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
245 ww_mutex_lock_acquired(struct ww_mutex *ww, 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 * Wake up any waiters that may have to back off when the lock is held by the
295 * Due to the invariants on the wait list, this can only affect the first
296 * waiter with a context.
298 * The current task must not be on the wait list.
301 __ww_mutex_wakeup_for_backoff(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
303 struct mutex_waiter *cur;
305 lockdep_assert_held(&lock->wait_lock);
307 list_for_each_entry(cur, &lock->wait_list, list) {
311 if (cur->ww_ctx->acquired > 0 &&
312 __ww_ctx_stamp_after(cur->ww_ctx, ww_ctx)) {
313 debug_mutex_wake_waiter(lock, cur);
314 wake_up_process(cur->task);
322 * After acquiring lock with fastpath or when we lost out in contested
323 * slowpath, set ctx and wake up any waiters so they can recheck.
325 static __always_inline void
326 ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
330 ww_mutex_lock_acquired(lock, ctx);
335 * The lock->ctx update should be visible on all cores before
336 * the atomic read is done, otherwise contended waiters might be
337 * missed. The contended waiters will either see ww_ctx == NULL
338 * and keep spinning, or it will acquire wait_lock, add itself
339 * to waiter list and sleep.
344 * Check if lock is contended, if not there is nobody to wake up
346 if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
350 * Uh oh, we raced in fastpath, wake up everyone in this case,
351 * so they can see the new lock->ctx.
353 spin_lock_mutex(&lock->base.wait_lock, flags);
354 __ww_mutex_wakeup_for_backoff(&lock->base, ctx);
355 spin_unlock_mutex(&lock->base.wait_lock, flags);
359 * After acquiring lock in the slowpath set ctx.
361 * Unlike for the fast path, the caller ensures that waiters are woken up where
364 * Callers must hold the mutex wait_lock.
366 static __always_inline void
367 ww_mutex_set_context_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
369 ww_mutex_lock_acquired(lock, ctx);
373 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
376 bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
377 struct mutex_waiter *waiter)
381 ww = container_of(lock, struct ww_mutex, base);
384 * If ww->ctx is set the contents are undefined, only
385 * by acquiring wait_lock there is a guarantee that
386 * they are not invalid when reading.
388 * As such, when deadlock detection needs to be
389 * performed the optimistic spinning cannot be done.
391 * Check this in every inner iteration because we may
392 * be racing against another thread's ww_mutex_lock.
394 if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
398 * If we aren't on the wait list yet, cancel the spin
399 * if there are waiters. We want to avoid stealing the
400 * lock from a waiter with an earlier stamp, since the
401 * other thread may already own a lock that we also
404 if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
408 * Similarly, stop spinning if we are no longer the
411 if (waiter && !__mutex_waiter_is_first(lock, waiter))
418 * Look out! "owner" is an entirely speculative pointer access and not
421 * "noinline" so that this function shows up on perf profiles.
424 bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
425 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
430 while (__mutex_owner(lock) == owner) {
432 * Ensure we emit the owner->on_cpu, dereference _after_
433 * checking lock->owner still matches owner. If that fails,
434 * owner might point to freed memory. If it still matches,
435 * the rcu_read_lock() ensures the memory stays valid.
440 * Use vcpu_is_preempted to detect lock holder preemption issue.
442 if (!owner->on_cpu || need_resched() ||
443 vcpu_is_preempted(task_cpu(owner))) {
448 if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
461 * Initial check for entering the mutex spinning loop
463 static inline int mutex_can_spin_on_owner(struct mutex *lock)
465 struct task_struct *owner;
472 owner = __mutex_owner(lock);
475 * As lock holder preemption issue, we both skip spinning if task is not
476 * on cpu or its cpu is preempted
479 retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
483 * If lock->owner is not set, the mutex has been released. Return true
484 * such that we'll trylock in the spin path, which is a faster option
485 * than the blocking slow path.
491 * Optimistic spinning.
493 * We try to spin for acquisition when we find that the lock owner
494 * is currently running on a (different) CPU and while we don't
495 * need to reschedule. The rationale is that if the lock owner is
496 * running, it is likely to release the lock soon.
498 * The mutex spinners are queued up using MCS lock so that only one
499 * spinner can compete for the mutex. However, if mutex spinning isn't
500 * going to happen, there is no point in going through the lock/unlock
503 * Returns true when the lock was taken, otherwise false, indicating
504 * that we need to jump to the slowpath and sleep.
506 * The waiter flag is set to true if the spinner is a waiter in the wait
507 * queue. The waiter-spinner will spin on the lock directly and concurrently
508 * with the spinner at the head of the OSQ, if present, until the owner is
511 static __always_inline bool
512 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
513 const bool use_ww_ctx, struct mutex_waiter *waiter)
517 * The purpose of the mutex_can_spin_on_owner() function is
518 * to eliminate the overhead of osq_lock() and osq_unlock()
519 * in case spinning isn't possible. As a waiter-spinner
520 * is not going to take OSQ lock anyway, there is no need
521 * to call mutex_can_spin_on_owner().
523 if (!mutex_can_spin_on_owner(lock))
527 * In order to avoid a stampede of mutex spinners trying to
528 * acquire the mutex all at once, the spinners need to take a
529 * MCS (queued) lock first before spinning on the owner field.
531 if (!osq_lock(&lock->osq))
536 struct task_struct *owner;
538 /* Try to acquire the mutex... */
539 owner = __mutex_trylock_or_owner(lock);
544 * There's an owner, wait for it to either
545 * release the lock or go to sleep.
547 if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
551 * The cpu_relax() call is a compiler barrier which forces
552 * everything in this loop to be re-loaded. We don't need
553 * memory barriers as we'll eventually observe the right
554 * values at the cost of a few extra spins.
560 osq_unlock(&lock->osq);
567 osq_unlock(&lock->osq);
571 * If we fell out of the spin path because of need_resched(),
572 * reschedule now, before we try-lock the mutex. This avoids getting
573 * scheduled out right after we obtained the mutex.
575 if (need_resched()) {
577 * We _should_ have TASK_RUNNING here, but just in case
578 * we do not, make it so, otherwise we might get stuck.
580 __set_current_state(TASK_RUNNING);
581 schedule_preempt_disabled();
587 static __always_inline bool
588 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
589 const bool use_ww_ctx, struct mutex_waiter *waiter)
595 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
598 * mutex_unlock - release the mutex
599 * @lock: the mutex to be released
601 * Unlock a mutex that has been locked by this task previously.
603 * This function must not be used in interrupt context. Unlocking
604 * of a not locked mutex is not allowed.
606 * This function is similar to (but not equivalent to) up().
608 void __sched mutex_unlock(struct mutex *lock)
610 #ifndef CONFIG_DEBUG_LOCK_ALLOC
611 if (__mutex_unlock_fast(lock))
614 __mutex_unlock_slowpath(lock, _RET_IP_);
616 EXPORT_SYMBOL(mutex_unlock);
619 * ww_mutex_unlock - release the w/w mutex
620 * @lock: the mutex to be released
622 * Unlock a mutex that has been locked by this task previously with any of the
623 * ww_mutex_lock* functions (with or without an acquire context). It is
624 * forbidden to release the locks after releasing the acquire context.
626 * This function must not be used in interrupt context. Unlocking
627 * of a unlocked mutex is not allowed.
629 void __sched ww_mutex_unlock(struct ww_mutex *lock)
632 * The unlocking fastpath is the 0->1 transition from 'locked'
633 * into 'unlocked' state:
636 #ifdef CONFIG_DEBUG_MUTEXES
637 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
639 if (lock->ctx->acquired > 0)
640 lock->ctx->acquired--;
644 mutex_unlock(&lock->base);
646 EXPORT_SYMBOL(ww_mutex_unlock);
648 static inline int __sched
649 __ww_mutex_lock_check_stamp(struct mutex *lock, struct mutex_waiter *waiter,
650 struct ww_acquire_ctx *ctx)
652 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
653 struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
654 struct mutex_waiter *cur;
656 if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
660 * If there is a waiter in front of us that has a context, then its
661 * stamp is earlier than ours and we must back off.
664 list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
672 #ifdef CONFIG_DEBUG_MUTEXES
673 DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
674 ctx->contending_lock = ww;
679 static inline int __sched
680 __ww_mutex_add_waiter(struct mutex_waiter *waiter,
682 struct ww_acquire_ctx *ww_ctx)
684 struct mutex_waiter *cur;
685 struct list_head *pos;
688 list_add_tail(&waiter->list, &lock->wait_list);
693 * Add the waiter before the first waiter with a higher stamp.
694 * Waiters without a context are skipped to avoid starving
697 pos = &lock->wait_list;
698 list_for_each_entry_reverse(cur, &lock->wait_list, list) {
702 if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
703 /* Back off immediately if necessary. */
704 if (ww_ctx->acquired > 0) {
705 #ifdef CONFIG_DEBUG_MUTEXES
708 ww = container_of(lock, struct ww_mutex, base);
709 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
710 ww_ctx->contending_lock = ww;
721 * Wake up the waiter so that it gets a chance to back
724 if (cur->ww_ctx->acquired > 0) {
725 debug_mutex_wake_waiter(lock, cur);
726 wake_up_process(cur->task);
730 list_add_tail(&waiter->list, pos);
735 * Lock a mutex (possibly interruptible), slowpath:
737 static __always_inline int __sched
738 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
739 struct lockdep_map *nest_lock, unsigned long ip,
740 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
742 struct mutex_waiter waiter;
750 ww = container_of(lock, struct ww_mutex, base);
751 if (use_ww_ctx && ww_ctx) {
752 if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
757 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
759 if (__mutex_trylock(lock) ||
760 mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
761 /* got the lock, yay! */
762 lock_acquired(&lock->dep_map, ip);
763 if (use_ww_ctx && ww_ctx)
764 ww_mutex_set_context_fastpath(ww, ww_ctx);
769 spin_lock_mutex(&lock->wait_lock, flags);
771 * After waiting to acquire the wait_lock, try again.
773 if (__mutex_trylock(lock)) {
774 if (use_ww_ctx && ww_ctx)
775 __ww_mutex_wakeup_for_backoff(lock, ww_ctx);
780 debug_mutex_lock_common(lock, &waiter);
781 debug_mutex_add_waiter(lock, &waiter, current);
783 lock_contended(&lock->dep_map, ip);
786 /* add waiting tasks to the end of the waitqueue (FIFO): */
787 list_add_tail(&waiter.list, &lock->wait_list);
789 /* Add in stamp order, waking up waiters that must back off. */
790 ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
792 goto err_early_backoff;
794 waiter.ww_ctx = ww_ctx;
797 waiter.task = current;
799 if (__mutex_waiter_is_first(lock, &waiter))
800 __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
802 set_current_state(state);
805 * Once we hold wait_lock, we're serialized against
806 * mutex_unlock() handing the lock off to us, do a trylock
807 * before testing the error conditions to make sure we pick up
810 if (__mutex_trylock(lock))
814 * Check for signals and wound conditions while holding
815 * wait_lock. This ensures the lock cancellation is ordered
816 * against mutex_unlock() and wake-ups do not go missing.
818 if (unlikely(signal_pending_state(state, current))) {
823 if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
824 ret = __ww_mutex_lock_check_stamp(lock, &waiter, ww_ctx);
829 spin_unlock_mutex(&lock->wait_lock, flags);
830 schedule_preempt_disabled();
833 * ww_mutex needs to always recheck its position since its waiter
834 * list is not FIFO ordered.
836 if ((use_ww_ctx && ww_ctx) || !first) {
837 first = __mutex_waiter_is_first(lock, &waiter);
839 __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
842 set_current_state(state);
844 * Here we order against unlock; we must either see it change
845 * state back to RUNNING and fall through the next schedule(),
846 * or we must see its unlock and acquire.
848 if (__mutex_trylock(lock) ||
849 (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
852 spin_lock_mutex(&lock->wait_lock, flags);
854 spin_lock_mutex(&lock->wait_lock, flags);
856 __set_current_state(TASK_RUNNING);
858 mutex_remove_waiter(lock, &waiter, current);
859 if (likely(list_empty(&lock->wait_list)))
860 __mutex_clear_flag(lock, MUTEX_FLAGS);
862 debug_mutex_free_waiter(&waiter);
865 /* got the lock - cleanup and rejoice! */
866 lock_acquired(&lock->dep_map, ip);
868 if (use_ww_ctx && ww_ctx)
869 ww_mutex_set_context_slowpath(ww, ww_ctx);
871 spin_unlock_mutex(&lock->wait_lock, flags);
876 __set_current_state(TASK_RUNNING);
877 mutex_remove_waiter(lock, &waiter, current);
879 spin_unlock_mutex(&lock->wait_lock, flags);
880 debug_mutex_free_waiter(&waiter);
881 mutex_release(&lock->dep_map, 1, ip);
887 __mutex_lock(struct mutex *lock, long state, unsigned int subclass,
888 struct lockdep_map *nest_lock, unsigned long ip)
890 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
894 __ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
895 struct lockdep_map *nest_lock, unsigned long ip,
896 struct ww_acquire_ctx *ww_ctx)
898 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
901 #ifdef CONFIG_DEBUG_LOCK_ALLOC
903 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
905 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
908 EXPORT_SYMBOL_GPL(mutex_lock_nested);
911 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
913 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
915 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
918 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
920 return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
922 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
925 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
927 return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
929 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
932 ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
934 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
937 if (ctx->deadlock_inject_countdown-- == 0) {
938 tmp = ctx->deadlock_inject_interval;
939 if (tmp > UINT_MAX/4)
942 tmp = tmp*2 + tmp + tmp/2;
944 ctx->deadlock_inject_interval = tmp;
945 ctx->deadlock_inject_countdown = tmp;
946 ctx->contending_lock = lock;
948 ww_mutex_unlock(lock);
958 ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
963 ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
964 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
966 if (!ret && ctx && ctx->acquired > 1)
967 return ww_mutex_deadlock_injection(lock, ctx);
971 EXPORT_SYMBOL_GPL(ww_mutex_lock);
974 ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
979 ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
980 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
983 if (!ret && ctx && ctx->acquired > 1)
984 return ww_mutex_deadlock_injection(lock, ctx);
988 EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
993 * Release the lock, slowpath:
995 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
997 struct task_struct *next = NULL;
998 unsigned long owner, flags;
999 DEFINE_WAKE_Q(wake_q);
1001 mutex_release(&lock->dep_map, 1, ip);
1004 * Release the lock before (potentially) taking the spinlock such that
1005 * other contenders can get on with things ASAP.
1007 * Except when HANDOFF, in that case we must not clear the owner field,
1008 * but instead set it to the top waiter.
1010 owner = atomic_long_read(&lock->owner);
1014 #ifdef CONFIG_DEBUG_MUTEXES
1015 DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
1016 DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
1019 if (owner & MUTEX_FLAG_HANDOFF)
1022 old = atomic_long_cmpxchg_release(&lock->owner, owner,
1023 __owner_flags(owner));
1025 if (owner & MUTEX_FLAG_WAITERS)
1034 spin_lock_mutex(&lock->wait_lock, flags);
1035 debug_mutex_unlock(lock);
1036 if (!list_empty(&lock->wait_list)) {
1037 /* get the first entry from the wait-list: */
1038 struct mutex_waiter *waiter =
1039 list_first_entry(&lock->wait_list,
1040 struct mutex_waiter, list);
1042 next = waiter->task;
1044 debug_mutex_wake_waiter(lock, waiter);
1045 wake_q_add(&wake_q, next);
1048 if (owner & MUTEX_FLAG_HANDOFF)
1049 __mutex_handoff(lock, next);
1051 spin_unlock_mutex(&lock->wait_lock, flags);
1056 #ifndef CONFIG_DEBUG_LOCK_ALLOC
1058 * Here come the less common (and hence less performance-critical) APIs:
1059 * mutex_lock_interruptible() and mutex_trylock().
1061 static noinline int __sched
1062 __mutex_lock_killable_slowpath(struct mutex *lock);
1064 static noinline int __sched
1065 __mutex_lock_interruptible_slowpath(struct mutex *lock);
1068 * mutex_lock_interruptible - acquire the mutex, interruptible
1069 * @lock: the mutex to be acquired
1071 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
1072 * been acquired or sleep until the mutex becomes available. If a
1073 * signal arrives while waiting for the lock then this function
1076 * This function is similar to (but not equivalent to) down_interruptible().
1078 int __sched mutex_lock_interruptible(struct mutex *lock)
1082 if (__mutex_trylock_fast(lock))
1085 return __mutex_lock_interruptible_slowpath(lock);
1088 EXPORT_SYMBOL(mutex_lock_interruptible);
1090 int __sched mutex_lock_killable(struct mutex *lock)
1094 if (__mutex_trylock_fast(lock))
1097 return __mutex_lock_killable_slowpath(lock);
1099 EXPORT_SYMBOL(mutex_lock_killable);
1101 static noinline void __sched
1102 __mutex_lock_slowpath(struct mutex *lock)
1104 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1107 static noinline int __sched
1108 __mutex_lock_killable_slowpath(struct mutex *lock)
1110 return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1113 static noinline int __sched
1114 __mutex_lock_interruptible_slowpath(struct mutex *lock)
1116 return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1119 static noinline int __sched
1120 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1122 return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
1126 static noinline int __sched
1127 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1128 struct ww_acquire_ctx *ctx)
1130 return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
1137 * mutex_trylock - try to acquire the mutex, without waiting
1138 * @lock: the mutex to be acquired
1140 * Try to acquire the mutex atomically. Returns 1 if the mutex
1141 * has been acquired successfully, and 0 on contention.
1143 * NOTE: this function follows the spin_trylock() convention, so
1144 * it is negated from the down_trylock() return values! Be careful
1145 * about this when converting semaphore users to mutexes.
1147 * This function must not be used in interrupt context. The
1148 * mutex must be released by the same task that acquired it.
1150 int __sched mutex_trylock(struct mutex *lock)
1152 bool locked = __mutex_trylock(lock);
1155 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1159 EXPORT_SYMBOL(mutex_trylock);
1161 #ifndef CONFIG_DEBUG_LOCK_ALLOC
1163 ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1167 if (__mutex_trylock_fast(&lock->base)) {
1169 ww_mutex_set_context_fastpath(lock, ctx);
1173 return __ww_mutex_lock_slowpath(lock, ctx);
1175 EXPORT_SYMBOL(ww_mutex_lock);
1178 ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1182 if (__mutex_trylock_fast(&lock->base)) {
1184 ww_mutex_set_context_fastpath(lock, ctx);
1188 return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1190 EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1195 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1196 * @cnt: the atomic which we are to dec
1197 * @lock: the mutex to return holding if we dec to 0
1199 * return true and hold lock if we dec to 0, return false otherwise
1201 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1203 /* dec if we can't possibly hit 0 */
1204 if (atomic_add_unless(cnt, -1, 1))
1206 /* we might hit 0, so take the lock */
1208 if (!atomic_dec_and_test(cnt)) {
1209 /* when we actually did the dec, we didn't hit 0 */
1213 /* we hit 0, and we hold the lock */
1216 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);