2 * kernel/locking/mutex.c
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/locking/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>
28 #include <linux/osq_lock.h>
30 #ifdef CONFIG_DEBUG_MUTEXES
31 # include "mutex-debug.h"
37 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
39 atomic_long_set(&lock->owner, 0);
40 spin_lock_init(&lock->wait_lock);
41 INIT_LIST_HEAD(&lock->wait_list);
42 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
43 osq_lock_init(&lock->osq);
46 debug_mutex_init(lock, name, key);
48 EXPORT_SYMBOL(__mutex_init);
51 * @owner: contains: 'struct task_struct *' to the current lock owner,
52 * NULL means not owned. Since task_struct pointers are aligned at
53 * at least L1_CACHE_BYTES, we have low bits to store extra state.
55 * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
56 * Bit1 indicates unlock needs to hand the lock to the top-waiter
57 * Bit2 indicates handoff has been done and we're waiting for pickup.
59 #define MUTEX_FLAG_WAITERS 0x01
60 #define MUTEX_FLAG_HANDOFF 0x02
61 #define MUTEX_FLAG_PICKUP 0x04
63 #define MUTEX_FLAGS 0x07
65 static inline struct task_struct *__owner_task(unsigned long owner)
67 return (struct task_struct *)(owner & ~MUTEX_FLAGS);
70 static inline unsigned long __owner_flags(unsigned long owner)
72 return owner & MUTEX_FLAGS;
76 * Trylock variant that retuns the owning task on failure.
78 static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
80 unsigned long owner, curr = (unsigned long)current;
82 owner = atomic_long_read(&lock->owner);
83 for (;;) { /* must loop, can race against a flag */
84 unsigned long old, flags = __owner_flags(owner);
85 unsigned long task = owner & ~MUTEX_FLAGS;
88 if (likely(task != curr))
91 if (likely(!(flags & MUTEX_FLAG_PICKUP)))
94 flags &= ~MUTEX_FLAG_PICKUP;
96 #ifdef CONFIG_DEBUG_MUTEXES
97 DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
102 * We set the HANDOFF bit, we must make sure it doesn't live
103 * past the point where we acquire it. This would be possible
104 * if we (accidentally) set the bit on an unlocked mutex.
106 flags &= ~MUTEX_FLAG_HANDOFF;
108 old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
115 return __owner_task(owner);
119 * Actual trylock that will work on any unlocked state.
121 static inline bool __mutex_trylock(struct mutex *lock)
123 return !__mutex_trylock_or_owner(lock);
126 #ifndef CONFIG_DEBUG_LOCK_ALLOC
128 * Lockdep annotations are contained to the slow paths for simplicity.
129 * There is nothing that would stop spreading the lockdep annotations outwards
134 * Optimistic trylock that only works in the uncontended case. Make sure to
135 * follow with a __mutex_trylock() before failing.
137 static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
139 unsigned long curr = (unsigned long)current;
141 if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr))
147 static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
149 unsigned long curr = (unsigned long)current;
151 if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
158 static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
160 atomic_long_or(flag, &lock->owner);
163 static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
165 atomic_long_andnot(flag, &lock->owner);
168 static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
170 return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
174 * Give up ownership to a specific task, when @task = NULL, this is equivalent
175 * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
176 * WAITERS. Provides RELEASE semantics like a regular unlock, the
177 * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
179 static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
181 unsigned long owner = atomic_long_read(&lock->owner);
184 unsigned long old, new;
186 #ifdef CONFIG_DEBUG_MUTEXES
187 DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
188 DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
191 new = (owner & MUTEX_FLAG_WAITERS);
192 new |= (unsigned long)task;
194 new |= MUTEX_FLAG_PICKUP;
196 old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
204 #ifndef CONFIG_DEBUG_LOCK_ALLOC
206 * We split the mutex lock/unlock logic into separate fastpath and
207 * slowpath functions, to reduce the register pressure on the fastpath.
208 * We also put the fastpath first in the kernel image, to make sure the
209 * branch is predicted by the CPU as default-untaken.
211 static void __sched __mutex_lock_slowpath(struct mutex *lock);
214 * mutex_lock - acquire the mutex
215 * @lock: the mutex to be acquired
217 * Lock the mutex exclusively for this task. If the mutex is not
218 * available right now, it will sleep until it can get it.
220 * The mutex must later on be released by the same task that
221 * acquired it. Recursive locking is not allowed. The task
222 * may not exit without first unlocking the mutex. Also, kernel
223 * memory where the mutex resides must not be freed with
224 * the mutex still locked. The mutex must first be initialized
225 * (or statically defined) before it can be locked. memset()-ing
226 * the mutex to 0 is not allowed.
228 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
229 * checks that will enforce the restrictions and will also do
230 * deadlock debugging. )
232 * This function is similar to (but not equivalent to) down().
234 void __sched mutex_lock(struct mutex *lock)
238 if (!__mutex_trylock_fast(lock))
239 __mutex_lock_slowpath(lock);
241 EXPORT_SYMBOL(mutex_lock);
244 static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
245 struct ww_acquire_ctx *ww_ctx)
247 #ifdef CONFIG_DEBUG_MUTEXES
249 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
250 * but released with a normal mutex_unlock in this call.
252 * This should never happen, always use ww_mutex_unlock.
254 DEBUG_LOCKS_WARN_ON(ww->ctx);
257 * Not quite done after calling ww_acquire_done() ?
259 DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
261 if (ww_ctx->contending_lock) {
263 * After -EDEADLK you tried to
264 * acquire a different ww_mutex? Bad!
266 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
269 * You called ww_mutex_lock after receiving -EDEADLK,
270 * but 'forgot' to unlock everything else first?
272 DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
273 ww_ctx->contending_lock = NULL;
277 * Naughty, using a different class will lead to undefined behavior!
279 DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
284 static inline bool __sched
285 __ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
287 return a->stamp - b->stamp <= LONG_MAX &&
288 (a->stamp != b->stamp || a > b);
292 * After acquiring lock with fastpath or when we lost out in contested
293 * slowpath, set ctx and wake up any waiters so they can recheck.
295 static __always_inline void
296 ww_mutex_set_context_fastpath(struct ww_mutex *lock,
297 struct ww_acquire_ctx *ctx)
300 struct mutex_waiter *cur;
302 ww_mutex_lock_acquired(lock, ctx);
307 * The lock->ctx update should be visible on all cores before
308 * the atomic read is done, otherwise contended waiters might be
309 * missed. The contended waiters will either see ww_ctx == NULL
310 * and keep spinning, or it will acquire wait_lock, add itself
311 * to waiter list and sleep.
316 * Check if lock is contended, if not there is nobody to wake up
318 if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
322 * Uh oh, we raced in fastpath, wake up everyone in this case,
323 * so they can see the new lock->ctx.
325 spin_lock_mutex(&lock->base.wait_lock, flags);
326 list_for_each_entry(cur, &lock->base.wait_list, list) {
327 debug_mutex_wake_waiter(&lock->base, cur);
328 wake_up_process(cur->task);
330 spin_unlock_mutex(&lock->base.wait_lock, flags);
334 * After acquiring lock in the slowpath set ctx and wake up any
335 * waiters so they can recheck.
337 * Callers must hold the mutex wait_lock.
339 static __always_inline void
340 ww_mutex_set_context_slowpath(struct ww_mutex *lock,
341 struct ww_acquire_ctx *ctx)
343 struct mutex_waiter *cur;
345 ww_mutex_lock_acquired(lock, ctx);
349 * Give any possible sleeping processes the chance to wake up,
350 * so they can recheck if they have to back off.
352 list_for_each_entry(cur, &lock->base.wait_list, list) {
353 debug_mutex_wake_waiter(&lock->base, cur);
354 wake_up_process(cur->task);
358 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
360 * Look out! "owner" is an entirely speculative pointer
361 * access and not reliable.
364 bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
369 while (__mutex_owner(lock) == owner) {
371 * Ensure we emit the owner->on_cpu, dereference _after_
372 * checking lock->owner still matches owner. If that fails,
373 * owner might point to freed memory. If it still matches,
374 * the rcu_read_lock() ensures the memory stays valid.
379 * Use vcpu_is_preempted to detect lock holder preemption issue.
381 if (!owner->on_cpu || need_resched() ||
382 vcpu_is_preempted(task_cpu(owner))) {
395 * Initial check for entering the mutex spinning loop
397 static inline int mutex_can_spin_on_owner(struct mutex *lock)
399 struct task_struct *owner;
406 owner = __mutex_owner(lock);
409 * As lock holder preemption issue, we both skip spinning if task is not
410 * on cpu or its cpu is preempted
413 retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
417 * If lock->owner is not set, the mutex has been released. Return true
418 * such that we'll trylock in the spin path, which is a faster option
419 * than the blocking slow path.
425 * Optimistic spinning.
427 * We try to spin for acquisition when we find that the lock owner
428 * is currently running on a (different) CPU and while we don't
429 * need to reschedule. The rationale is that if the lock owner is
430 * running, it is likely to release the lock soon.
432 * The mutex spinners are queued up using MCS lock so that only one
433 * spinner can compete for the mutex. However, if mutex spinning isn't
434 * going to happen, there is no point in going through the lock/unlock
437 * Returns true when the lock was taken, otherwise false, indicating
438 * that we need to jump to the slowpath and sleep.
440 * The waiter flag is set to true if the spinner is a waiter in the wait
441 * queue. The waiter-spinner will spin on the lock directly and concurrently
442 * with the spinner at the head of the OSQ, if present, until the owner is
445 static bool mutex_optimistic_spin(struct mutex *lock,
446 struct ww_acquire_ctx *ww_ctx,
447 const bool use_ww_ctx, const bool waiter)
451 * The purpose of the mutex_can_spin_on_owner() function is
452 * to eliminate the overhead of osq_lock() and osq_unlock()
453 * in case spinning isn't possible. As a waiter-spinner
454 * is not going to take OSQ lock anyway, there is no need
455 * to call mutex_can_spin_on_owner().
457 if (!mutex_can_spin_on_owner(lock))
461 * In order to avoid a stampede of mutex spinners trying to
462 * acquire the mutex all at once, the spinners need to take a
463 * MCS (queued) lock first before spinning on the owner field.
465 if (!osq_lock(&lock->osq))
470 struct task_struct *owner;
472 if (use_ww_ctx && ww_ctx->acquired > 0) {
475 ww = container_of(lock, struct ww_mutex, base);
477 * If ww->ctx is set the contents are undefined, only
478 * by acquiring wait_lock there is a guarantee that
479 * they are not invalid when reading.
481 * As such, when deadlock detection needs to be
482 * performed the optimistic spinning cannot be done.
484 if (READ_ONCE(ww->ctx))
488 /* Try to acquire the mutex... */
489 owner = __mutex_trylock_or_owner(lock);
494 * There's an owner, wait for it to either
495 * release the lock or go to sleep.
497 if (!mutex_spin_on_owner(lock, owner))
501 * The cpu_relax() call is a compiler barrier which forces
502 * everything in this loop to be re-loaded. We don't need
503 * memory barriers as we'll eventually observe the right
504 * values at the cost of a few extra spins.
510 osq_unlock(&lock->osq);
517 osq_unlock(&lock->osq);
521 * If we fell out of the spin path because of need_resched(),
522 * reschedule now, before we try-lock the mutex. This avoids getting
523 * scheduled out right after we obtained the mutex.
525 if (need_resched()) {
527 * We _should_ have TASK_RUNNING here, but just in case
528 * we do not, make it so, otherwise we might get stuck.
530 __set_current_state(TASK_RUNNING);
531 schedule_preempt_disabled();
537 static bool mutex_optimistic_spin(struct mutex *lock,
538 struct ww_acquire_ctx *ww_ctx,
539 const bool use_ww_ctx, const bool waiter)
545 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
548 * mutex_unlock - release the mutex
549 * @lock: the mutex to be released
551 * Unlock a mutex that has been locked by this task previously.
553 * This function must not be used in interrupt context. Unlocking
554 * of a not locked mutex is not allowed.
556 * This function is similar to (but not equivalent to) up().
558 void __sched mutex_unlock(struct mutex *lock)
560 #ifndef CONFIG_DEBUG_LOCK_ALLOC
561 if (__mutex_unlock_fast(lock))
564 __mutex_unlock_slowpath(lock, _RET_IP_);
566 EXPORT_SYMBOL(mutex_unlock);
569 * ww_mutex_unlock - release the w/w mutex
570 * @lock: the mutex to be released
572 * Unlock a mutex that has been locked by this task previously with any of the
573 * ww_mutex_lock* functions (with or without an acquire context). It is
574 * forbidden to release the locks after releasing the acquire context.
576 * This function must not be used in interrupt context. Unlocking
577 * of a unlocked mutex is not allowed.
579 void __sched ww_mutex_unlock(struct ww_mutex *lock)
582 * The unlocking fastpath is the 0->1 transition from 'locked'
583 * into 'unlocked' state:
586 #ifdef CONFIG_DEBUG_MUTEXES
587 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
589 if (lock->ctx->acquired > 0)
590 lock->ctx->acquired--;
594 mutex_unlock(&lock->base);
596 EXPORT_SYMBOL(ww_mutex_unlock);
598 static inline int __sched
599 __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
601 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
602 struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
607 if (__ww_ctx_stamp_after(ctx, hold_ctx)) {
608 #ifdef CONFIG_DEBUG_MUTEXES
609 DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
610 ctx->contending_lock = ww;
619 * Lock a mutex (possibly interruptible), slowpath:
621 static __always_inline int __sched
622 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
623 struct lockdep_map *nest_lock, unsigned long ip,
624 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
626 struct mutex_waiter waiter;
633 ww = container_of(lock, struct ww_mutex, base);
634 if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
639 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
641 if (__mutex_trylock(lock) ||
642 mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) {
643 /* got the lock, yay! */
644 lock_acquired(&lock->dep_map, ip);
646 ww_mutex_set_context_fastpath(ww, ww_ctx);
651 spin_lock_mutex(&lock->wait_lock, flags);
653 * After waiting to acquire the wait_lock, try again.
655 if (__mutex_trylock(lock))
658 debug_mutex_lock_common(lock, &waiter);
659 debug_mutex_add_waiter(lock, &waiter, current);
661 /* add waiting tasks to the end of the waitqueue (FIFO): */
662 list_add_tail(&waiter.list, &lock->wait_list);
663 waiter.task = current;
665 if (__mutex_waiter_is_first(lock, &waiter))
666 __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
668 lock_contended(&lock->dep_map, ip);
670 set_current_state(state);
673 * Once we hold wait_lock, we're serialized against
674 * mutex_unlock() handing the lock off to us, do a trylock
675 * before testing the error conditions to make sure we pick up
678 if (__mutex_trylock(lock))
682 * Check for signals and wound conditions while holding
683 * wait_lock. This ensures the lock cancellation is ordered
684 * against mutex_unlock() and wake-ups do not go missing.
686 if (unlikely(signal_pending_state(state, current))) {
691 if (use_ww_ctx && ww_ctx->acquired > 0) {
692 ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);
697 spin_unlock_mutex(&lock->wait_lock, flags);
698 schedule_preempt_disabled();
700 if (!first && __mutex_waiter_is_first(lock, &waiter)) {
702 __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
705 set_current_state(state);
707 * Here we order against unlock; we must either see it change
708 * state back to RUNNING and fall through the next schedule(),
709 * or we must see its unlock and acquire.
711 if (__mutex_trylock(lock) ||
712 (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, true)))
715 spin_lock_mutex(&lock->wait_lock, flags);
717 spin_lock_mutex(&lock->wait_lock, flags);
719 __set_current_state(TASK_RUNNING);
721 mutex_remove_waiter(lock, &waiter, current);
722 if (likely(list_empty(&lock->wait_list)))
723 __mutex_clear_flag(lock, MUTEX_FLAGS);
725 debug_mutex_free_waiter(&waiter);
728 /* got the lock - cleanup and rejoice! */
729 lock_acquired(&lock->dep_map, ip);
732 ww_mutex_set_context_slowpath(ww, ww_ctx);
734 spin_unlock_mutex(&lock->wait_lock, flags);
739 __set_current_state(TASK_RUNNING);
740 mutex_remove_waiter(lock, &waiter, current);
741 spin_unlock_mutex(&lock->wait_lock, flags);
742 debug_mutex_free_waiter(&waiter);
743 mutex_release(&lock->dep_map, 1, ip);
748 #ifdef CONFIG_DEBUG_LOCK_ALLOC
750 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
753 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
754 subclass, NULL, _RET_IP_, NULL, 0);
757 EXPORT_SYMBOL_GPL(mutex_lock_nested);
760 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
763 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
764 0, nest, _RET_IP_, NULL, 0);
766 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
769 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
772 return __mutex_lock_common(lock, TASK_KILLABLE,
773 subclass, NULL, _RET_IP_, NULL, 0);
775 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
778 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
781 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
782 subclass, NULL, _RET_IP_, NULL, 0);
784 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
787 ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
789 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
792 if (ctx->deadlock_inject_countdown-- == 0) {
793 tmp = ctx->deadlock_inject_interval;
794 if (tmp > UINT_MAX/4)
797 tmp = tmp*2 + tmp + tmp/2;
799 ctx->deadlock_inject_interval = tmp;
800 ctx->deadlock_inject_countdown = tmp;
801 ctx->contending_lock = lock;
803 ww_mutex_unlock(lock);
813 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
818 ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
819 0, &ctx->dep_map, _RET_IP_, ctx, 1);
820 if (!ret && ctx->acquired > 1)
821 return ww_mutex_deadlock_injection(lock, ctx);
825 EXPORT_SYMBOL_GPL(__ww_mutex_lock);
828 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
833 ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
834 0, &ctx->dep_map, _RET_IP_, ctx, 1);
836 if (!ret && ctx->acquired > 1)
837 return ww_mutex_deadlock_injection(lock, ctx);
841 EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
846 * Release the lock, slowpath:
848 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
850 struct task_struct *next = NULL;
851 unsigned long owner, flags;
852 DEFINE_WAKE_Q(wake_q);
854 mutex_release(&lock->dep_map, 1, ip);
857 * Release the lock before (potentially) taking the spinlock such that
858 * other contenders can get on with things ASAP.
860 * Except when HANDOFF, in that case we must not clear the owner field,
861 * but instead set it to the top waiter.
863 owner = atomic_long_read(&lock->owner);
867 #ifdef CONFIG_DEBUG_MUTEXES
868 DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
869 DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
872 if (owner & MUTEX_FLAG_HANDOFF)
875 old = atomic_long_cmpxchg_release(&lock->owner, owner,
876 __owner_flags(owner));
878 if (owner & MUTEX_FLAG_WAITERS)
887 spin_lock_mutex(&lock->wait_lock, flags);
888 debug_mutex_unlock(lock);
889 if (!list_empty(&lock->wait_list)) {
890 /* get the first entry from the wait-list: */
891 struct mutex_waiter *waiter =
892 list_first_entry(&lock->wait_list,
893 struct mutex_waiter, list);
897 debug_mutex_wake_waiter(lock, waiter);
898 wake_q_add(&wake_q, next);
901 if (owner & MUTEX_FLAG_HANDOFF)
902 __mutex_handoff(lock, next);
904 spin_unlock_mutex(&lock->wait_lock, flags);
909 #ifndef CONFIG_DEBUG_LOCK_ALLOC
911 * Here come the less common (and hence less performance-critical) APIs:
912 * mutex_lock_interruptible() and mutex_trylock().
914 static noinline int __sched
915 __mutex_lock_killable_slowpath(struct mutex *lock);
917 static noinline int __sched
918 __mutex_lock_interruptible_slowpath(struct mutex *lock);
921 * mutex_lock_interruptible - acquire the mutex, interruptible
922 * @lock: the mutex to be acquired
924 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
925 * been acquired or sleep until the mutex becomes available. If a
926 * signal arrives while waiting for the lock then this function
929 * This function is similar to (but not equivalent to) down_interruptible().
931 int __sched mutex_lock_interruptible(struct mutex *lock)
935 if (__mutex_trylock_fast(lock))
938 return __mutex_lock_interruptible_slowpath(lock);
941 EXPORT_SYMBOL(mutex_lock_interruptible);
943 int __sched mutex_lock_killable(struct mutex *lock)
947 if (__mutex_trylock_fast(lock))
950 return __mutex_lock_killable_slowpath(lock);
952 EXPORT_SYMBOL(mutex_lock_killable);
954 static noinline void __sched
955 __mutex_lock_slowpath(struct mutex *lock)
957 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
958 NULL, _RET_IP_, NULL, 0);
961 static noinline int __sched
962 __mutex_lock_killable_slowpath(struct mutex *lock)
964 return __mutex_lock_common(lock, TASK_KILLABLE, 0,
965 NULL, _RET_IP_, NULL, 0);
968 static noinline int __sched
969 __mutex_lock_interruptible_slowpath(struct mutex *lock)
971 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
972 NULL, _RET_IP_, NULL, 0);
975 static noinline int __sched
976 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
978 return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
979 NULL, _RET_IP_, ctx, 1);
982 static noinline int __sched
983 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
984 struct ww_acquire_ctx *ctx)
986 return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
987 NULL, _RET_IP_, ctx, 1);
993 * mutex_trylock - try to acquire the mutex, without waiting
994 * @lock: the mutex to be acquired
996 * Try to acquire the mutex atomically. Returns 1 if the mutex
997 * has been acquired successfully, and 0 on contention.
999 * NOTE: this function follows the spin_trylock() convention, so
1000 * it is negated from the down_trylock() return values! Be careful
1001 * about this when converting semaphore users to mutexes.
1003 * This function must not be used in interrupt context. The
1004 * mutex must be released by the same task that acquired it.
1006 int __sched mutex_trylock(struct mutex *lock)
1008 bool locked = __mutex_trylock(lock);
1011 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1015 EXPORT_SYMBOL(mutex_trylock);
1017 #ifndef CONFIG_DEBUG_LOCK_ALLOC
1019 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1023 if (__mutex_trylock_fast(&lock->base)) {
1024 ww_mutex_set_context_fastpath(lock, ctx);
1028 return __ww_mutex_lock_slowpath(lock, ctx);
1030 EXPORT_SYMBOL(__ww_mutex_lock);
1033 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1037 if (__mutex_trylock_fast(&lock->base)) {
1038 ww_mutex_set_context_fastpath(lock, ctx);
1042 return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1044 EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
1049 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1050 * @cnt: the atomic which we are to dec
1051 * @lock: the mutex to return holding if we dec to 0
1053 * return true and hold lock if we dec to 0, return false otherwise
1055 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1057 /* dec if we can't possibly hit 0 */
1058 if (atomic_add_unless(cnt, -1, 1))
1060 /* we might hit 0, so take the lock */
1062 if (!atomic_dec_and_test(cnt)) {
1063 /* when we actually did the dec, we didn't hit 0 */
1067 /* we hit 0, and we hold the lock */
1070 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);