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1/*
2 * kernel/locking/mutex.c
3 *
4 * Mutexes: blocking mutual exclusion locks
5 *
6 * Started by Ingo Molnar:
7 *
8 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
9 *
10 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
11 * David Howells for suggestions and improvements.
12 *
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
16 * and Sven Dietrich.
17 *
18 * Also see Documentation/mutex-design.txt.
19 */
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 "mcs_spinlock.h"
29
30/*
31 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
32 * which forces all calls into the slowpath:
33 */
34#ifdef CONFIG_DEBUG_MUTEXES
35# include "mutex-debug.h"
36# include <asm-generic/mutex-null.h>
37/*
38 * Must be 0 for the debug case so we do not do the unlock outside of the
39 * wait_lock region. debug_mutex_unlock() will do the actual unlock in this
40 * case.
41 */
42# undef __mutex_slowpath_needs_to_unlock
43# define __mutex_slowpath_needs_to_unlock() 0
44#else
45# include "mutex.h"
46# include <asm/mutex.h>
47#endif
48
49/*
50 * A negative mutex count indicates that waiters are sleeping waiting for the
51 * mutex.
52 */
53#define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) >= 0)
54
55void
56__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
57{
58 atomic_set(&lock->count, 1);
59 spin_lock_init(&lock->wait_lock);
60 INIT_LIST_HEAD(&lock->wait_list);
61 mutex_clear_owner(lock);
62#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
63 lock->osq = NULL;
64#endif
65
66 debug_mutex_init(lock, name, key);
67}
68
69EXPORT_SYMBOL(__mutex_init);
70
71#ifndef CONFIG_DEBUG_LOCK_ALLOC
72/*
73 * We split the mutex lock/unlock logic into separate fastpath and
74 * slowpath functions, to reduce the register pressure on the fastpath.
75 * We also put the fastpath first in the kernel image, to make sure the
76 * branch is predicted by the CPU as default-untaken.
77 */
78__visible void __sched __mutex_lock_slowpath(atomic_t *lock_count);
79
80/**
81 * mutex_lock - acquire the mutex
82 * @lock: the mutex to be acquired
83 *
84 * Lock the mutex exclusively for this task. If the mutex is not
85 * available right now, it will sleep until it can get it.
86 *
87 * The mutex must later on be released by the same task that
88 * acquired it. Recursive locking is not allowed. The task
89 * may not exit without first unlocking the mutex. Also, kernel
90 * memory where the mutex resides mutex must not be freed with
91 * the mutex still locked. The mutex must first be initialized
92 * (or statically defined) before it can be locked. memset()-ing
93 * the mutex to 0 is not allowed.
94 *
95 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
96 * checks that will enforce the restrictions and will also do
97 * deadlock debugging. )
98 *
99 * This function is similar to (but not equivalent to) down().
100 */
101void __sched mutex_lock(struct mutex *lock)
102{
103 might_sleep();
104 /*
105 * The locking fastpath is the 1->0 transition from
106 * 'unlocked' into 'locked' state.
107 */
108 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
109 mutex_set_owner(lock);
110}
111
112EXPORT_SYMBOL(mutex_lock);
113#endif
114
115#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
116/*
117 * In order to avoid a stampede of mutex spinners from acquiring the mutex
118 * more or less simultaneously, the spinners need to acquire a MCS lock
119 * first before spinning on the owner field.
120 *
121 */
122
123/*
124 * Mutex spinning code migrated from kernel/sched/core.c
125 */
126
127static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
128{
129 if (lock->owner != owner)
130 return false;
131
132 /*
133 * Ensure we emit the owner->on_cpu, dereference _after_ checking
134 * lock->owner still matches owner, if that fails, owner might
135 * point to free()d memory, if it still matches, the rcu_read_lock()
136 * ensures the memory stays valid.
137 */
138 barrier();
139
140 return owner->on_cpu;
141}
142
143/*
144 * Look out! "owner" is an entirely speculative pointer
145 * access and not reliable.
146 */
147static noinline
148int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
149{
150 rcu_read_lock();
151 while (owner_running(lock, owner)) {
152 if (need_resched())
153 break;
154
155 arch_mutex_cpu_relax();
156 }
157 rcu_read_unlock();
158
159 /*
160 * We break out the loop above on need_resched() and when the
161 * owner changed, which is a sign for heavy contention. Return
162 * success only when lock->owner is NULL.
163 */
164 return lock->owner == NULL;
165}
166
167/*
168 * Initial check for entering the mutex spinning loop
169 */
170static inline int mutex_can_spin_on_owner(struct mutex *lock)
171{
172 struct task_struct *owner;
173 int retval = 1;
174
175 if (need_resched())
176 return 0;
177
178 rcu_read_lock();
179 owner = ACCESS_ONCE(lock->owner);
180 if (owner)
181 retval = owner->on_cpu;
182 rcu_read_unlock();
183 /*
184 * if lock->owner is not set, the mutex owner may have just acquired
185 * it and not set the owner yet or the mutex has been released.
186 */
187 return retval;
188}
189#endif
190
191__visible __used noinline
192void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
193
194/**
195 * mutex_unlock - release the mutex
196 * @lock: the mutex to be released
197 *
198 * Unlock a mutex that has been locked by this task previously.
199 *
200 * This function must not be used in interrupt context. Unlocking
201 * of a not locked mutex is not allowed.
202 *
203 * This function is similar to (but not equivalent to) up().
204 */
205void __sched mutex_unlock(struct mutex *lock)
206{
207 /*
208 * The unlocking fastpath is the 0->1 transition from 'locked'
209 * into 'unlocked' state:
210 */
211#ifndef CONFIG_DEBUG_MUTEXES
212 /*
213 * When debugging is enabled we must not clear the owner before time,
214 * the slow path will always be taken, and that clears the owner field
215 * after verifying that it was indeed current.
216 */
217 mutex_clear_owner(lock);
218#endif
219 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
220}
221
222EXPORT_SYMBOL(mutex_unlock);
223
224/**
225 * ww_mutex_unlock - release the w/w mutex
226 * @lock: the mutex to be released
227 *
228 * Unlock a mutex that has been locked by this task previously with any of the
229 * ww_mutex_lock* functions (with or without an acquire context). It is
230 * forbidden to release the locks after releasing the acquire context.
231 *
232 * This function must not be used in interrupt context. Unlocking
233 * of a unlocked mutex is not allowed.
234 */
235void __sched ww_mutex_unlock(struct ww_mutex *lock)
236{
237 /*
238 * The unlocking fastpath is the 0->1 transition from 'locked'
239 * into 'unlocked' state:
240 */
241 if (lock->ctx) {
242#ifdef CONFIG_DEBUG_MUTEXES
243 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
244#endif
245 if (lock->ctx->acquired > 0)
246 lock->ctx->acquired--;
247 lock->ctx = NULL;
248 }
249
250#ifndef CONFIG_DEBUG_MUTEXES
251 /*
252 * When debugging is enabled we must not clear the owner before time,
253 * the slow path will always be taken, and that clears the owner field
254 * after verifying that it was indeed current.
255 */
256 mutex_clear_owner(&lock->base);
257#endif
258 __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath);
259}
260EXPORT_SYMBOL(ww_mutex_unlock);
261
262static inline int __sched
263__mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
264{
265 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
266 struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx);
267
268 if (!hold_ctx)
269 return 0;
270
271 if (unlikely(ctx == hold_ctx))
272 return -EALREADY;
273
274 if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
275 (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
276#ifdef CONFIG_DEBUG_MUTEXES
277 DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
278 ctx->contending_lock = ww;
279#endif
280 return -EDEADLK;
281 }
282
283 return 0;
284}
285
286static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
287 struct ww_acquire_ctx *ww_ctx)
288{
289#ifdef CONFIG_DEBUG_MUTEXES
290 /*
291 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
292 * but released with a normal mutex_unlock in this call.
293 *
294 * This should never happen, always use ww_mutex_unlock.
295 */
296 DEBUG_LOCKS_WARN_ON(ww->ctx);
297
298 /*
299 * Not quite done after calling ww_acquire_done() ?
300 */
301 DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
302
303 if (ww_ctx->contending_lock) {
304 /*
305 * After -EDEADLK you tried to
306 * acquire a different ww_mutex? Bad!
307 */
308 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
309
310 /*
311 * You called ww_mutex_lock after receiving -EDEADLK,
312 * but 'forgot' to unlock everything else first?
313 */
314 DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
315 ww_ctx->contending_lock = NULL;
316 }
317
318 /*
319 * Naughty, using a different class will lead to undefined behavior!
320 */
321 DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
322#endif
323 ww_ctx->acquired++;
324}
325
326/*
327 * after acquiring lock with fastpath or when we lost out in contested
328 * slowpath, set ctx and wake up any waiters so they can recheck.
329 *
330 * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
331 * as the fastpath and opportunistic spinning are disabled in that case.
332 */
333static __always_inline void
334ww_mutex_set_context_fastpath(struct ww_mutex *lock,
335 struct ww_acquire_ctx *ctx)
336{
337 unsigned long flags;
338 struct mutex_waiter *cur;
339
340 ww_mutex_lock_acquired(lock, ctx);
341
342 lock->ctx = ctx;
343
344 /*
345 * The lock->ctx update should be visible on all cores before
346 * the atomic read is done, otherwise contended waiters might be
347 * missed. The contended waiters will either see ww_ctx == NULL
348 * and keep spinning, or it will acquire wait_lock, add itself
349 * to waiter list and sleep.
350 */
351 smp_mb(); /* ^^^ */
352
353 /*
354 * Check if lock is contended, if not there is nobody to wake up
355 */
356 if (likely(atomic_read(&lock->base.count) == 0))
357 return;
358
359 /*
360 * Uh oh, we raced in fastpath, wake up everyone in this case,
361 * so they can see the new lock->ctx.
362 */
363 spin_lock_mutex(&lock->base.wait_lock, flags);
364 list_for_each_entry(cur, &lock->base.wait_list, list) {
365 debug_mutex_wake_waiter(&lock->base, cur);
366 wake_up_process(cur->task);
367 }
368 spin_unlock_mutex(&lock->base.wait_lock, flags);
369}
370
371/*
372 * Lock a mutex (possibly interruptible), slowpath:
373 */
374static __always_inline int __sched
375__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
376 struct lockdep_map *nest_lock, unsigned long ip,
377 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
378{
379 struct task_struct *task = current;
380 struct mutex_waiter waiter;
381 unsigned long flags;
382 int ret;
383
384 preempt_disable();
385 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
386
387#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
388 /*
389 * Optimistic spinning.
390 *
391 * We try to spin for acquisition when we find that there are no
392 * pending waiters and the lock owner is currently running on a
393 * (different) CPU.
394 *
395 * The rationale is that if the lock owner is running, it is likely to
396 * release the lock soon.
397 *
398 * Since this needs the lock owner, and this mutex implementation
399 * doesn't track the owner atomically in the lock field, we need to
400 * track it non-atomically.
401 *
402 * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
403 * to serialize everything.
404 *
405 * The mutex spinners are queued up using MCS lock so that only one
406 * spinner can compete for the mutex. However, if mutex spinning isn't
407 * going to happen, there is no point in going through the lock/unlock
408 * overhead.
409 */
410 if (!mutex_can_spin_on_owner(lock))
411 goto slowpath;
412
413 if (!osq_lock(&lock->osq))
414 goto slowpath;
415
416 for (;;) {
417 struct task_struct *owner;
418
419 if (use_ww_ctx && ww_ctx->acquired > 0) {
420 struct ww_mutex *ww;
421
422 ww = container_of(lock, struct ww_mutex, base);
423 /*
424 * If ww->ctx is set the contents are undefined, only
425 * by acquiring wait_lock there is a guarantee that
426 * they are not invalid when reading.
427 *
428 * As such, when deadlock detection needs to be
429 * performed the optimistic spinning cannot be done.
430 */
431 if (ACCESS_ONCE(ww->ctx))
432 break;
433 }
434
435 /*
436 * If there's an owner, wait for it to either
437 * release the lock or go to sleep.
438 */
439 owner = ACCESS_ONCE(lock->owner);
440 if (owner && !mutex_spin_on_owner(lock, owner))
441 break;
442
443 if ((atomic_read(&lock->count) == 1) &&
444 (atomic_cmpxchg(&lock->count, 1, 0) == 1)) {
445 lock_acquired(&lock->dep_map, ip);
446 if (use_ww_ctx) {
447 struct ww_mutex *ww;
448 ww = container_of(lock, struct ww_mutex, base);
449
450 ww_mutex_set_context_fastpath(ww, ww_ctx);
451 }
452
453 mutex_set_owner(lock);
454 osq_unlock(&lock->osq);
455 preempt_enable();
456 return 0;
457 }
458
459 /*
460 * When there's no owner, we might have preempted between the
461 * owner acquiring the lock and setting the owner field. If
462 * we're an RT task that will live-lock because we won't let
463 * the owner complete.
464 */
465 if (!owner && (need_resched() || rt_task(task)))
466 break;
467
468 /*
469 * The cpu_relax() call is a compiler barrier which forces
470 * everything in this loop to be re-loaded. We don't need
471 * memory barriers as we'll eventually observe the right
472 * values at the cost of a few extra spins.
473 */
474 arch_mutex_cpu_relax();
475 }
476 osq_unlock(&lock->osq);
477slowpath:
478 /*
479 * If we fell out of the spin path because of need_resched(),
480 * reschedule now, before we try-lock the mutex. This avoids getting
481 * scheduled out right after we obtained the mutex.
482 */
483 if (need_resched())
484 schedule_preempt_disabled();
485#endif
486 spin_lock_mutex(&lock->wait_lock, flags);
487
488 /* once more, can we acquire the lock? */
489 if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, 0) == 1))
490 goto skip_wait;
491
492 debug_mutex_lock_common(lock, &waiter);
493 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
494
495 /* add waiting tasks to the end of the waitqueue (FIFO): */
496 list_add_tail(&waiter.list, &lock->wait_list);
497 waiter.task = task;
498
499 lock_contended(&lock->dep_map, ip);
500
501 for (;;) {
502 /*
503 * Lets try to take the lock again - this is needed even if
504 * we get here for the first time (shortly after failing to
505 * acquire the lock), to make sure that we get a wakeup once
506 * it's unlocked. Later on, if we sleep, this is the
507 * operation that gives us the lock. We xchg it to -1, so
508 * that when we release the lock, we properly wake up the
509 * other waiters:
510 */
511 if (MUTEX_SHOW_NO_WAITER(lock) &&
512 (atomic_xchg(&lock->count, -1) == 1))
513 break;
514
515 /*
516 * got a signal? (This code gets eliminated in the
517 * TASK_UNINTERRUPTIBLE case.)
518 */
519 if (unlikely(signal_pending_state(state, task))) {
520 ret = -EINTR;
521 goto err;
522 }
523
524 if (use_ww_ctx && ww_ctx->acquired > 0) {
525 ret = __mutex_lock_check_stamp(lock, ww_ctx);
526 if (ret)
527 goto err;
528 }
529
530 __set_task_state(task, state);
531
532 /* didn't get the lock, go to sleep: */
533 spin_unlock_mutex(&lock->wait_lock, flags);
534 schedule_preempt_disabled();
535 spin_lock_mutex(&lock->wait_lock, flags);
536 }
537 mutex_remove_waiter(lock, &waiter, current_thread_info());
538 /* set it to 0 if there are no waiters left: */
539 if (likely(list_empty(&lock->wait_list)))
540 atomic_set(&lock->count, 0);
541 debug_mutex_free_waiter(&waiter);
542
543skip_wait:
544 /* got the lock - cleanup and rejoice! */
545 lock_acquired(&lock->dep_map, ip);
546 mutex_set_owner(lock);
547
548 if (use_ww_ctx) {
549 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
550 struct mutex_waiter *cur;
551
552 /*
553 * This branch gets optimized out for the common case,
554 * and is only important for ww_mutex_lock.
555 */
556 ww_mutex_lock_acquired(ww, ww_ctx);
557 ww->ctx = ww_ctx;
558
559 /*
560 * Give any possible sleeping processes the chance to wake up,
561 * so they can recheck if they have to back off.
562 */
563 list_for_each_entry(cur, &lock->wait_list, list) {
564 debug_mutex_wake_waiter(lock, cur);
565 wake_up_process(cur->task);
566 }
567 }
568
569 spin_unlock_mutex(&lock->wait_lock, flags);
570 preempt_enable();
571 return 0;
572
573err:
574 mutex_remove_waiter(lock, &waiter, task_thread_info(task));
575 spin_unlock_mutex(&lock->wait_lock, flags);
576 debug_mutex_free_waiter(&waiter);
577 mutex_release(&lock->dep_map, 1, ip);
578 preempt_enable();
579 return ret;
580}
581
582#ifdef CONFIG_DEBUG_LOCK_ALLOC
583void __sched
584mutex_lock_nested(struct mutex *lock, unsigned int subclass)
585{
586 might_sleep();
587 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
588 subclass, NULL, _RET_IP_, NULL, 0);
589}
590
591EXPORT_SYMBOL_GPL(mutex_lock_nested);
592
593void __sched
594_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
595{
596 might_sleep();
597 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
598 0, nest, _RET_IP_, NULL, 0);
599}
600
601EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
602
603int __sched
604mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
605{
606 might_sleep();
607 return __mutex_lock_common(lock, TASK_KILLABLE,
608 subclass, NULL, _RET_IP_, NULL, 0);
609}
610EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
611
612int __sched
613mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
614{
615 might_sleep();
616 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
617 subclass, NULL, _RET_IP_, NULL, 0);
618}
619
620EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
621
622static inline int
623ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
624{
625#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
626 unsigned tmp;
627
628 if (ctx->deadlock_inject_countdown-- == 0) {
629 tmp = ctx->deadlock_inject_interval;
630 if (tmp > UINT_MAX/4)
631 tmp = UINT_MAX;
632 else
633 tmp = tmp*2 + tmp + tmp/2;
634
635 ctx->deadlock_inject_interval = tmp;
636 ctx->deadlock_inject_countdown = tmp;
637 ctx->contending_lock = lock;
638
639 ww_mutex_unlock(lock);
640
641 return -EDEADLK;
642 }
643#endif
644
645 return 0;
646}
647
648int __sched
649__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
650{
651 int ret;
652
653 might_sleep();
654 ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
655 0, &ctx->dep_map, _RET_IP_, ctx, 1);
656 if (!ret && ctx->acquired > 1)
657 return ww_mutex_deadlock_injection(lock, ctx);
658
659 return ret;
660}
661EXPORT_SYMBOL_GPL(__ww_mutex_lock);
662
663int __sched
664__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
665{
666 int ret;
667
668 might_sleep();
669 ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
670 0, &ctx->dep_map, _RET_IP_, ctx, 1);
671
672 if (!ret && ctx->acquired > 1)
673 return ww_mutex_deadlock_injection(lock, ctx);
674
675 return ret;
676}
677EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
678
679#endif
680
681/*
682 * Release the lock, slowpath:
683 */
684static inline void
685__mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
686{
687 struct mutex *lock = container_of(lock_count, struct mutex, count);
688 unsigned long flags;
689
690 /*
691 * some architectures leave the lock unlocked in the fastpath failure
692 * case, others need to leave it locked. In the later case we have to
693 * unlock it here
694 */
695 if (__mutex_slowpath_needs_to_unlock())
696 atomic_set(&lock->count, 1);
697
698 spin_lock_mutex(&lock->wait_lock, flags);
699 mutex_release(&lock->dep_map, nested, _RET_IP_);
700 debug_mutex_unlock(lock);
701
702 if (!list_empty(&lock->wait_list)) {
703 /* get the first entry from the wait-list: */
704 struct mutex_waiter *waiter =
705 list_entry(lock->wait_list.next,
706 struct mutex_waiter, list);
707
708 debug_mutex_wake_waiter(lock, waiter);
709
710 wake_up_process(waiter->task);
711 }
712
713 spin_unlock_mutex(&lock->wait_lock, flags);
714}
715
716/*
717 * Release the lock, slowpath:
718 */
719__visible void
720__mutex_unlock_slowpath(atomic_t *lock_count)
721{
722 __mutex_unlock_common_slowpath(lock_count, 1);
723}
724
725#ifndef CONFIG_DEBUG_LOCK_ALLOC
726/*
727 * Here come the less common (and hence less performance-critical) APIs:
728 * mutex_lock_interruptible() and mutex_trylock().
729 */
730static noinline int __sched
731__mutex_lock_killable_slowpath(struct mutex *lock);
732
733static noinline int __sched
734__mutex_lock_interruptible_slowpath(struct mutex *lock);
735
736/**
737 * mutex_lock_interruptible - acquire the mutex, interruptible
738 * @lock: the mutex to be acquired
739 *
740 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
741 * been acquired or sleep until the mutex becomes available. If a
742 * signal arrives while waiting for the lock then this function
743 * returns -EINTR.
744 *
745 * This function is similar to (but not equivalent to) down_interruptible().
746 */
747int __sched mutex_lock_interruptible(struct mutex *lock)
748{
749 int ret;
750
751 might_sleep();
752 ret = __mutex_fastpath_lock_retval(&lock->count);
753 if (likely(!ret)) {
754 mutex_set_owner(lock);
755 return 0;
756 } else
757 return __mutex_lock_interruptible_slowpath(lock);
758}
759
760EXPORT_SYMBOL(mutex_lock_interruptible);
761
762int __sched mutex_lock_killable(struct mutex *lock)
763{
764 int ret;
765
766 might_sleep();
767 ret = __mutex_fastpath_lock_retval(&lock->count);
768 if (likely(!ret)) {
769 mutex_set_owner(lock);
770 return 0;
771 } else
772 return __mutex_lock_killable_slowpath(lock);
773}
774EXPORT_SYMBOL(mutex_lock_killable);
775
776__visible void __sched
777__mutex_lock_slowpath(atomic_t *lock_count)
778{
779 struct mutex *lock = container_of(lock_count, struct mutex, count);
780
781 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
782 NULL, _RET_IP_, NULL, 0);
783}
784
785static noinline int __sched
786__mutex_lock_killable_slowpath(struct mutex *lock)
787{
788 return __mutex_lock_common(lock, TASK_KILLABLE, 0,
789 NULL, _RET_IP_, NULL, 0);
790}
791
792static noinline int __sched
793__mutex_lock_interruptible_slowpath(struct mutex *lock)
794{
795 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
796 NULL, _RET_IP_, NULL, 0);
797}
798
799static noinline int __sched
800__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
801{
802 return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
803 NULL, _RET_IP_, ctx, 1);
804}
805
806static noinline int __sched
807__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
808 struct ww_acquire_ctx *ctx)
809{
810 return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
811 NULL, _RET_IP_, ctx, 1);
812}
813
814#endif
815
816/*
817 * Spinlock based trylock, we take the spinlock and check whether we
818 * can get the lock:
819 */
820static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
821{
822 struct mutex *lock = container_of(lock_count, struct mutex, count);
823 unsigned long flags;
824 int prev;
825
826 spin_lock_mutex(&lock->wait_lock, flags);
827
828 prev = atomic_xchg(&lock->count, -1);
829 if (likely(prev == 1)) {
830 mutex_set_owner(lock);
831 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
832 }
833
834 /* Set it back to 0 if there are no waiters: */
835 if (likely(list_empty(&lock->wait_list)))
836 atomic_set(&lock->count, 0);
837
838 spin_unlock_mutex(&lock->wait_lock, flags);
839
840 return prev == 1;
841}
842
843/**
844 * mutex_trylock - try to acquire the mutex, without waiting
845 * @lock: the mutex to be acquired
846 *
847 * Try to acquire the mutex atomically. Returns 1 if the mutex
848 * has been acquired successfully, and 0 on contention.
849 *
850 * NOTE: this function follows the spin_trylock() convention, so
851 * it is negated from the down_trylock() return values! Be careful
852 * about this when converting semaphore users to mutexes.
853 *
854 * This function must not be used in interrupt context. The
855 * mutex must be released by the same task that acquired it.
856 */
857int __sched mutex_trylock(struct mutex *lock)
858{
859 int ret;
860
861 ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
862 if (ret)
863 mutex_set_owner(lock);
864
865 return ret;
866}
867EXPORT_SYMBOL(mutex_trylock);
868
869#ifndef CONFIG_DEBUG_LOCK_ALLOC
870int __sched
871__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
872{
873 int ret;
874
875 might_sleep();
876
877 ret = __mutex_fastpath_lock_retval(&lock->base.count);
878
879 if (likely(!ret)) {
880 ww_mutex_set_context_fastpath(lock, ctx);
881 mutex_set_owner(&lock->base);
882 } else
883 ret = __ww_mutex_lock_slowpath(lock, ctx);
884 return ret;
885}
886EXPORT_SYMBOL(__ww_mutex_lock);
887
888int __sched
889__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
890{
891 int ret;
892
893 might_sleep();
894
895 ret = __mutex_fastpath_lock_retval(&lock->base.count);
896
897 if (likely(!ret)) {
898 ww_mutex_set_context_fastpath(lock, ctx);
899 mutex_set_owner(&lock->base);
900 } else
901 ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx);
902 return ret;
903}
904EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
905
906#endif
907
908/**
909 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
910 * @cnt: the atomic which we are to dec
911 * @lock: the mutex to return holding if we dec to 0
912 *
913 * return true and hold lock if we dec to 0, return false otherwise
914 */
915int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
916{
917 /* dec if we can't possibly hit 0 */
918 if (atomic_add_unless(cnt, -1, 1))
919 return 0;
920 /* we might hit 0, so take the lock */
921 mutex_lock(lock);
922 if (!atomic_dec_and_test(cnt)) {
923 /* when we actually did the dec, we didn't hit 0 */
924 mutex_unlock(lock);
925 return 0;
926 }
927 /* we hit 0, and we hold the lock */
928 return 1;
929}
930EXPORT_SYMBOL(atomic_dec_and_mutex_lock);