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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);
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 <mingo@redhat.com>
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#ifdef CONFIG_DEBUG_MUTEXES
34# include "mutex-debug.h"
35#else
36# include "mutex.h"
37#endif
38
39void
40__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
41{
42 atomic_long_set(&lock->owner, 0);
43 spin_lock_init(&lock->wait_lock);
44 INIT_LIST_HEAD(&lock->wait_list);
45#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
46 osq_lock_init(&lock->osq);
47#endif
48
49 debug_mutex_init(lock, name, key);
50}
51EXPORT_SYMBOL(__mutex_init);
52
53/*
54 * @owner: contains: 'struct task_struct *' to the current lock owner,
55 * NULL means not owned. Since task_struct pointers are aligned at
56 * at least L1_CACHE_BYTES, we have low bits to store extra state.
57 *
58 * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
59 * Bit1 indicates unlock needs to hand the lock to the top-waiter
60 * Bit2 indicates handoff has been done and we're waiting for pickup.
61 */
62#define MUTEX_FLAG_WAITERS 0x01
63#define MUTEX_FLAG_HANDOFF 0x02
64#define MUTEX_FLAG_PICKUP 0x04
65
66#define MUTEX_FLAGS 0x07
67
68/*
69 * Internal helper function; C doesn't allow us to hide it :/
70 *
71 * DO NOT USE (outside of mutex code).
72 */
73static inline struct task_struct *__mutex_owner(struct mutex *lock)
74{
75 return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
76}
77
78static inline struct task_struct *__owner_task(unsigned long owner)
79{
80 return (struct task_struct *)(owner & ~MUTEX_FLAGS);
81}
82
83bool mutex_is_locked(struct mutex *lock)
84{
85 return __mutex_owner(lock) != NULL;
86}
87EXPORT_SYMBOL(mutex_is_locked);
88
89__must_check enum mutex_trylock_recursive_enum
90mutex_trylock_recursive(struct mutex *lock)
91{
92 if (unlikely(__mutex_owner(lock) == current))
93 return MUTEX_TRYLOCK_RECURSIVE;
94
95 return mutex_trylock(lock);
96}
97EXPORT_SYMBOL(mutex_trylock_recursive);
98
99static inline unsigned long __owner_flags(unsigned long owner)
100{
101 return owner & MUTEX_FLAGS;
102}
103
104/*
105 * Trylock variant that retuns the owning task on failure.
106 */
107static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
108{
109 unsigned long owner, curr = (unsigned long)current;
110
111 owner = atomic_long_read(&lock->owner);
112 for (;;) { /* must loop, can race against a flag */
113 unsigned long old, flags = __owner_flags(owner);
114 unsigned long task = owner & ~MUTEX_FLAGS;
115
116 if (task) {
117 if (likely(task != curr))
118 break;
119
120 if (likely(!(flags & MUTEX_FLAG_PICKUP)))
121 break;
122
123 flags &= ~MUTEX_FLAG_PICKUP;
124 } else {
125#ifdef CONFIG_DEBUG_MUTEXES
126 DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
127#endif
128 }
129
130 /*
131 * We set the HANDOFF bit, we must make sure it doesn't live
132 * past the point where we acquire it. This would be possible
133 * if we (accidentally) set the bit on an unlocked mutex.
134 */
135 flags &= ~MUTEX_FLAG_HANDOFF;
136
137 old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
138 if (old == owner)
139 return NULL;
140
141 owner = old;
142 }
143
144 return __owner_task(owner);
145}
146
147/*
148 * Actual trylock that will work on any unlocked state.
149 */
150static inline bool __mutex_trylock(struct mutex *lock)
151{
152 return !__mutex_trylock_or_owner(lock);
153}
154
155#ifndef CONFIG_DEBUG_LOCK_ALLOC
156/*
157 * Lockdep annotations are contained to the slow paths for simplicity.
158 * There is nothing that would stop spreading the lockdep annotations outwards
159 * except more code.
160 */
161
162/*
163 * Optimistic trylock that only works in the uncontended case. Make sure to
164 * follow with a __mutex_trylock() before failing.
165 */
166static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
167{
168 unsigned long curr = (unsigned long)current;
169 unsigned long zero = 0UL;
170
171 if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
172 return true;
173
174 return false;
175}
176
177static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
178{
179 unsigned long curr = (unsigned long)current;
180
181 if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
182 return true;
183
184 return false;
185}
186#endif
187
188static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
189{
190 atomic_long_or(flag, &lock->owner);
191}
192
193static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
194{
195 atomic_long_andnot(flag, &lock->owner);
196}
197
198static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
199{
200 return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
201}
202
203/*
204 * Add @waiter to a given location in the lock wait_list and set the
205 * FLAG_WAITERS flag if it's the first waiter.
206 */
207static void __sched
208__mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
209 struct list_head *list)
210{
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
218/*
219 * Give up ownership to a specific task, when @task = NULL, this is equivalent
220 * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
221 * WAITERS. Provides RELEASE semantics like a regular unlock, the
222 * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
223 */
224static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
225{
226 unsigned long owner = atomic_long_read(&lock->owner);
227
228 for (;;) {
229 unsigned long old, new;
230
231#ifdef CONFIG_DEBUG_MUTEXES
232 DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
233 DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
234#endif
235
236 new = (owner & MUTEX_FLAG_WAITERS);
237 new |= (unsigned long)task;
238 if (task)
239 new |= MUTEX_FLAG_PICKUP;
240
241 old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
242 if (old == owner)
243 break;
244
245 owner = old;
246 }
247}
248
249#ifndef CONFIG_DEBUG_LOCK_ALLOC
250/*
251 * We split the mutex lock/unlock logic into separate fastpath and
252 * slowpath functions, to reduce the register pressure on the fastpath.
253 * We also put the fastpath first in the kernel image, to make sure the
254 * branch is predicted by the CPU as default-untaken.
255 */
256static void __sched __mutex_lock_slowpath(struct mutex *lock);
257
258/**
259 * mutex_lock - acquire the mutex
260 * @lock: the mutex to be acquired
261 *
262 * Lock the mutex exclusively for this task. If the mutex is not
263 * available right now, it will sleep until it can get it.
264 *
265 * The mutex must later on be released by the same task that
266 * acquired it. Recursive locking is not allowed. The task
267 * may not exit without first unlocking the mutex. Also, kernel
268 * memory where the mutex resides must not be freed with
269 * the mutex still locked. The mutex must first be initialized
270 * (or statically defined) before it can be locked. memset()-ing
271 * the mutex to 0 is not allowed.
272 *
273 * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
274 * checks that will enforce the restrictions and will also do
275 * deadlock debugging)
276 *
277 * This function is similar to (but not equivalent to) down().
278 */
279void __sched mutex_lock(struct mutex *lock)
280{
281 might_sleep();
282
283 if (!__mutex_trylock_fast(lock))
284 __mutex_lock_slowpath(lock);
285}
286EXPORT_SYMBOL(mutex_lock);
287#endif
288
289/*
290 * Wait-Die:
291 * The newer transactions are killed when:
292 * It (the new transaction) makes a request for a lock being held
293 * by an older transaction.
294 *
295 * Wound-Wait:
296 * The newer transactions are wounded when:
297 * An older transaction makes a request for a lock being held by
298 * the newer transaction.
299 */
300
301/*
302 * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
303 * it.
304 */
305static __always_inline void
306ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
307{
308#ifdef CONFIG_DEBUG_MUTEXES
309 /*
310 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
311 * but released with a normal mutex_unlock in this call.
312 *
313 * This should never happen, always use ww_mutex_unlock.
314 */
315 DEBUG_LOCKS_WARN_ON(ww->ctx);
316
317 /*
318 * Not quite done after calling ww_acquire_done() ?
319 */
320 DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
321
322 if (ww_ctx->contending_lock) {
323 /*
324 * After -EDEADLK you tried to
325 * acquire a different ww_mutex? Bad!
326 */
327 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
328
329 /*
330 * You called ww_mutex_lock after receiving -EDEADLK,
331 * but 'forgot' to unlock everything else first?
332 */
333 DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
334 ww_ctx->contending_lock = NULL;
335 }
336
337 /*
338 * Naughty, using a different class will lead to undefined behavior!
339 */
340 DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
341#endif
342 ww_ctx->acquired++;
343 ww->ctx = ww_ctx;
344}
345
346/*
347 * Determine if context @a is 'after' context @b. IOW, @a is a younger
348 * transaction than @b and depending on algorithm either needs to wait for
349 * @b or die.
350 */
351static inline bool __sched
352__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
353{
354
355 return (signed long)(a->stamp - b->stamp) > 0;
356}
357
358/*
359 * Wait-Die; wake a younger waiter context (when locks held) such that it can
360 * die.
361 *
362 * Among waiters with context, only the first one can have other locks acquired
363 * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
364 * __ww_mutex_check_kill() wake any but the earliest context.
365 */
366static bool __sched
367__ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
368 struct ww_acquire_ctx *ww_ctx)
369{
370 if (!ww_ctx->is_wait_die)
371 return false;
372
373 if (waiter->ww_ctx->acquired > 0 &&
374 __ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
375 debug_mutex_wake_waiter(lock, waiter);
376 wake_up_process(waiter->task);
377 }
378
379 return true;
380}
381
382/*
383 * Wound-Wait; wound a younger @hold_ctx if it holds the lock.
384 *
385 * Wound the lock holder if there are waiters with older transactions than
386 * the lock holders. Even if multiple waiters may wound the lock holder,
387 * it's sufficient that only one does.
388 */
389static bool __ww_mutex_wound(struct mutex *lock,
390 struct ww_acquire_ctx *ww_ctx,
391 struct ww_acquire_ctx *hold_ctx)
392{
393 struct task_struct *owner = __mutex_owner(lock);
394
395 lockdep_assert_held(&lock->wait_lock);
396
397 /*
398 * Possible through __ww_mutex_add_waiter() when we race with
399 * ww_mutex_set_context_fastpath(). In that case we'll get here again
400 * through __ww_mutex_check_waiters().
401 */
402 if (!hold_ctx)
403 return false;
404
405 /*
406 * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
407 * it cannot go away because we'll have FLAG_WAITERS set and hold
408 * wait_lock.
409 */
410 if (!owner)
411 return false;
412
413 if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
414 hold_ctx->wounded = 1;
415
416 /*
417 * wake_up_process() paired with set_current_state()
418 * inserts sufficient barriers to make sure @owner either sees
419 * it's wounded in __ww_mutex_check_kill() or has a
420 * wakeup pending to re-read the wounded state.
421 */
422 if (owner != current)
423 wake_up_process(owner);
424
425 return true;
426 }
427
428 return false;
429}
430
431/*
432 * We just acquired @lock under @ww_ctx, if there are later contexts waiting
433 * behind us on the wait-list, check if they need to die, or wound us.
434 *
435 * See __ww_mutex_add_waiter() for the list-order construction; basically the
436 * list is ordered by stamp, smallest (oldest) first.
437 *
438 * This relies on never mixing wait-die/wound-wait on the same wait-list;
439 * which is currently ensured by that being a ww_class property.
440 *
441 * The current task must not be on the wait list.
442 */
443static void __sched
444__ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
445{
446 struct mutex_waiter *cur;
447
448 lockdep_assert_held(&lock->wait_lock);
449
450 list_for_each_entry(cur, &lock->wait_list, list) {
451 if (!cur->ww_ctx)
452 continue;
453
454 if (__ww_mutex_die(lock, cur, ww_ctx) ||
455 __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
456 break;
457 }
458}
459
460/*
461 * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
462 * and wake up any waiters so they can recheck.
463 */
464static __always_inline void
465ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
466{
467 ww_mutex_lock_acquired(lock, ctx);
468
469 /*
470 * The lock->ctx update should be visible on all cores before
471 * the WAITERS check is done, otherwise contended waiters might be
472 * missed. The contended waiters will either see ww_ctx == NULL
473 * and keep spinning, or it will acquire wait_lock, add itself
474 * to waiter list and sleep.
475 */
476 smp_mb(); /* See comments above and below. */
477
478 /*
479 * [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
480 * MB MB
481 * [R] MUTEX_FLAG_WAITERS [R] ww->ctx
482 *
483 * The memory barrier above pairs with the memory barrier in
484 * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
485 * and/or !empty list.
486 */
487 if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
488 return;
489
490 /*
491 * Uh oh, we raced in fastpath, check if any of the waiters need to
492 * die or wound us.
493 */
494 spin_lock(&lock->base.wait_lock);
495 __ww_mutex_check_waiters(&lock->base, ctx);
496 spin_unlock(&lock->base.wait_lock);
497}
498
499#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
500
501static inline
502bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
503 struct mutex_waiter *waiter)
504{
505 struct ww_mutex *ww;
506
507 ww = container_of(lock, struct ww_mutex, base);
508
509 /*
510 * If ww->ctx is set the contents are undefined, only
511 * by acquiring wait_lock there is a guarantee that
512 * they are not invalid when reading.
513 *
514 * As such, when deadlock detection needs to be
515 * performed the optimistic spinning cannot be done.
516 *
517 * Check this in every inner iteration because we may
518 * be racing against another thread's ww_mutex_lock.
519 */
520 if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
521 return false;
522
523 /*
524 * If we aren't on the wait list yet, cancel the spin
525 * if there are waiters. We want to avoid stealing the
526 * lock from a waiter with an earlier stamp, since the
527 * other thread may already own a lock that we also
528 * need.
529 */
530 if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
531 return false;
532
533 /*
534 * Similarly, stop spinning if we are no longer the
535 * first waiter.
536 */
537 if (waiter && !__mutex_waiter_is_first(lock, waiter))
538 return false;
539
540 return true;
541}
542
543/*
544 * Look out! "owner" is an entirely speculative pointer access and not
545 * reliable.
546 *
547 * "noinline" so that this function shows up on perf profiles.
548 */
549static noinline
550bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
551 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
552{
553 bool ret = true;
554
555 rcu_read_lock();
556 while (__mutex_owner(lock) == owner) {
557 /*
558 * Ensure we emit the owner->on_cpu, dereference _after_
559 * checking lock->owner still matches owner. If that fails,
560 * owner might point to freed memory. If it still matches,
561 * the rcu_read_lock() ensures the memory stays valid.
562 */
563 barrier();
564
565 /*
566 * Use vcpu_is_preempted to detect lock holder preemption issue.
567 */
568 if (!owner->on_cpu || need_resched() ||
569 vcpu_is_preempted(task_cpu(owner))) {
570 ret = false;
571 break;
572 }
573
574 if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
575 ret = false;
576 break;
577 }
578
579 cpu_relax();
580 }
581 rcu_read_unlock();
582
583 return ret;
584}
585
586/*
587 * Initial check for entering the mutex spinning loop
588 */
589static inline int mutex_can_spin_on_owner(struct mutex *lock)
590{
591 struct task_struct *owner;
592 int retval = 1;
593
594 if (need_resched())
595 return 0;
596
597 rcu_read_lock();
598 owner = __mutex_owner(lock);
599
600 /*
601 * As lock holder preemption issue, we both skip spinning if task is not
602 * on cpu or its cpu is preempted
603 */
604 if (owner)
605 retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
606 rcu_read_unlock();
607
608 /*
609 * If lock->owner is not set, the mutex has been released. Return true
610 * such that we'll trylock in the spin path, which is a faster option
611 * than the blocking slow path.
612 */
613 return retval;
614}
615
616/*
617 * Optimistic spinning.
618 *
619 * We try to spin for acquisition when we find that the lock owner
620 * is currently running on a (different) CPU and while we don't
621 * need to reschedule. The rationale is that if the lock owner is
622 * running, it is likely to release the lock soon.
623 *
624 * The mutex spinners are queued up using MCS lock so that only one
625 * spinner can compete for the mutex. However, if mutex spinning isn't
626 * going to happen, there is no point in going through the lock/unlock
627 * overhead.
628 *
629 * Returns true when the lock was taken, otherwise false, indicating
630 * that we need to jump to the slowpath and sleep.
631 *
632 * The waiter flag is set to true if the spinner is a waiter in the wait
633 * queue. The waiter-spinner will spin on the lock directly and concurrently
634 * with the spinner at the head of the OSQ, if present, until the owner is
635 * changed to itself.
636 */
637static __always_inline bool
638mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
639 const bool use_ww_ctx, struct mutex_waiter *waiter)
640{
641 if (!waiter) {
642 /*
643 * The purpose of the mutex_can_spin_on_owner() function is
644 * to eliminate the overhead of osq_lock() and osq_unlock()
645 * in case spinning isn't possible. As a waiter-spinner
646 * is not going to take OSQ lock anyway, there is no need
647 * to call mutex_can_spin_on_owner().
648 */
649 if (!mutex_can_spin_on_owner(lock))
650 goto fail;
651
652 /*
653 * In order to avoid a stampede of mutex spinners trying to
654 * acquire the mutex all at once, the spinners need to take a
655 * MCS (queued) lock first before spinning on the owner field.
656 */
657 if (!osq_lock(&lock->osq))
658 goto fail;
659 }
660
661 for (;;) {
662 struct task_struct *owner;
663
664 /* Try to acquire the mutex... */
665 owner = __mutex_trylock_or_owner(lock);
666 if (!owner)
667 break;
668
669 /*
670 * There's an owner, wait for it to either
671 * release the lock or go to sleep.
672 */
673 if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
674 goto fail_unlock;
675
676 /*
677 * The cpu_relax() call is a compiler barrier which forces
678 * everything in this loop to be re-loaded. We don't need
679 * memory barriers as we'll eventually observe the right
680 * values at the cost of a few extra spins.
681 */
682 cpu_relax();
683 }
684
685 if (!waiter)
686 osq_unlock(&lock->osq);
687
688 return true;
689
690
691fail_unlock:
692 if (!waiter)
693 osq_unlock(&lock->osq);
694
695fail:
696 /*
697 * If we fell out of the spin path because of need_resched(),
698 * reschedule now, before we try-lock the mutex. This avoids getting
699 * scheduled out right after we obtained the mutex.
700 */
701 if (need_resched()) {
702 /*
703 * We _should_ have TASK_RUNNING here, but just in case
704 * we do not, make it so, otherwise we might get stuck.
705 */
706 __set_current_state(TASK_RUNNING);
707 schedule_preempt_disabled();
708 }
709
710 return false;
711}
712#else
713static __always_inline bool
714mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
715 const bool use_ww_ctx, struct mutex_waiter *waiter)
716{
717 return false;
718}
719#endif
720
721static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
722
723/**
724 * mutex_unlock - release the mutex
725 * @lock: the mutex to be released
726 *
727 * Unlock a mutex that has been locked by this task previously.
728 *
729 * This function must not be used in interrupt context. Unlocking
730 * of a not locked mutex is not allowed.
731 *
732 * This function is similar to (but not equivalent to) up().
733 */
734void __sched mutex_unlock(struct mutex *lock)
735{
736#ifndef CONFIG_DEBUG_LOCK_ALLOC
737 if (__mutex_unlock_fast(lock))
738 return;
739#endif
740 __mutex_unlock_slowpath(lock, _RET_IP_);
741}
742EXPORT_SYMBOL(mutex_unlock);
743
744/**
745 * ww_mutex_unlock - release the w/w mutex
746 * @lock: the mutex to be released
747 *
748 * Unlock a mutex that has been locked by this task previously with any of the
749 * ww_mutex_lock* functions (with or without an acquire context). It is
750 * forbidden to release the locks after releasing the acquire context.
751 *
752 * This function must not be used in interrupt context. Unlocking
753 * of a unlocked mutex is not allowed.
754 */
755void __sched ww_mutex_unlock(struct ww_mutex *lock)
756{
757 /*
758 * The unlocking fastpath is the 0->1 transition from 'locked'
759 * into 'unlocked' state:
760 */
761 if (lock->ctx) {
762#ifdef CONFIG_DEBUG_MUTEXES
763 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
764#endif
765 if (lock->ctx->acquired > 0)
766 lock->ctx->acquired--;
767 lock->ctx = NULL;
768 }
769
770 mutex_unlock(&lock->base);
771}
772EXPORT_SYMBOL(ww_mutex_unlock);
773
774
775static __always_inline int __sched
776__ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
777{
778 if (ww_ctx->acquired > 0) {
779#ifdef CONFIG_DEBUG_MUTEXES
780 struct ww_mutex *ww;
781
782 ww = container_of(lock, struct ww_mutex, base);
783 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
784 ww_ctx->contending_lock = ww;
785#endif
786 return -EDEADLK;
787 }
788
789 return 0;
790}
791
792
793/*
794 * Check the wound condition for the current lock acquire.
795 *
796 * Wound-Wait: If we're wounded, kill ourself.
797 *
798 * Wait-Die: If we're trying to acquire a lock already held by an older
799 * context, kill ourselves.
800 *
801 * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
802 * look at waiters before us in the wait-list.
803 */
804static inline int __sched
805__ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
806 struct ww_acquire_ctx *ctx)
807{
808 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
809 struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
810 struct mutex_waiter *cur;
811
812 if (ctx->acquired == 0)
813 return 0;
814
815 if (!ctx->is_wait_die) {
816 if (ctx->wounded)
817 return __ww_mutex_kill(lock, ctx);
818
819 return 0;
820 }
821
822 if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
823 return __ww_mutex_kill(lock, ctx);
824
825 /*
826 * If there is a waiter in front of us that has a context, then its
827 * stamp is earlier than ours and we must kill ourself.
828 */
829 cur = waiter;
830 list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
831 if (!cur->ww_ctx)
832 continue;
833
834 return __ww_mutex_kill(lock, ctx);
835 }
836
837 return 0;
838}
839
840/*
841 * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
842 * first. Such that older contexts are preferred to acquire the lock over
843 * younger contexts.
844 *
845 * Waiters without context are interspersed in FIFO order.
846 *
847 * Furthermore, for Wait-Die kill ourself immediately when possible (there are
848 * older contexts already waiting) to avoid unnecessary waiting and for
849 * Wound-Wait ensure we wound the owning context when it is younger.
850 */
851static inline int __sched
852__ww_mutex_add_waiter(struct mutex_waiter *waiter,
853 struct mutex *lock,
854 struct ww_acquire_ctx *ww_ctx)
855{
856 struct mutex_waiter *cur;
857 struct list_head *pos;
858 bool is_wait_die;
859
860 if (!ww_ctx) {
861 __mutex_add_waiter(lock, waiter, &lock->wait_list);
862 return 0;
863 }
864
865 is_wait_die = ww_ctx->is_wait_die;
866
867 /*
868 * Add the waiter before the first waiter with a higher stamp.
869 * Waiters without a context are skipped to avoid starving
870 * them. Wait-Die waiters may die here. Wound-Wait waiters
871 * never die here, but they are sorted in stamp order and
872 * may wound the lock holder.
873 */
874 pos = &lock->wait_list;
875 list_for_each_entry_reverse(cur, &lock->wait_list, list) {
876 if (!cur->ww_ctx)
877 continue;
878
879 if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
880 /*
881 * Wait-Die: if we find an older context waiting, there
882 * is no point in queueing behind it, as we'd have to
883 * die the moment it would acquire the lock.
884 */
885 if (is_wait_die) {
886 int ret = __ww_mutex_kill(lock, ww_ctx);
887
888 if (ret)
889 return ret;
890 }
891
892 break;
893 }
894
895 pos = &cur->list;
896
897 /* Wait-Die: ensure younger waiters die. */
898 __ww_mutex_die(lock, cur, ww_ctx);
899 }
900
901 __mutex_add_waiter(lock, waiter, pos);
902
903 /*
904 * Wound-Wait: if we're blocking on a mutex owned by a younger context,
905 * wound that such that we might proceed.
906 */
907 if (!is_wait_die) {
908 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
909
910 /*
911 * See ww_mutex_set_context_fastpath(). Orders setting
912 * MUTEX_FLAG_WAITERS vs the ww->ctx load,
913 * such that either we or the fastpath will wound @ww->ctx.
914 */
915 smp_mb();
916 __ww_mutex_wound(lock, ww_ctx, ww->ctx);
917 }
918
919 return 0;
920}
921
922/*
923 * Lock a mutex (possibly interruptible), slowpath:
924 */
925static __always_inline int __sched
926__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
927 struct lockdep_map *nest_lock, unsigned long ip,
928 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
929{
930 struct mutex_waiter waiter;
931 bool first = false;
932 struct ww_mutex *ww;
933 int ret;
934
935 might_sleep();
936
937#ifdef CONFIG_DEBUG_MUTEXES
938 DEBUG_LOCKS_WARN_ON(lock->magic != lock);
939#endif
940
941 ww = container_of(lock, struct ww_mutex, base);
942 if (use_ww_ctx && ww_ctx) {
943 if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
944 return -EALREADY;
945
946 /*
947 * Reset the wounded flag after a kill. No other process can
948 * race and wound us here since they can't have a valid owner
949 * pointer if we don't have any locks held.
950 */
951 if (ww_ctx->acquired == 0)
952 ww_ctx->wounded = 0;
953 }
954
955 preempt_disable();
956 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
957
958 if (__mutex_trylock(lock) ||
959 mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
960 /* got the lock, yay! */
961 lock_acquired(&lock->dep_map, ip);
962 if (use_ww_ctx && ww_ctx)
963 ww_mutex_set_context_fastpath(ww, ww_ctx);
964 preempt_enable();
965 return 0;
966 }
967
968 spin_lock(&lock->wait_lock);
969 /*
970 * After waiting to acquire the wait_lock, try again.
971 */
972 if (__mutex_trylock(lock)) {
973 if (use_ww_ctx && ww_ctx)
974 __ww_mutex_check_waiters(lock, ww_ctx);
975
976 goto skip_wait;
977 }
978
979 debug_mutex_lock_common(lock, &waiter);
980
981 lock_contended(&lock->dep_map, ip);
982
983 if (!use_ww_ctx) {
984 /* add waiting tasks to the end of the waitqueue (FIFO): */
985 __mutex_add_waiter(lock, &waiter, &lock->wait_list);
986
987
988#ifdef CONFIG_DEBUG_MUTEXES
989 waiter.ww_ctx = MUTEX_POISON_WW_CTX;
990#endif
991 } else {
992 /*
993 * Add in stamp order, waking up waiters that must kill
994 * themselves.
995 */
996 ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
997 if (ret)
998 goto err_early_kill;
999
1000 waiter.ww_ctx = ww_ctx;
1001 }
1002
1003 waiter.task = current;
1004
1005 set_current_state(state);
1006 for (;;) {
1007 /*
1008 * Once we hold wait_lock, we're serialized against
1009 * mutex_unlock() handing the lock off to us, do a trylock
1010 * before testing the error conditions to make sure we pick up
1011 * the handoff.
1012 */
1013 if (__mutex_trylock(lock))
1014 goto acquired;
1015
1016 /*
1017 * Check for signals and kill conditions while holding
1018 * wait_lock. This ensures the lock cancellation is ordered
1019 * against mutex_unlock() and wake-ups do not go missing.
1020 */
1021 if (signal_pending_state(state, current)) {
1022 ret = -EINTR;
1023 goto err;
1024 }
1025
1026 if (use_ww_ctx && ww_ctx) {
1027 ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
1028 if (ret)
1029 goto err;
1030 }
1031
1032 spin_unlock(&lock->wait_lock);
1033 schedule_preempt_disabled();
1034
1035 /*
1036 * ww_mutex needs to always recheck its position since its waiter
1037 * list is not FIFO ordered.
1038 */
1039 if ((use_ww_ctx && ww_ctx) || !first) {
1040 first = __mutex_waiter_is_first(lock, &waiter);
1041 if (first)
1042 __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
1043 }
1044
1045 set_current_state(state);
1046 /*
1047 * Here we order against unlock; we must either see it change
1048 * state back to RUNNING and fall through the next schedule(),
1049 * or we must see its unlock and acquire.
1050 */
1051 if (__mutex_trylock(lock) ||
1052 (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
1053 break;
1054
1055 spin_lock(&lock->wait_lock);
1056 }
1057 spin_lock(&lock->wait_lock);
1058acquired:
1059 __set_current_state(TASK_RUNNING);
1060
1061 if (use_ww_ctx && ww_ctx) {
1062 /*
1063 * Wound-Wait; we stole the lock (!first_waiter), check the
1064 * waiters as anyone might want to wound us.
1065 */
1066 if (!ww_ctx->is_wait_die &&
1067 !__mutex_waiter_is_first(lock, &waiter))
1068 __ww_mutex_check_waiters(lock, ww_ctx);
1069 }
1070
1071 mutex_remove_waiter(lock, &waiter, current);
1072 if (likely(list_empty(&lock->wait_list)))
1073 __mutex_clear_flag(lock, MUTEX_FLAGS);
1074
1075 debug_mutex_free_waiter(&waiter);
1076
1077skip_wait:
1078 /* got the lock - cleanup and rejoice! */
1079 lock_acquired(&lock->dep_map, ip);
1080
1081 if (use_ww_ctx && ww_ctx)
1082 ww_mutex_lock_acquired(ww, ww_ctx);
1083
1084 spin_unlock(&lock->wait_lock);
1085 preempt_enable();
1086 return 0;
1087
1088err:
1089 __set_current_state(TASK_RUNNING);
1090 mutex_remove_waiter(lock, &waiter, current);
1091err_early_kill:
1092 spin_unlock(&lock->wait_lock);
1093 debug_mutex_free_waiter(&waiter);
1094 mutex_release(&lock->dep_map, ip);
1095 preempt_enable();
1096 return ret;
1097}
1098
1099static int __sched
1100__mutex_lock(struct mutex *lock, long state, unsigned int subclass,
1101 struct lockdep_map *nest_lock, unsigned long ip)
1102{
1103 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
1104}
1105
1106static int __sched
1107__ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
1108 struct lockdep_map *nest_lock, unsigned long ip,
1109 struct ww_acquire_ctx *ww_ctx)
1110{
1111 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
1112}
1113
1114#ifdef CONFIG_DEBUG_LOCK_ALLOC
1115void __sched
1116mutex_lock_nested(struct mutex *lock, unsigned int subclass)
1117{
1118 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
1119}
1120
1121EXPORT_SYMBOL_GPL(mutex_lock_nested);
1122
1123void __sched
1124_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
1125{
1126 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
1127}
1128EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
1129
1130int __sched
1131mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
1132{
1133 return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
1134}
1135EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
1136
1137int __sched
1138mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
1139{
1140 return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
1141}
1142EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
1143
1144void __sched
1145mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
1146{
1147 int token;
1148
1149 might_sleep();
1150
1151 token = io_schedule_prepare();
1152 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
1153 subclass, NULL, _RET_IP_, NULL, 0);
1154 io_schedule_finish(token);
1155}
1156EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
1157
1158static inline int
1159ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1160{
1161#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
1162 unsigned tmp;
1163
1164 if (ctx->deadlock_inject_countdown-- == 0) {
1165 tmp = ctx->deadlock_inject_interval;
1166 if (tmp > UINT_MAX/4)
1167 tmp = UINT_MAX;
1168 else
1169 tmp = tmp*2 + tmp + tmp/2;
1170
1171 ctx->deadlock_inject_interval = tmp;
1172 ctx->deadlock_inject_countdown = tmp;
1173 ctx->contending_lock = lock;
1174
1175 ww_mutex_unlock(lock);
1176
1177 return -EDEADLK;
1178 }
1179#endif
1180
1181 return 0;
1182}
1183
1184int __sched
1185ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1186{
1187 int ret;
1188
1189 might_sleep();
1190 ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
1191 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
1192 ctx);
1193 if (!ret && ctx && ctx->acquired > 1)
1194 return ww_mutex_deadlock_injection(lock, ctx);
1195
1196 return ret;
1197}
1198EXPORT_SYMBOL_GPL(ww_mutex_lock);
1199
1200int __sched
1201ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1202{
1203 int ret;
1204
1205 might_sleep();
1206 ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
1207 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
1208 ctx);
1209
1210 if (!ret && ctx && ctx->acquired > 1)
1211 return ww_mutex_deadlock_injection(lock, ctx);
1212
1213 return ret;
1214}
1215EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
1216
1217#endif
1218
1219/*
1220 * Release the lock, slowpath:
1221 */
1222static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
1223{
1224 struct task_struct *next = NULL;
1225 DEFINE_WAKE_Q(wake_q);
1226 unsigned long owner;
1227
1228 mutex_release(&lock->dep_map, ip);
1229
1230 /*
1231 * Release the lock before (potentially) taking the spinlock such that
1232 * other contenders can get on with things ASAP.
1233 *
1234 * Except when HANDOFF, in that case we must not clear the owner field,
1235 * but instead set it to the top waiter.
1236 */
1237 owner = atomic_long_read(&lock->owner);
1238 for (;;) {
1239 unsigned long old;
1240
1241#ifdef CONFIG_DEBUG_MUTEXES
1242 DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
1243 DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
1244#endif
1245
1246 if (owner & MUTEX_FLAG_HANDOFF)
1247 break;
1248
1249 old = atomic_long_cmpxchg_release(&lock->owner, owner,
1250 __owner_flags(owner));
1251 if (old == owner) {
1252 if (owner & MUTEX_FLAG_WAITERS)
1253 break;
1254
1255 return;
1256 }
1257
1258 owner = old;
1259 }
1260
1261 spin_lock(&lock->wait_lock);
1262 debug_mutex_unlock(lock);
1263 if (!list_empty(&lock->wait_list)) {
1264 /* get the first entry from the wait-list: */
1265 struct mutex_waiter *waiter =
1266 list_first_entry(&lock->wait_list,
1267 struct mutex_waiter, list);
1268
1269 next = waiter->task;
1270
1271 debug_mutex_wake_waiter(lock, waiter);
1272 wake_q_add(&wake_q, next);
1273 }
1274
1275 if (owner & MUTEX_FLAG_HANDOFF)
1276 __mutex_handoff(lock, next);
1277
1278 spin_unlock(&lock->wait_lock);
1279
1280 wake_up_q(&wake_q);
1281}
1282
1283#ifndef CONFIG_DEBUG_LOCK_ALLOC
1284/*
1285 * Here come the less common (and hence less performance-critical) APIs:
1286 * mutex_lock_interruptible() and mutex_trylock().
1287 */
1288static noinline int __sched
1289__mutex_lock_killable_slowpath(struct mutex *lock);
1290
1291static noinline int __sched
1292__mutex_lock_interruptible_slowpath(struct mutex *lock);
1293
1294/**
1295 * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
1296 * @lock: The mutex to be acquired.
1297 *
1298 * Lock the mutex like mutex_lock(). If a signal is delivered while the
1299 * process is sleeping, this function will return without acquiring the
1300 * mutex.
1301 *
1302 * Context: Process context.
1303 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1304 * signal arrived.
1305 */
1306int __sched mutex_lock_interruptible(struct mutex *lock)
1307{
1308 might_sleep();
1309
1310 if (__mutex_trylock_fast(lock))
1311 return 0;
1312
1313 return __mutex_lock_interruptible_slowpath(lock);
1314}
1315
1316EXPORT_SYMBOL(mutex_lock_interruptible);
1317
1318/**
1319 * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
1320 * @lock: The mutex to be acquired.
1321 *
1322 * Lock the mutex like mutex_lock(). If a signal which will be fatal to
1323 * the current process is delivered while the process is sleeping, this
1324 * function will return without acquiring the mutex.
1325 *
1326 * Context: Process context.
1327 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1328 * fatal signal arrived.
1329 */
1330int __sched mutex_lock_killable(struct mutex *lock)
1331{
1332 might_sleep();
1333
1334 if (__mutex_trylock_fast(lock))
1335 return 0;
1336
1337 return __mutex_lock_killable_slowpath(lock);
1338}
1339EXPORT_SYMBOL(mutex_lock_killable);
1340
1341/**
1342 * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1343 * @lock: The mutex to be acquired.
1344 *
1345 * Lock the mutex like mutex_lock(). While the task is waiting for this
1346 * mutex, it will be accounted as being in the IO wait state by the
1347 * scheduler.
1348 *
1349 * Context: Process context.
1350 */
1351void __sched mutex_lock_io(struct mutex *lock)
1352{
1353 int token;
1354
1355 token = io_schedule_prepare();
1356 mutex_lock(lock);
1357 io_schedule_finish(token);
1358}
1359EXPORT_SYMBOL_GPL(mutex_lock_io);
1360
1361static noinline void __sched
1362__mutex_lock_slowpath(struct mutex *lock)
1363{
1364 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1365}
1366
1367static noinline int __sched
1368__mutex_lock_killable_slowpath(struct mutex *lock)
1369{
1370 return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1371}
1372
1373static noinline int __sched
1374__mutex_lock_interruptible_slowpath(struct mutex *lock)
1375{
1376 return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1377}
1378
1379static noinline int __sched
1380__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1381{
1382 return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
1383 _RET_IP_, ctx);
1384}
1385
1386static noinline int __sched
1387__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1388 struct ww_acquire_ctx *ctx)
1389{
1390 return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
1391 _RET_IP_, ctx);
1392}
1393
1394#endif
1395
1396/**
1397 * mutex_trylock - try to acquire the mutex, without waiting
1398 * @lock: the mutex to be acquired
1399 *
1400 * Try to acquire the mutex atomically. Returns 1 if the mutex
1401 * has been acquired successfully, and 0 on contention.
1402 *
1403 * NOTE: this function follows the spin_trylock() convention, so
1404 * it is negated from the down_trylock() return values! Be careful
1405 * about this when converting semaphore users to mutexes.
1406 *
1407 * This function must not be used in interrupt context. The
1408 * mutex must be released by the same task that acquired it.
1409 */
1410int __sched mutex_trylock(struct mutex *lock)
1411{
1412 bool locked;
1413
1414#ifdef CONFIG_DEBUG_MUTEXES
1415 DEBUG_LOCKS_WARN_ON(lock->magic != lock);
1416#endif
1417
1418 locked = __mutex_trylock(lock);
1419 if (locked)
1420 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1421
1422 return locked;
1423}
1424EXPORT_SYMBOL(mutex_trylock);
1425
1426#ifndef CONFIG_DEBUG_LOCK_ALLOC
1427int __sched
1428ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1429{
1430 might_sleep();
1431
1432 if (__mutex_trylock_fast(&lock->base)) {
1433 if (ctx)
1434 ww_mutex_set_context_fastpath(lock, ctx);
1435 return 0;
1436 }
1437
1438 return __ww_mutex_lock_slowpath(lock, ctx);
1439}
1440EXPORT_SYMBOL(ww_mutex_lock);
1441
1442int __sched
1443ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1444{
1445 might_sleep();
1446
1447 if (__mutex_trylock_fast(&lock->base)) {
1448 if (ctx)
1449 ww_mutex_set_context_fastpath(lock, ctx);
1450 return 0;
1451 }
1452
1453 return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1454}
1455EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1456
1457#endif
1458
1459/**
1460 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1461 * @cnt: the atomic which we are to dec
1462 * @lock: the mutex to return holding if we dec to 0
1463 *
1464 * return true and hold lock if we dec to 0, return false otherwise
1465 */
1466int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1467{
1468 /* dec if we can't possibly hit 0 */
1469 if (atomic_add_unless(cnt, -1, 1))
1470 return 0;
1471 /* we might hit 0, so take the lock */
1472 mutex_lock(lock);
1473 if (!atomic_dec_and_test(cnt)) {
1474 /* when we actually did the dec, we didn't hit 0 */
1475 mutex_unlock(lock);
1476 return 0;
1477 }
1478 /* we hit 0, and we hold the lock */
1479 return 1;
1480}
1481EXPORT_SYMBOL(atomic_dec_and_mutex_lock);