
551 if (!__builtin_constant_p(ww_ctx == NULL) && ww_ctx->acquired > 0) {
552 ret = __mutex_lock_check_stamp(lock, ww_ctx);
557 __set_task_state(task, state);
559 /* didn't get the lock, go to sleep: */
560 spin_unlock_mutex(&lock->wait_lock, flags);
561 schedule_preempt_disabled();
562 spin_lock_mutex(&lock->wait_lock, flags);
566 lock_acquired(&lock->dep_map, ip);
567 /* got the lock - rejoice! */
568 mutex_remove_waiter(lock, &waiter, current_thread_info());
569 mutex_set_owner(lock);
571 if (!__builtin_constant_p(ww_ctx == NULL)) {
572 struct ww_mutex *ww = container_of(lock,
575 struct mutex_waiter *cur;
578 * This branch gets optimized out for the common case,
579 * and is only important for ww_mutex_lock.
582 ww_mutex_lock_acquired(ww, ww_ctx);
586 * Give any possible sleeping processes the chance to wake up,
587 * so they can recheck if they have to back off.
589 list_for_each_entry(cur, &lock->wait_list, list) {
590 debug_mutex_wake_waiter(lock, cur);
591 wake_up_process(cur->task);
595 /* set it to 0 if there are no waiters left: */
596 if (likely(list_empty(&lock->wait_list)))
597 atomic_set(&lock->count, 0);
599 spin_unlock_mutex(&lock->wait_lock, flags);
601 debug_mutex_free_waiter(&waiter);
607 mutex_remove_waiter(lock, &waiter, task_thread_info(task));
608 spin_unlock_mutex(&lock->wait_lock, flags);
609 debug_mutex_free_waiter(&waiter);
610 mutex_release(&lock->dep_map, 1, ip);
615 #ifdef CONFIG_DEBUG_LOCK_ALLOC
617 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
620 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
621 subclass, NULL, _RET_IP_, NULL);
624 EXPORT_SYMBOL_GPL(mutex_lock_nested);
627 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
630 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
631 0, nest, _RET_IP_, NULL);
634 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
637 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
640 return __mutex_lock_common(lock, TASK_KILLABLE,
641 subclass, NULL, _RET_IP_, NULL);
643 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
646 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
649 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
650 subclass, NULL, _RET_IP_, NULL);
653 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
656 ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
658 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
661 if (ctx->deadlock_inject_countdown-- == 0) {
662 tmp = ctx->deadlock_inject_interval;
663 if (tmp > UINT_MAX/4)
666 tmp = tmp*2 + tmp + tmp/2;
668 ctx->deadlock_inject_interval = tmp;
669 ctx->deadlock_inject_countdown = tmp;
670 ctx->contending_lock = lock;
672 ww_mutex_unlock(lock);
682 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
687 ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
688 0, &ctx->dep_map, _RET_IP_, ctx);
689 if (!ret && ctx->acquired > 1)
690 return ww_mutex_deadlock_injection(lock, ctx);
694 EXPORT_SYMBOL_GPL(__ww_mutex_lock);
697 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
702 ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
703 0, &ctx->dep_map, _RET_IP_, ctx);
705 if (!ret && ctx->acquired > 1)
706 return ww_mutex_deadlock_injection(lock, ctx);
710 EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
715 * Release the lock, slowpath:
718 __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
720 struct mutex *lock = container_of(lock_count, struct mutex, count);
723 spin_lock_mutex(&lock->wait_lock, flags);
724 mutex_release(&lock->dep_map, nested, _RET_IP_);
725 debug_mutex_unlock(lock);
728 * some architectures leave the lock unlocked in the fastpath failure
729 * case, others need to leave it locked. In the later case we have to
732 if (__mutex_slowpath_needs_to_unlock())
733 atomic_set(&lock->count, 1);
735 if (!list_empty(&lock->wait_list)) {
736 /* get the first entry from the wait-list: */
737 struct mutex_waiter *waiter =
738 list_entry(lock->wait_list.next,
739 struct mutex_waiter, list);
741 debug_mutex_wake_waiter(lock, waiter);
743 wake_up_process(waiter->task);
746 spin_unlock_mutex(&lock->wait_lock, flags);
750 * Release the lock, slowpath:
752 static __used noinline void
753 __mutex_unlock_slowpath(atomic_t *lock_count)
755 __mutex_unlock_common_slowpath(lock_count, 1);
758 #ifndef CONFIG_DEBUG_LOCK_ALLOC
760 * Here come the less common (and hence less performance-critical) APIs:
761 * mutex_lock_interruptible() and mutex_trylock().
763 static noinline int __sched
764 __mutex_lock_killable_slowpath(struct mutex *lock);
766 static noinline int __sched
767 __mutex_lock_interruptible_slowpath(struct mutex *lock);
770 * mutex_lock_interruptible - acquire the mutex, interruptible
771 * @lock: the mutex to be acquired
773 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
774 * been acquired or sleep until the mutex becomes available. If a
775 * signal arrives while waiting for the lock then this function
778 * This function is similar to (but not equivalent to) down_interruptible().
780 int __sched mutex_lock_interruptible(struct mutex *lock)
785 ret = __mutex_fastpath_lock_retval(&lock->count);
787 mutex_set_owner(lock);
790 return __mutex_lock_interruptible_slowpath(lock);
793 EXPORT_SYMBOL(mutex_lock_interruptible);
795 int __sched mutex_lock_killable(struct mutex *lock)
800 ret = __mutex_fastpath_lock_retval(&lock->count);
802 mutex_set_owner(lock);
805 return __mutex_lock_killable_slowpath(lock);
807 EXPORT_SYMBOL(mutex_lock_killable);
809 static __used noinline void __sched
810 __mutex_lock_slowpath(atomic_t *lock_count)
812 struct mutex *lock = container_of(lock_count, struct mutex, count);
814 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
815 NULL, _RET_IP_, NULL);
818 static noinline int __sched
819 __mutex_lock_killable_slowpath(struct mutex *lock)
821 return __mutex_lock_common(lock, TASK_KILLABLE, 0,
822 NULL, _RET_IP_, NULL);
825 static noinline int __sched
826 __mutex_lock_interruptible_slowpath(struct mutex *lock)
828 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
829 NULL, _RET_IP_, NULL);
832 static noinline int __sched
833 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
835 return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
836 NULL, _RET_IP_, ctx);
839 static noinline int __sched
840 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
841 struct ww_acquire_ctx *ctx)
843 return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
844 NULL, _RET_IP_, ctx);
850 * Spinlock based trylock, we take the spinlock and check whether we
853 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
855 struct mutex *lock = container_of(lock_count, struct mutex, count);
859 spin_lock_mutex(&lock->wait_lock, flags);
861 prev = atomic_xchg(&lock->count, -1);
862 if (likely(prev == 1)) {
863 mutex_set_owner(lock);
864 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
867 /* Set it back to 0 if there are no waiters: */
868 if (likely(list_empty(&lock->wait_list)))
869 atomic_set(&lock->count, 0);
871 spin_unlock_mutex(&lock->wait_lock, flags);
877 * mutex_trylock - try to acquire the mutex, without waiting
878 * @lock: the mutex to be acquired
880 * Try to acquire the mutex atomically. Returns 1 if the mutex
881 * has been acquired successfully, and 0 on contention.
883 * NOTE: this function follows the spin_trylock() convention, so
884 * it is negated from the down_trylock() return values! Be careful
885 * about this when converting semaphore users to mutexes.
887 * This function must not be used in interrupt context. The
888 * mutex must be released by the same task that acquired it.
890 int __sched mutex_trylock(struct mutex *lock)
894 ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
896 mutex_set_owner(lock);
900 EXPORT_SYMBOL(mutex_trylock);
902 #ifndef CONFIG_DEBUG_LOCK_ALLOC
904 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
910 ret = __mutex_fastpath_lock_retval(&lock->base.count);
913 ww_mutex_set_context_fastpath(lock, ctx);
914 mutex_set_owner(&lock->base);
916 ret = __ww_mutex_lock_slowpath(lock, ctx);
919 EXPORT_SYMBOL(__ww_mutex_lock);
922 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
928 ret = __mutex_fastpath_lock_retval(&lock->base.count);
931 ww_mutex_set_context_fastpath(lock, ctx);
932 mutex_set_owner(&lock->base);
934 ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx);
937 EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
942 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
943 * @cnt: the atomic which we are to dec
944 * @lock: the mutex to return holding if we dec to 0
946 * return true and hold lock if we dec to 0, return false otherwise
948 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
950 /* dec if we can't possibly hit 0 */
951 if (atomic_add_unless(cnt, -1, 1))
953 /* we might hit 0, so take the lock */
955 if (!atomic_dec_and_test(cnt)) {
956 /* when we actually did the dec, we didn't hit 0 */
960 /* we hit 0, and we hold the lock */
963 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);