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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * kernel/locking/mutex.c
4 *
5 * Mutexes: blocking mutual exclusion locks
6 *
7 * Started by Ingo Molnar:
8 *
9 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <[email protected]>
10 *
11 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
12 * David Howells for suggestions and improvements.
13 *
14 * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
15 * from the -rt tree, where it was originally implemented for rtmutexes
16 * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
17 * and Sven Dietrich.
18 *
19 * Also see Documentation/locking/mutex-design.rst.
20 */
21#include <linux/mutex.h>
22#include <linux/ww_mutex.h>
23#include <linux/sched/signal.h>
24#include <linux/sched/rt.h>
25#include <linux/sched/wake_q.h>
26#include <linux/sched/debug.h>
27#include <linux/export.h>
28#include <linux/spinlock.h>
29#include <linux/interrupt.h>
30#include <linux/debug_locks.h>
31#include <linux/osq_lock.h>
32#include <linux/hung_task.h>
33
34#define CREATE_TRACE_POINTS
35#include <trace/events/lock.h>
36
37#ifndef CONFIG_PREEMPT_RT
38#include "mutex.h"
39
40#ifdef CONFIG_DEBUG_MUTEXES
41# define MUTEX_WARN_ON(cond) DEBUG_LOCKS_WARN_ON(cond)
42#else
43# define MUTEX_WARN_ON(cond)
44#endif
45
46static void __mutex_init_generic(struct mutex *lock)
47{
48 atomic_long_set(&lock->owner, 0);
49 raw_spin_lock_init(&lock->wait_lock);
50 INIT_LIST_HEAD(&lock->wait_list);
51#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
52 osq_lock_init(&lock->osq);
53#endif
54 debug_mutex_init(lock);
55}
56
57static inline struct task_struct *__owner_task(unsigned long owner)
58{
59 return (struct task_struct *)(owner & ~MUTEX_FLAGS);
60}
61
62bool mutex_is_locked(struct mutex *lock)
63{
64 return __mutex_owner(lock) != NULL;
65}
66EXPORT_SYMBOL(mutex_is_locked);
67
68static inline unsigned long __owner_flags(unsigned long owner)
69{
70 return owner & MUTEX_FLAGS;
71}
72
73/* Do not use the return value as a pointer directly. */
74unsigned long mutex_get_owner(struct mutex *lock)
75{
76 unsigned long owner = atomic_long_read(&lock->owner);
77
78 return (unsigned long)__owner_task(owner);
79}
80
81/*
82 * Returns: __mutex_owner(lock) on failure or NULL on success.
83 */
84static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff)
85{
86 unsigned long owner, curr = (unsigned long)current;
87
88 owner = atomic_long_read(&lock->owner);
89 for (;;) { /* must loop, can race against a flag */
90 unsigned long flags = __owner_flags(owner);
91 unsigned long task = owner & ~MUTEX_FLAGS;
92
93 if (task) {
94 if (flags & MUTEX_FLAG_PICKUP) {
95 if (task != curr)
96 break;
97 flags &= ~MUTEX_FLAG_PICKUP;
98 } else if (handoff) {
99 if (flags & MUTEX_FLAG_HANDOFF)
100 break;
101 flags |= MUTEX_FLAG_HANDOFF;
102 } else {
103 break;
104 }
105 } else {
106 MUTEX_WARN_ON(flags & (MUTEX_FLAG_HANDOFF | MUTEX_FLAG_PICKUP));
107 task = curr;
108 }
109
110 if (atomic_long_try_cmpxchg_acquire(&lock->owner, &owner, task | flags)) {
111 if (task == curr)
112 return NULL;
113 break;
114 }
115 }
116
117 return __owner_task(owner);
118}
119
120/*
121 * Trylock or set HANDOFF
122 */
123static inline bool __mutex_trylock_or_handoff(struct mutex *lock, bool handoff)
124{
125 return !__mutex_trylock_common(lock, handoff);
126}
127
128/*
129 * Actual trylock that will work on any unlocked state.
130 */
131static inline bool __mutex_trylock(struct mutex *lock)
132{
133 return !__mutex_trylock_common(lock, false);
134}
135
136#ifndef CONFIG_DEBUG_LOCK_ALLOC
137/*
138 * Lockdep annotations are contained to the slow paths for simplicity.
139 * There is nothing that would stop spreading the lockdep annotations outwards
140 * except more code.
141 */
142void mutex_init_generic(struct mutex *lock)
143{
144 __mutex_init_generic(lock);
145}
146EXPORT_SYMBOL(mutex_init_generic);
147
148/*
149 * Optimistic trylock that only works in the uncontended case. Make sure to
150 * follow with a __mutex_trylock() before failing.
151 */
152static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
153{
154 unsigned long curr = (unsigned long)current;
155 unsigned long zero = 0UL;
156
157 MUTEX_WARN_ON(lock->magic != lock);
158
159 if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
160 return true;
161
162 return false;
163}
164
165static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
166{
167 unsigned long curr = (unsigned long)current;
168
169 return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
170}
171
172#else /* !CONFIG_DEBUG_LOCK_ALLOC */
173
174void mutex_init_lockep(struct mutex *lock, const char *name, struct lock_class_key *key)
175{
176 __mutex_init_generic(lock);
177
178 /*
179 * Make sure we are not reinitializing a held lock:
180 */
181 debug_check_no_locks_freed((void *)lock, sizeof(*lock));
182 lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_SLEEP);
183}
184EXPORT_SYMBOL(mutex_init_lockep);
185#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
186
187static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
188{
189 atomic_long_or(flag, &lock->owner);
190}
191
192static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
193{
194 atomic_long_andnot(flag, &lock->owner);
195}
196
197static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
198{
199 return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
200}
201
202/*
203 * Add @waiter to a given location in the lock wait_list and set the
204 * FLAG_WAITERS flag if it's the first waiter.
205 */
206static void
207__mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
208 struct list_head *list)
209{
210 hung_task_set_blocker(lock, BLOCKER_TYPE_MUTEX);
211 debug_mutex_add_waiter(lock, waiter, current);
212
213 list_add_tail(&waiter->list, list);
214 if (__mutex_waiter_is_first(lock, waiter))
215 __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
216}
217
218static void
219__mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter)
220{
221 list_del(&waiter->list);
222 if (likely(list_empty(&lock->wait_list)))
223 __mutex_clear_flag(lock, MUTEX_FLAGS);
224
225 debug_mutex_remove_waiter(lock, waiter, current);
226 hung_task_clear_blocker();
227}
228
229/*
230 * Give up ownership to a specific task, when @task = NULL, this is equivalent
231 * to a regular unlock. Sets PICKUP on a handoff, clears HANDOFF, preserves
232 * WAITERS. Provides RELEASE semantics like a regular unlock, the
233 * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
234 */
235static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
236{
237 unsigned long owner = atomic_long_read(&lock->owner);
238
239 for (;;) {
240 unsigned long new;
241
242 MUTEX_WARN_ON(__owner_task(owner) != current);
243 MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
244
245 new = (owner & MUTEX_FLAG_WAITERS);
246 new |= (unsigned long)task;
247 if (task)
248 new |= MUTEX_FLAG_PICKUP;
249
250 if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, new))
251 break;
252 }
253}
254
255#ifndef CONFIG_DEBUG_LOCK_ALLOC
256/*
257 * We split the mutex lock/unlock logic into separate fastpath and
258 * slowpath functions, to reduce the register pressure on the fastpath.
259 * We also put the fastpath first in the kernel image, to make sure the
260 * branch is predicted by the CPU as default-untaken.
261 */
262static void __sched __mutex_lock_slowpath(struct mutex *lock);
263
264/**
265 * mutex_lock - acquire the mutex
266 * @lock: the mutex to be acquired
267 *
268 * Lock the mutex exclusively for this task. If the mutex is not
269 * available right now, it will sleep until it can get it.
270 *
271 * The mutex must later on be released by the same task that
272 * acquired it. Recursive locking is not allowed. The task
273 * may not exit without first unlocking the mutex. Also, kernel
274 * memory where the mutex resides must not be freed with
275 * the mutex still locked. The mutex must first be initialized
276 * (or statically defined) before it can be locked. memset()-ing
277 * the mutex to 0 is not allowed.
278 *
279 * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
280 * checks that will enforce the restrictions and will also do
281 * deadlock debugging)
282 *
283 * This function is similar to (but not equivalent to) down().
284 */
285void __sched mutex_lock(struct mutex *lock)
286{
287 might_sleep();
288
289 if (!__mutex_trylock_fast(lock))
290 __mutex_lock_slowpath(lock);
291}
292EXPORT_SYMBOL(mutex_lock);
293#endif
294
295#include "ww_mutex.h"
296
297#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
298
299/*
300 * Trylock variant that returns the owning task on failure.
301 */
302static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
303{
304 return __mutex_trylock_common(lock, false);
305}
306
307static inline
308bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
309 struct mutex_waiter *waiter)
310{
311 struct ww_mutex *ww;
312
313 ww = container_of(lock, struct ww_mutex, base);
314
315 /*
316 * If ww->ctx is set the contents are undefined, only
317 * by acquiring wait_lock there is a guarantee that
318 * they are not invalid when reading.
319 *
320 * As such, when deadlock detection needs to be
321 * performed the optimistic spinning cannot be done.
322 *
323 * Check this in every inner iteration because we may
324 * be racing against another thread's ww_mutex_lock.
325 */
326 if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
327 return false;
328
329 /*
330 * If we aren't on the wait list yet, cancel the spin
331 * if there are waiters. We want to avoid stealing the
332 * lock from a waiter with an earlier stamp, since the
333 * other thread may already own a lock that we also
334 * need.
335 */
336 if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
337 return false;
338
339 /*
340 * Similarly, stop spinning if we are no longer the
341 * first waiter.
342 */
343 if (waiter && !__mutex_waiter_is_first(lock, waiter))
344 return false;
345
346 return true;
347}
348
349/*
350 * Look out! "owner" is an entirely speculative pointer access and not
351 * reliable.
352 *
353 * "noinline" so that this function shows up on perf profiles.
354 */
355static noinline
356bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
357 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
358{
359 bool ret = true;
360
361 lockdep_assert_preemption_disabled();
362
363 while (__mutex_owner(lock) == owner) {
364 /*
365 * Ensure we emit the owner->on_cpu, dereference _after_
366 * checking lock->owner still matches owner. And we already
367 * disabled preemption which is equal to the RCU read-side
368 * crital section in optimistic spinning code. Thus the
369 * task_strcut structure won't go away during the spinning
370 * period
371 */
372 barrier();
373
374 /*
375 * Use vcpu_is_preempted to detect lock holder preemption issue.
376 */
377 if (!owner_on_cpu(owner) || need_resched()) {
378 ret = false;
379 break;
380 }
381
382 if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
383 ret = false;
384 break;
385 }
386
387 cpu_relax();
388 }
389
390 return ret;
391}
392
393/*
394 * Initial check for entering the mutex spinning loop
395 */
396static inline int mutex_can_spin_on_owner(struct mutex *lock)
397{
398 struct task_struct *owner;
399 int retval = 1;
400
401 lockdep_assert_preemption_disabled();
402
403 if (need_resched())
404 return 0;
405
406 /*
407 * We already disabled preemption which is equal to the RCU read-side
408 * crital section in optimistic spinning code. Thus the task_strcut
409 * structure won't go away during the spinning period.
410 */
411 owner = __mutex_owner(lock);
412 if (owner)
413 retval = owner_on_cpu(owner);
414
415 /*
416 * If lock->owner is not set, the mutex has been released. Return true
417 * such that we'll trylock in the spin path, which is a faster option
418 * than the blocking slow path.
419 */
420 return retval;
421}
422
423/*
424 * Optimistic spinning.
425 *
426 * We try to spin for acquisition when we find that the lock owner
427 * is currently running on a (different) CPU and while we don't
428 * need to reschedule. The rationale is that if the lock owner is
429 * running, it is likely to release the lock soon.
430 *
431 * The mutex spinners are queued up using MCS lock so that only one
432 * spinner can compete for the mutex. However, if mutex spinning isn't
433 * going to happen, there is no point in going through the lock/unlock
434 * overhead.
435 *
436 * Returns true when the lock was taken, otherwise false, indicating
437 * that we need to jump to the slowpath and sleep.
438 *
439 * The waiter flag is set to true if the spinner is a waiter in the wait
440 * queue. The waiter-spinner will spin on the lock directly and concurrently
441 * with the spinner at the head of the OSQ, if present, until the owner is
442 * changed to itself.
443 */
444static __always_inline bool
445mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
446 struct mutex_waiter *waiter)
447{
448 if (!waiter) {
449 /*
450 * The purpose of the mutex_can_spin_on_owner() function is
451 * to eliminate the overhead of osq_lock() and osq_unlock()
452 * in case spinning isn't possible. As a waiter-spinner
453 * is not going to take OSQ lock anyway, there is no need
454 * to call mutex_can_spin_on_owner().
455 */
456 if (!mutex_can_spin_on_owner(lock))
457 goto fail;
458
459 /*
460 * In order to avoid a stampede of mutex spinners trying to
461 * acquire the mutex all at once, the spinners need to take a
462 * MCS (queued) lock first before spinning on the owner field.
463 */
464 if (!osq_lock(&lock->osq))
465 goto fail;
466 }
467
468 for (;;) {
469 struct task_struct *owner;
470
471 /* Try to acquire the mutex... */
472 owner = __mutex_trylock_or_owner(lock);
473 if (!owner)
474 break;
475
476 /*
477 * There's an owner, wait for it to either
478 * release the lock or go to sleep.
479 */
480 if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
481 goto fail_unlock;
482
483 /*
484 * The cpu_relax() call is a compiler barrier which forces
485 * everything in this loop to be re-loaded. We don't need
486 * memory barriers as we'll eventually observe the right
487 * values at the cost of a few extra spins.
488 */
489 cpu_relax();
490 }
491
492 if (!waiter)
493 osq_unlock(&lock->osq);
494
495 return true;
496
497
498fail_unlock:
499 if (!waiter)
500 osq_unlock(&lock->osq);
501
502fail:
503 /*
504 * If we fell out of the spin path because of need_resched(),
505 * reschedule now, before we try-lock the mutex. This avoids getting
506 * scheduled out right after we obtained the mutex.
507 */
508 if (need_resched()) {
509 /*
510 * We _should_ have TASK_RUNNING here, but just in case
511 * we do not, make it so, otherwise we might get stuck.
512 */
513 __set_current_state(TASK_RUNNING);
514 schedule_preempt_disabled();
515 }
516
517 return false;
518}
519#else
520static __always_inline bool
521mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
522 struct mutex_waiter *waiter)
523{
524 return false;
525}
526#endif
527
528static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
529
530/**
531 * mutex_unlock - release the mutex
532 * @lock: the mutex to be released
533 *
534 * Unlock a mutex that has been locked by this task previously.
535 *
536 * This function must not be used in interrupt context. Unlocking
537 * of a not locked mutex is not allowed.
538 *
539 * The caller must ensure that the mutex stays alive until this function has
540 * returned - mutex_unlock() can NOT directly be used to release an object such
541 * that another concurrent task can free it.
542 * Mutexes are different from spinlocks & refcounts in this aspect.
543 *
544 * This function is similar to (but not equivalent to) up().
545 */
546void __sched mutex_unlock(struct mutex *lock)
547{
548#ifndef CONFIG_DEBUG_LOCK_ALLOC
549 if (__mutex_unlock_fast(lock))
550 return;
551#endif
552 __mutex_unlock_slowpath(lock, _RET_IP_);
553}
554EXPORT_SYMBOL(mutex_unlock);
555
556/**
557 * ww_mutex_unlock - release the w/w mutex
558 * @lock: the mutex to be released
559 *
560 * Unlock a mutex that has been locked by this task previously with any of the
561 * ww_mutex_lock* functions (with or without an acquire context). It is
562 * forbidden to release the locks after releasing the acquire context.
563 *
564 * This function must not be used in interrupt context. Unlocking
565 * of a unlocked mutex is not allowed.
566 */
567void __sched ww_mutex_unlock(struct ww_mutex *lock)
568{
569 __ww_mutex_unlock(lock);
570 mutex_unlock(&lock->base);
571}
572EXPORT_SYMBOL(ww_mutex_unlock);
573
574/*
575 * Lock a mutex (possibly interruptible), slowpath:
576 */
577static __always_inline int __sched
578__mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclass,
579 struct lockdep_map *nest_lock, unsigned long ip,
580 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
581{
582 DEFINE_WAKE_Q(wake_q);
583 struct mutex_waiter waiter;
584 struct ww_mutex *ww;
585 unsigned long flags;
586 int ret;
587
588 if (!use_ww_ctx)
589 ww_ctx = NULL;
590
591 might_sleep();
592
593 MUTEX_WARN_ON(lock->magic != lock);
594
595 ww = container_of(lock, struct ww_mutex, base);
596 if (ww_ctx) {
597 if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
598 return -EALREADY;
599
600 /*
601 * Reset the wounded flag after a kill. No other process can
602 * race and wound us here since they can't have a valid owner
603 * pointer if we don't have any locks held.
604 */
605 if (ww_ctx->acquired == 0)
606 ww_ctx->wounded = 0;
607
608#ifdef CONFIG_DEBUG_LOCK_ALLOC
609 nest_lock = &ww_ctx->dep_map;
610#endif
611 }
612
613 preempt_disable();
614 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
615
616 trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);
617 if (__mutex_trylock(lock) ||
618 mutex_optimistic_spin(lock, ww_ctx, NULL)) {
619 /* got the lock, yay! */
620 lock_acquired(&lock->dep_map, ip);
621 if (ww_ctx)
622 ww_mutex_set_context_fastpath(ww, ww_ctx);
623 trace_contention_end(lock, 0);
624 preempt_enable();
625 return 0;
626 }
627
628 raw_spin_lock_irqsave(&lock->wait_lock, flags);
629 /*
630 * After waiting to acquire the wait_lock, try again.
631 */
632 if (__mutex_trylock(lock)) {
633 if (ww_ctx)
634 __ww_mutex_check_waiters(lock, ww_ctx, &wake_q);
635
636 goto skip_wait;
637 }
638
639 debug_mutex_lock_common(lock, &waiter);
640 waiter.task = current;
641 if (use_ww_ctx)
642 waiter.ww_ctx = ww_ctx;
643
644 lock_contended(&lock->dep_map, ip);
645
646 if (!use_ww_ctx) {
647 /* add waiting tasks to the end of the waitqueue (FIFO): */
648 __mutex_add_waiter(lock, &waiter, &lock->wait_list);
649 } else {
650 /*
651 * Add in stamp order, waking up waiters that must kill
652 * themselves.
653 */
654 ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx, &wake_q);
655 if (ret)
656 goto err_early_kill;
657 }
658
659 __set_task_blocked_on(current, lock);
660 set_current_state(state);
661 trace_contention_begin(lock, LCB_F_MUTEX);
662 for (;;) {
663 bool first;
664
665 /*
666 * Once we hold wait_lock, we're serialized against
667 * mutex_unlock() handing the lock off to us, do a trylock
668 * before testing the error conditions to make sure we pick up
669 * the handoff.
670 */
671 if (__mutex_trylock(lock))
672 goto acquired;
673
674 /*
675 * Check for signals and kill conditions while holding
676 * wait_lock. This ensures the lock cancellation is ordered
677 * against mutex_unlock() and wake-ups do not go missing.
678 */
679 if (signal_pending_state(state, current)) {
680 ret = -EINTR;
681 goto err;
682 }
683
684 if (ww_ctx) {
685 ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
686 if (ret)
687 goto err;
688 }
689
690 raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
691
692 schedule_preempt_disabled();
693
694 first = __mutex_waiter_is_first(lock, &waiter);
695
696 /*
697 * As we likely have been woken up by task
698 * that has cleared our blocked_on state, re-set
699 * it to the lock we are trying to acquire.
700 */
701 set_task_blocked_on(current, lock);
702 set_current_state(state);
703 /*
704 * Here we order against unlock; we must either see it change
705 * state back to RUNNING and fall through the next schedule(),
706 * or we must see its unlock and acquire.
707 */
708 if (__mutex_trylock_or_handoff(lock, first))
709 break;
710
711 if (first) {
712 trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);
713 /*
714 * mutex_optimistic_spin() can call schedule(), so
715 * clear blocked on so we don't become unselectable
716 * to run.
717 */
718 clear_task_blocked_on(current, lock);
719 if (mutex_optimistic_spin(lock, ww_ctx, &waiter))
720 break;
721 set_task_blocked_on(current, lock);
722 trace_contention_begin(lock, LCB_F_MUTEX);
723 }
724
725 raw_spin_lock_irqsave(&lock->wait_lock, flags);
726 }
727 raw_spin_lock_irqsave(&lock->wait_lock, flags);
728acquired:
729 __clear_task_blocked_on(current, lock);
730 __set_current_state(TASK_RUNNING);
731
732 if (ww_ctx) {
733 /*
734 * Wound-Wait; we stole the lock (!first_waiter), check the
735 * waiters as anyone might want to wound us.
736 */
737 if (!ww_ctx->is_wait_die &&
738 !__mutex_waiter_is_first(lock, &waiter))
739 __ww_mutex_check_waiters(lock, ww_ctx, &wake_q);
740 }
741
742 __mutex_remove_waiter(lock, &waiter);
743
744 debug_mutex_free_waiter(&waiter);
745
746skip_wait:
747 /* got the lock - cleanup and rejoice! */
748 lock_acquired(&lock->dep_map, ip);
749 trace_contention_end(lock, 0);
750
751 if (ww_ctx)
752 ww_mutex_lock_acquired(ww, ww_ctx);
753
754 raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
755 preempt_enable();
756 return 0;
757
758err:
759 __clear_task_blocked_on(current, lock);
760 __set_current_state(TASK_RUNNING);
761 __mutex_remove_waiter(lock, &waiter);
762err_early_kill:
763 WARN_ON(__get_task_blocked_on(current));
764 trace_contention_end(lock, ret);
765 raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
766 debug_mutex_free_waiter(&waiter);
767 mutex_release(&lock->dep_map, ip);
768 preempt_enable();
769 return ret;
770}
771
772static int __sched
773__mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
774 struct lockdep_map *nest_lock, unsigned long ip)
775{
776 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
777}
778
779static int __sched
780__ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
781 unsigned long ip, struct ww_acquire_ctx *ww_ctx)
782{
783 return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
784}
785
786/**
787 * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
788 * @ww: mutex to lock
789 * @ww_ctx: optional w/w acquire context
790 *
791 * Trylocks a mutex with the optional acquire context; no deadlock detection is
792 * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
793 *
794 * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
795 * specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
796 *
797 * A mutex acquired with this function must be released with ww_mutex_unlock.
798 */
799int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
800{
801 if (!ww_ctx)
802 return mutex_trylock(&ww->base);
803
804 MUTEX_WARN_ON(ww->base.magic != &ww->base);
805
806 /*
807 * Reset the wounded flag after a kill. No other process can
808 * race and wound us here, since they can't have a valid owner
809 * pointer if we don't have any locks held.
810 */
811 if (ww_ctx->acquired == 0)
812 ww_ctx->wounded = 0;
813
814 if (__mutex_trylock(&ww->base)) {
815 ww_mutex_set_context_fastpath(ww, ww_ctx);
816 mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
817 return 1;
818 }
819
820 return 0;
821}
822EXPORT_SYMBOL(ww_mutex_trylock);
823
824#ifdef CONFIG_DEBUG_LOCK_ALLOC
825void __sched
826mutex_lock_nested(struct mutex *lock, unsigned int subclass)
827{
828 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
829}
830
831EXPORT_SYMBOL_GPL(mutex_lock_nested);
832
833void __sched
834_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
835{
836 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
837}
838EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
839
840int __sched
841_mutex_lock_killable(struct mutex *lock, unsigned int subclass,
842 struct lockdep_map *nest)
843{
844 return __mutex_lock(lock, TASK_KILLABLE, subclass, nest, _RET_IP_);
845}
846EXPORT_SYMBOL_GPL(_mutex_lock_killable);
847
848int __sched
849mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
850{
851 return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
852}
853EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
854
855void __sched
856mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
857{
858 int token;
859
860 might_sleep();
861
862 token = io_schedule_prepare();
863 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
864 subclass, NULL, _RET_IP_, NULL, 0);
865 io_schedule_finish(token);
866}
867EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
868
869static inline int
870ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
871{
872#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
873 unsigned tmp;
874
875 if (ctx->deadlock_inject_countdown-- == 0) {
876 tmp = ctx->deadlock_inject_interval;
877 if (tmp > UINT_MAX/4)
878 tmp = UINT_MAX;
879 else
880 tmp = tmp*2 + tmp + tmp/2;
881
882 ctx->deadlock_inject_interval = tmp;
883 ctx->deadlock_inject_countdown = tmp;
884 ctx->contending_lock = lock;
885
886 ww_mutex_unlock(lock);
887
888 return -EDEADLK;
889 }
890#endif
891
892 return 0;
893}
894
895int __sched
896ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
897{
898 int ret;
899
900 might_sleep();
901 ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
902 0, _RET_IP_, ctx);
903 if (!ret && ctx && ctx->acquired > 1)
904 return ww_mutex_deadlock_injection(lock, ctx);
905
906 return ret;
907}
908EXPORT_SYMBOL_GPL(ww_mutex_lock);
909
910int __sched
911ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
912{
913 int ret;
914
915 might_sleep();
916 ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
917 0, _RET_IP_, ctx);
918
919 if (!ret && ctx && ctx->acquired > 1)
920 return ww_mutex_deadlock_injection(lock, ctx);
921
922 return ret;
923}
924EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
925
926#endif
927
928/*
929 * Release the lock, slowpath:
930 */
931static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
932{
933 struct task_struct *next = NULL;
934 DEFINE_WAKE_Q(wake_q);
935 unsigned long owner;
936 unsigned long flags;
937
938 mutex_release(&lock->dep_map, ip);
939
940 /*
941 * Release the lock before (potentially) taking the spinlock such that
942 * other contenders can get on with things ASAP.
943 *
944 * Except when HANDOFF, in that case we must not clear the owner field,
945 * but instead set it to the top waiter.
946 */
947 owner = atomic_long_read(&lock->owner);
948 for (;;) {
949 MUTEX_WARN_ON(__owner_task(owner) != current);
950 MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
951
952 if (owner & MUTEX_FLAG_HANDOFF)
953 break;
954
955 if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
956 if (owner & MUTEX_FLAG_WAITERS)
957 break;
958
959 return;
960 }
961 }
962
963 raw_spin_lock_irqsave(&lock->wait_lock, flags);
964 debug_mutex_unlock(lock);
965 if (!list_empty(&lock->wait_list)) {
966 /* get the first entry from the wait-list: */
967 struct mutex_waiter *waiter =
968 list_first_entry(&lock->wait_list,
969 struct mutex_waiter, list);
970
971 next = waiter->task;
972
973 debug_mutex_wake_waiter(lock, waiter);
974 __clear_task_blocked_on(next, lock);
975 wake_q_add(&wake_q, next);
976 }
977
978 if (owner & MUTEX_FLAG_HANDOFF)
979 __mutex_handoff(lock, next);
980
981 raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
982}
983
984#ifndef CONFIG_DEBUG_LOCK_ALLOC
985/*
986 * Here come the less common (and hence less performance-critical) APIs:
987 * mutex_lock_interruptible() and mutex_trylock().
988 */
989static noinline int __sched
990__mutex_lock_killable_slowpath(struct mutex *lock);
991
992static noinline int __sched
993__mutex_lock_interruptible_slowpath(struct mutex *lock);
994
995/**
996 * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
997 * @lock: The mutex to be acquired.
998 *
999 * Lock the mutex like mutex_lock(). If a signal is delivered while the
1000 * process is sleeping, this function will return without acquiring the
1001 * mutex.
1002 *
1003 * Context: Process context.
1004 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1005 * signal arrived.
1006 */
1007int __sched mutex_lock_interruptible(struct mutex *lock)
1008{
1009 might_sleep();
1010
1011 if (__mutex_trylock_fast(lock))
1012 return 0;
1013
1014 return __mutex_lock_interruptible_slowpath(lock);
1015}
1016
1017EXPORT_SYMBOL(mutex_lock_interruptible);
1018
1019/**
1020 * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
1021 * @lock: The mutex to be acquired.
1022 *
1023 * Lock the mutex like mutex_lock(). If a signal which will be fatal to
1024 * the current process is delivered while the process is sleeping, this
1025 * function will return without acquiring the mutex.
1026 *
1027 * Context: Process context.
1028 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1029 * fatal signal arrived.
1030 */
1031int __sched mutex_lock_killable(struct mutex *lock)
1032{
1033 might_sleep();
1034
1035 if (__mutex_trylock_fast(lock))
1036 return 0;
1037
1038 return __mutex_lock_killable_slowpath(lock);
1039}
1040EXPORT_SYMBOL(mutex_lock_killable);
1041
1042/**
1043 * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1044 * @lock: The mutex to be acquired.
1045 *
1046 * Lock the mutex like mutex_lock(). While the task is waiting for this
1047 * mutex, it will be accounted as being in the IO wait state by the
1048 * scheduler.
1049 *
1050 * Context: Process context.
1051 */
1052void __sched mutex_lock_io(struct mutex *lock)
1053{
1054 int token;
1055
1056 token = io_schedule_prepare();
1057 mutex_lock(lock);
1058 io_schedule_finish(token);
1059}
1060EXPORT_SYMBOL_GPL(mutex_lock_io);
1061
1062static noinline void __sched
1063__mutex_lock_slowpath(struct mutex *lock)
1064{
1065 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1066}
1067
1068static noinline int __sched
1069__mutex_lock_killable_slowpath(struct mutex *lock)
1070{
1071 return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1072}
1073
1074static noinline int __sched
1075__mutex_lock_interruptible_slowpath(struct mutex *lock)
1076{
1077 return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1078}
1079
1080static noinline int __sched
1081__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1082{
1083 return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0,
1084 _RET_IP_, ctx);
1085}
1086
1087static noinline int __sched
1088__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1089 struct ww_acquire_ctx *ctx)
1090{
1091 return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0,
1092 _RET_IP_, ctx);
1093}
1094
1095#endif
1096
1097#ifndef CONFIG_DEBUG_LOCK_ALLOC
1098/**
1099 * mutex_trylock - try to acquire the mutex, without waiting
1100 * @lock: the mutex to be acquired
1101 *
1102 * Try to acquire the mutex atomically. Returns 1 if the mutex
1103 * has been acquired successfully, and 0 on contention.
1104 *
1105 * NOTE: this function follows the spin_trylock() convention, so
1106 * it is negated from the down_trylock() return values! Be careful
1107 * about this when converting semaphore users to mutexes.
1108 *
1109 * This function must not be used in interrupt context. The
1110 * mutex must be released by the same task that acquired it.
1111 */
1112int __sched mutex_trylock(struct mutex *lock)
1113{
1114 MUTEX_WARN_ON(lock->magic != lock);
1115 return __mutex_trylock(lock);
1116}
1117EXPORT_SYMBOL(mutex_trylock);
1118#else
1119int __sched _mutex_trylock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock)
1120{
1121 bool locked;
1122
1123 MUTEX_WARN_ON(lock->magic != lock);
1124 locked = __mutex_trylock(lock);
1125 if (locked)
1126 mutex_acquire_nest(&lock->dep_map, 0, 1, nest_lock, _RET_IP_);
1127
1128 return locked;
1129}
1130EXPORT_SYMBOL(_mutex_trylock_nest_lock);
1131#endif
1132
1133#ifndef CONFIG_DEBUG_LOCK_ALLOC
1134int __sched
1135ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1136{
1137 might_sleep();
1138
1139 if (__mutex_trylock_fast(&lock->base)) {
1140 if (ctx)
1141 ww_mutex_set_context_fastpath(lock, ctx);
1142 return 0;
1143 }
1144
1145 return __ww_mutex_lock_slowpath(lock, ctx);
1146}
1147EXPORT_SYMBOL(ww_mutex_lock);
1148
1149int __sched
1150ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1151{
1152 might_sleep();
1153
1154 if (__mutex_trylock_fast(&lock->base)) {
1155 if (ctx)
1156 ww_mutex_set_context_fastpath(lock, ctx);
1157 return 0;
1158 }
1159
1160 return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1161}
1162EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1163
1164#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
1165#endif /* !CONFIG_PREEMPT_RT */
1166
1167EXPORT_TRACEPOINT_SYMBOL_GPL(contention_begin);
1168EXPORT_TRACEPOINT_SYMBOL_GPL(contention_end);
1169
1170/**
1171 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1172 * @cnt: the atomic which we are to dec
1173 * @lock: the mutex to return holding if we dec to 0
1174 *
1175 * return true and hold lock if we dec to 0, return false otherwise
1176 */
1177int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1178{
1179 /* dec if we can't possibly hit 0 */
1180 if (atomic_add_unless(cnt, -1, 1))
1181 return 0;
1182 /* we might hit 0, so take the lock */
1183 mutex_lock(lock);
1184 if (!atomic_dec_and_test(cnt)) {
1185 /* when we actually did the dec, we didn't hit 0 */
1186 mutex_unlock(lock);
1187 return 0;
1188 }
1189 /* we hit 0, and we hold the lock */
1190 return 1;
1191}
1192EXPORT_SYMBOL(atomic_dec_and_mutex_lock);