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