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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * kernel/locking/mutex.c
4 *
5 * Mutexes: blocking mutual exclusion locks
6 *
7 * Started by Ingo Molnar:
8 *
9 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <[email protected]>
10 *
11 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
12 * David Howells for suggestions and improvements.
13 *
14 * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
15 * from the -rt tree, where it was originally implemented for rtmutexes
16 * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
17 * and Sven Dietrich.
18 *
19 * Also see Documentation/locking/mutex-design.rst.
20 */
21#include <linux/mutex.h>
22#include <linux/ww_mutex.h>
23#include <linux/sched/signal.h>
24#include <linux/sched/rt.h>
25#include <linux/sched/wake_q.h>
26#include <linux/sched/debug.h>
27#include <linux/export.h>
28#include <linux/spinlock.h>
29#include <linux/interrupt.h>
30#include <linux/debug_locks.h>
31#include <linux/osq_lock.h>
32
33#ifndef CONFIG_PREEMPT_RT
34#include "mutex.h"
35
36#ifdef CONFIG_DEBUG_MUTEXES
37# define MUTEX_WARN_ON(cond) DEBUG_LOCKS_WARN_ON(cond)
38#else
39# define MUTEX_WARN_ON(cond)
40#endif
41
42void
43__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
44{
45 atomic_long_set(&lock->owner, 0);
46 raw_spin_lock_init(&lock->wait_lock);
47 INIT_LIST_HEAD(&lock->wait_list);
48#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
49 osq_lock_init(&lock->osq);
50#endif
51
52 debug_mutex_init(lock, name, key);
53}
54EXPORT_SYMBOL(__mutex_init);
55
56/*
57 * @owner: contains: 'struct task_struct *' to the current lock owner,
58 * NULL means not owned. Since task_struct pointers are aligned at
59 * at least L1_CACHE_BYTES, we have low bits to store extra state.
60 *
61 * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
62 * Bit1 indicates unlock needs to hand the lock to the top-waiter
63 * Bit2 indicates handoff has been done and we're waiting for pickup.
64 */
65#define MUTEX_FLAG_WAITERS 0x01
66#define MUTEX_FLAG_HANDOFF 0x02
67#define MUTEX_FLAG_PICKUP 0x04
68
69#define MUTEX_FLAGS 0x07
70
71/*
72 * Internal helper function; C doesn't allow us to hide it :/
73 *
74 * DO NOT USE (outside of mutex code).
75 */
76static inline struct task_struct *__mutex_owner(struct mutex *lock)
77{
78 return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
79}
80
81static inline struct task_struct *__owner_task(unsigned long owner)
82{
83 return (struct task_struct *)(owner & ~MUTEX_FLAGS);
84}
85
86bool mutex_is_locked(struct mutex *lock)
87{
88 return __mutex_owner(lock) != NULL;
89}
90EXPORT_SYMBOL(mutex_is_locked);
91
92static inline unsigned long __owner_flags(unsigned long owner)
93{
94 return owner & MUTEX_FLAGS;
95}
96
97/*
98 * Returns: __mutex_owner(lock) on failure or NULL on success.
99 */
100static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff)
101{
102 unsigned long owner, curr = (unsigned long)current;
103
104 owner = atomic_long_read(&lock->owner);
105 for (;;) { /* must loop, can race against a flag */
106 unsigned long flags = __owner_flags(owner);
107 unsigned long task = owner & ~MUTEX_FLAGS;
108
109 if (task) {
110 if (flags & MUTEX_FLAG_PICKUP) {
111 if (task != curr)
112 break;
113 flags &= ~MUTEX_FLAG_PICKUP;
114 } else if (handoff) {
115 if (flags & MUTEX_FLAG_HANDOFF)
116 break;
117 flags |= MUTEX_FLAG_HANDOFF;
118 } else {
119 break;
120 }
121 } else {
122 MUTEX_WARN_ON(flags & (MUTEX_FLAG_HANDOFF | MUTEX_FLAG_PICKUP));
123 task = curr;
124 }
125
126 if (atomic_long_try_cmpxchg_acquire(&lock->owner, &owner, task | flags)) {
127 if (task == curr)
128 return NULL;
129 break;
130 }
131 }
132
133 return __owner_task(owner);
134}
135
136/*
137 * Trylock or set HANDOFF
138 */
139static inline bool __mutex_trylock_or_handoff(struct mutex *lock, bool handoff)
140{
141 return !__mutex_trylock_common(lock, handoff);
142}
143
144/*
145 * Actual trylock that will work on any unlocked state.
146 */
147static inline bool __mutex_trylock(struct mutex *lock)
148{
149 return !__mutex_trylock_common(lock, false);
150}
151
152#ifndef CONFIG_DEBUG_LOCK_ALLOC
153/*
154 * Lockdep annotations are contained to the slow paths for simplicity.
155 * There is nothing that would stop spreading the lockdep annotations outwards
156 * except more code.
157 */
158
159/*
160 * Optimistic trylock that only works in the uncontended case. Make sure to
161 * follow with a __mutex_trylock() before failing.
162 */
163static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
164{
165 unsigned long curr = (unsigned long)current;
166 unsigned long zero = 0UL;
167
168 if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
169 return true;
170
171 return false;
172}
173
174static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
175{
176 unsigned long curr = (unsigned long)current;
177
178 return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
179}
180#endif
181
182static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
183{
184 atomic_long_or(flag, &lock->owner);
185}
186
187static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
188{
189 atomic_long_andnot(flag, &lock->owner);
190}
191
192static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
193{
194 return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
195}
196
197/*
198 * Add @waiter to a given location in the lock wait_list and set the
199 * FLAG_WAITERS flag if it's the first waiter.
200 */
201static void
202__mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
203 struct list_head *list)
204{
205 debug_mutex_add_waiter(lock, waiter, current);
206
207 list_add_tail(&waiter->list, list);
208 if (__mutex_waiter_is_first(lock, waiter))
209 __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
210}
211
212static void
213__mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter)
214{
215 list_del(&waiter->list);
216 if (likely(list_empty(&lock->wait_list)))
217 __mutex_clear_flag(lock, MUTEX_FLAGS);
218
219 debug_mutex_remove_waiter(lock, waiter, current);
220}
221
222/*
223 * Give up ownership to a specific task, when @task = NULL, this is equivalent
224 * to a regular unlock. Sets PICKUP on a handoff, clears HANDOFF, preserves
225 * WAITERS. Provides RELEASE semantics like a regular unlock, the
226 * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
227 */
228static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
229{
230 unsigned long owner = atomic_long_read(&lock->owner);
231
232 for (;;) {
233 unsigned long new;
234
235 MUTEX_WARN_ON(__owner_task(owner) != current);
236 MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
237
238 new = (owner & MUTEX_FLAG_WAITERS);
239 new |= (unsigned long)task;
240 if (task)
241 new |= MUTEX_FLAG_PICKUP;
242
243 if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, new))
244 break;
245 }
246}
247
248#ifndef CONFIG_DEBUG_LOCK_ALLOC
249/*
250 * We split the mutex lock/unlock logic into separate fastpath and
251 * slowpath functions, to reduce the register pressure on the fastpath.
252 * We also put the fastpath first in the kernel image, to make sure the
253 * branch is predicted by the CPU as default-untaken.
254 */
255static void __sched __mutex_lock_slowpath(struct mutex *lock);
256
257/**
258 * mutex_lock - acquire the mutex
259 * @lock: the mutex to be acquired
260 *
261 * Lock the mutex exclusively for this task. If the mutex is not
262 * available right now, it will sleep until it can get it.
263 *
264 * The mutex must later on be released by the same task that
265 * acquired it. Recursive locking is not allowed. The task
266 * may not exit without first unlocking the mutex. Also, kernel
267 * memory where the mutex resides must not be freed with
268 * the mutex still locked. The mutex must first be initialized
269 * (or statically defined) before it can be locked. memset()-ing
270 * the mutex to 0 is not allowed.
271 *
272 * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
273 * checks that will enforce the restrictions and will also do
274 * deadlock debugging)
275 *
276 * This function is similar to (but not equivalent to) down().
277 */
278void __sched mutex_lock(struct mutex *lock)
279{
280 might_sleep();
281
282 if (!__mutex_trylock_fast(lock))
283 __mutex_lock_slowpath(lock);
284}
285EXPORT_SYMBOL(mutex_lock);
286#endif
287
288#include "ww_mutex.h"
289
290#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
291
292/*
293 * Trylock variant that returns the owning task on failure.
294 */
295static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
296{
297 return __mutex_trylock_common(lock, false);
298}
299
300static inline
301bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
302 struct mutex_waiter *waiter)
303{
304 struct ww_mutex *ww;
305
306 ww = container_of(lock, struct ww_mutex, base);
307
308 /*
309 * If ww->ctx is set the contents are undefined, only
310 * by acquiring wait_lock there is a guarantee that
311 * they are not invalid when reading.
312 *
313 * As such, when deadlock detection needs to be
314 * performed the optimistic spinning cannot be done.
315 *
316 * Check this in every inner iteration because we may
317 * be racing against another thread's ww_mutex_lock.
318 */
319 if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
320 return false;
321
322 /*
323 * If we aren't on the wait list yet, cancel the spin
324 * if there are waiters. We want to avoid stealing the
325 * lock from a waiter with an earlier stamp, since the
326 * other thread may already own a lock that we also
327 * need.
328 */
329 if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
330 return false;
331
332 /*
333 * Similarly, stop spinning if we are no longer the
334 * first waiter.
335 */
336 if (waiter && !__mutex_waiter_is_first(lock, waiter))
337 return false;
338
339 return true;
340}
341
342/*
343 * Look out! "owner" is an entirely speculative pointer access and not
344 * reliable.
345 *
346 * "noinline" so that this function shows up on perf profiles.
347 */
348static noinline
349bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
350 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
351{
352 bool ret = true;
353
354 lockdep_assert_preemption_disabled();
355
356 while (__mutex_owner(lock) == owner) {
357 /*
358 * Ensure we emit the owner->on_cpu, dereference _after_
359 * checking lock->owner still matches owner. And we already
360 * disabled preemption which is equal to the RCU read-side
361 * crital section in optimistic spinning code. Thus the
362 * task_strcut structure won't go away during the spinning
363 * period
364 */
365 barrier();
366
367 /*
368 * Use vcpu_is_preempted to detect lock holder preemption issue.
369 */
370 if (!owner_on_cpu(owner) || need_resched()) {
371 ret = false;
372 break;
373 }
374
375 if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
376 ret = false;
377 break;
378 }
379
380 cpu_relax();
381 }
382
383 return ret;
384}
385
386/*
387 * Initial check for entering the mutex spinning loop
388 */
389static inline int mutex_can_spin_on_owner(struct mutex *lock)
390{
391 struct task_struct *owner;
392 int retval = 1;
393
394 lockdep_assert_preemption_disabled();
395
396 if (need_resched())
397 return 0;
398
399 /*
400 * We already disabled preemption which is equal to the RCU read-side
401 * crital section in optimistic spinning code. Thus the task_strcut
402 * structure won't go away during the spinning period.
403 */
404 owner = __mutex_owner(lock);
405 if (owner)
406 retval = owner_on_cpu(owner);
407
408 /*
409 * If lock->owner is not set, the mutex has been released. Return true
410 * such that we'll trylock in the spin path, which is a faster option
411 * than the blocking slow path.
412 */
413 return retval;
414}
415
416/*
417 * Optimistic spinning.
418 *
419 * We try to spin for acquisition when we find that the lock owner
420 * is currently running on a (different) CPU and while we don't
421 * need to reschedule. The rationale is that if the lock owner is
422 * running, it is likely to release the lock soon.
423 *
424 * The mutex spinners are queued up using MCS lock so that only one
425 * spinner can compete for the mutex. However, if mutex spinning isn't
426 * going to happen, there is no point in going through the lock/unlock
427 * overhead.
428 *
429 * Returns true when the lock was taken, otherwise false, indicating
430 * that we need to jump to the slowpath and sleep.
431 *
432 * The waiter flag is set to true if the spinner is a waiter in the wait
433 * queue. The waiter-spinner will spin on the lock directly and concurrently
434 * with the spinner at the head of the OSQ, if present, until the owner is
435 * changed to itself.
436 */
437static __always_inline bool
438mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
439 struct mutex_waiter *waiter)
440{
441 if (!waiter) {
442 /*
443 * The purpose of the mutex_can_spin_on_owner() function is
444 * to eliminate the overhead of osq_lock() and osq_unlock()
445 * in case spinning isn't possible. As a waiter-spinner
446 * is not going to take OSQ lock anyway, there is no need
447 * to call mutex_can_spin_on_owner().
448 */
449 if (!mutex_can_spin_on_owner(lock))
450 goto fail;
451
452 /*
453 * In order to avoid a stampede of mutex spinners trying to
454 * acquire the mutex all at once, the spinners need to take a
455 * MCS (queued) lock first before spinning on the owner field.
456 */
457 if (!osq_lock(&lock->osq))
458 goto fail;
459 }
460
461 for (;;) {
462 struct task_struct *owner;
463
464 /* Try to acquire the mutex... */
465 owner = __mutex_trylock_or_owner(lock);
466 if (!owner)
467 break;
468
469 /*
470 * There's an owner, wait for it to either
471 * release the lock or go to sleep.
472 */
473 if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
474 goto fail_unlock;
475
476 /*
477 * The cpu_relax() call is a compiler barrier which forces
478 * everything in this loop to be re-loaded. We don't need
479 * memory barriers as we'll eventually observe the right
480 * values at the cost of a few extra spins.
481 */
482 cpu_relax();
483 }
484
485 if (!waiter)
486 osq_unlock(&lock->osq);
487
488 return true;
489
490
491fail_unlock:
492 if (!waiter)
493 osq_unlock(&lock->osq);
494
495fail:
496 /*
497 * If we fell out of the spin path because of need_resched(),
498 * reschedule now, before we try-lock the mutex. This avoids getting
499 * scheduled out right after we obtained the mutex.
500 */
501 if (need_resched()) {
502 /*
503 * We _should_ have TASK_RUNNING here, but just in case
504 * we do not, make it so, otherwise we might get stuck.
505 */
506 __set_current_state(TASK_RUNNING);
507 schedule_preempt_disabled();
508 }
509
510 return false;
511}
512#else
513static __always_inline bool
514mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
515 struct mutex_waiter *waiter)
516{
517 return false;
518}
519#endif
520
521static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
522
523/**
524 * mutex_unlock - release the mutex
525 * @lock: the mutex to be released
526 *
527 * Unlock a mutex that has been locked by this task previously.
528 *
529 * This function must not be used in interrupt context. Unlocking
530 * of a not locked mutex is not allowed.
531 *
532 * This function is similar to (but not equivalent to) up().
533 */
534void __sched mutex_unlock(struct mutex *lock)
535{
536#ifndef CONFIG_DEBUG_LOCK_ALLOC
537 if (__mutex_unlock_fast(lock))
538 return;
539#endif
540 __mutex_unlock_slowpath(lock, _RET_IP_);
541}
542EXPORT_SYMBOL(mutex_unlock);
543
544/**
545 * ww_mutex_unlock - release the w/w mutex
546 * @lock: the mutex to be released
547 *
548 * Unlock a mutex that has been locked by this task previously with any of the
549 * ww_mutex_lock* functions (with or without an acquire context). It is
550 * forbidden to release the locks after releasing the acquire context.
551 *
552 * This function must not be used in interrupt context. Unlocking
553 * of a unlocked mutex is not allowed.
554 */
555void __sched ww_mutex_unlock(struct ww_mutex *lock)
556{
557 __ww_mutex_unlock(lock);
558 mutex_unlock(&lock->base);
559}
560EXPORT_SYMBOL(ww_mutex_unlock);
561
562/*
563 * Lock a mutex (possibly interruptible), slowpath:
564 */
565static __always_inline int __sched
566__mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclass,
567 struct lockdep_map *nest_lock, unsigned long ip,
568 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
569{
570 struct mutex_waiter waiter;
571 struct ww_mutex *ww;
572 int ret;
573
574 if (!use_ww_ctx)
575 ww_ctx = NULL;
576
577 might_sleep();
578
579 MUTEX_WARN_ON(lock->magic != lock);
580
581 ww = container_of(lock, struct ww_mutex, base);
582 if (ww_ctx) {
583 if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
584 return -EALREADY;
585
586 /*
587 * Reset the wounded flag after a kill. No other process can
588 * race and wound us here since they can't have a valid owner
589 * pointer if we don't have any locks held.
590 */
591 if (ww_ctx->acquired == 0)
592 ww_ctx->wounded = 0;
593
594#ifdef CONFIG_DEBUG_LOCK_ALLOC
595 nest_lock = &ww_ctx->dep_map;
596#endif
597 }
598
599 preempt_disable();
600 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
601
602 if (__mutex_trylock(lock) ||
603 mutex_optimistic_spin(lock, ww_ctx, NULL)) {
604 /* got the lock, yay! */
605 lock_acquired(&lock->dep_map, ip);
606 if (ww_ctx)
607 ww_mutex_set_context_fastpath(ww, ww_ctx);
608 preempt_enable();
609 return 0;
610 }
611
612 raw_spin_lock(&lock->wait_lock);
613 /*
614 * After waiting to acquire the wait_lock, try again.
615 */
616 if (__mutex_trylock(lock)) {
617 if (ww_ctx)
618 __ww_mutex_check_waiters(lock, ww_ctx);
619
620 goto skip_wait;
621 }
622
623 debug_mutex_lock_common(lock, &waiter);
624 waiter.task = current;
625 if (use_ww_ctx)
626 waiter.ww_ctx = ww_ctx;
627
628 lock_contended(&lock->dep_map, ip);
629
630 if (!use_ww_ctx) {
631 /* add waiting tasks to the end of the waitqueue (FIFO): */
632 __mutex_add_waiter(lock, &waiter, &lock->wait_list);
633 } else {
634 /*
635 * Add in stamp order, waking up waiters that must kill
636 * themselves.
637 */
638 ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
639 if (ret)
640 goto err_early_kill;
641 }
642
643 set_current_state(state);
644 for (;;) {
645 bool first;
646
647 /*
648 * Once we hold wait_lock, we're serialized against
649 * mutex_unlock() handing the lock off to us, do a trylock
650 * before testing the error conditions to make sure we pick up
651 * the handoff.
652 */
653 if (__mutex_trylock(lock))
654 goto acquired;
655
656 /*
657 * Check for signals and kill conditions while holding
658 * wait_lock. This ensures the lock cancellation is ordered
659 * against mutex_unlock() and wake-ups do not go missing.
660 */
661 if (signal_pending_state(state, current)) {
662 ret = -EINTR;
663 goto err;
664 }
665
666 if (ww_ctx) {
667 ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
668 if (ret)
669 goto err;
670 }
671
672 raw_spin_unlock(&lock->wait_lock);
673 schedule_preempt_disabled();
674
675 first = __mutex_waiter_is_first(lock, &waiter);
676
677 set_current_state(state);
678 /*
679 * Here we order against unlock; we must either see it change
680 * state back to RUNNING and fall through the next schedule(),
681 * or we must see its unlock and acquire.
682 */
683 if (__mutex_trylock_or_handoff(lock, first) ||
684 (first && mutex_optimistic_spin(lock, ww_ctx, &waiter)))
685 break;
686
687 raw_spin_lock(&lock->wait_lock);
688 }
689 raw_spin_lock(&lock->wait_lock);
690acquired:
691 __set_current_state(TASK_RUNNING);
692
693 if (ww_ctx) {
694 /*
695 * Wound-Wait; we stole the lock (!first_waiter), check the
696 * waiters as anyone might want to wound us.
697 */
698 if (!ww_ctx->is_wait_die &&
699 !__mutex_waiter_is_first(lock, &waiter))
700 __ww_mutex_check_waiters(lock, ww_ctx);
701 }
702
703 __mutex_remove_waiter(lock, &waiter);
704
705 debug_mutex_free_waiter(&waiter);
706
707skip_wait:
708 /* got the lock - cleanup and rejoice! */
709 lock_acquired(&lock->dep_map, ip);
710
711 if (ww_ctx)
712 ww_mutex_lock_acquired(ww, ww_ctx);
713
714 raw_spin_unlock(&lock->wait_lock);
715 preempt_enable();
716 return 0;
717
718err:
719 __set_current_state(TASK_RUNNING);
720 __mutex_remove_waiter(lock, &waiter);
721err_early_kill:
722 raw_spin_unlock(&lock->wait_lock);
723 debug_mutex_free_waiter(&waiter);
724 mutex_release(&lock->dep_map, ip);
725 preempt_enable();
726 return ret;
727}
728
729static int __sched
730__mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
731 struct lockdep_map *nest_lock, unsigned long ip)
732{
733 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
734}
735
736static int __sched
737__ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
738 unsigned long ip, struct ww_acquire_ctx *ww_ctx)
739{
740 return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
741}
742
743/**
744 * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
745 * @ww: mutex to lock
746 * @ww_ctx: optional w/w acquire context
747 *
748 * Trylocks a mutex with the optional acquire context; no deadlock detection is
749 * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
750 *
751 * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
752 * specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
753 *
754 * A mutex acquired with this function must be released with ww_mutex_unlock.
755 */
756int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
757{
758 if (!ww_ctx)
759 return mutex_trylock(&ww->base);
760
761 MUTEX_WARN_ON(ww->base.magic != &ww->base);
762
763 /*
764 * Reset the wounded flag after a kill. No other process can
765 * race and wound us here, since they can't have a valid owner
766 * pointer if we don't have any locks held.
767 */
768 if (ww_ctx->acquired == 0)
769 ww_ctx->wounded = 0;
770
771 if (__mutex_trylock(&ww->base)) {
772 ww_mutex_set_context_fastpath(ww, ww_ctx);
773 mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
774 return 1;
775 }
776
777 return 0;
778}
779EXPORT_SYMBOL(ww_mutex_trylock);
780
781#ifdef CONFIG_DEBUG_LOCK_ALLOC
782void __sched
783mutex_lock_nested(struct mutex *lock, unsigned int subclass)
784{
785 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
786}
787
788EXPORT_SYMBOL_GPL(mutex_lock_nested);
789
790void __sched
791_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
792{
793 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
794}
795EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
796
797int __sched
798mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
799{
800 return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
801}
802EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
803
804int __sched
805mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
806{
807 return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
808}
809EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
810
811void __sched
812mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
813{
814 int token;
815
816 might_sleep();
817
818 token = io_schedule_prepare();
819 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
820 subclass, NULL, _RET_IP_, NULL, 0);
821 io_schedule_finish(token);
822}
823EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
824
825static inline int
826ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
827{
828#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
829 unsigned tmp;
830
831 if (ctx->deadlock_inject_countdown-- == 0) {
832 tmp = ctx->deadlock_inject_interval;
833 if (tmp > UINT_MAX/4)
834 tmp = UINT_MAX;
835 else
836 tmp = tmp*2 + tmp + tmp/2;
837
838 ctx->deadlock_inject_interval = tmp;
839 ctx->deadlock_inject_countdown = tmp;
840 ctx->contending_lock = lock;
841
842 ww_mutex_unlock(lock);
843
844 return -EDEADLK;
845 }
846#endif
847
848 return 0;
849}
850
851int __sched
852ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
853{
854 int ret;
855
856 might_sleep();
857 ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
858 0, _RET_IP_, ctx);
859 if (!ret && ctx && ctx->acquired > 1)
860 return ww_mutex_deadlock_injection(lock, ctx);
861
862 return ret;
863}
864EXPORT_SYMBOL_GPL(ww_mutex_lock);
865
866int __sched
867ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
868{
869 int ret;
870
871 might_sleep();
872 ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
873 0, _RET_IP_, ctx);
874
875 if (!ret && ctx && ctx->acquired > 1)
876 return ww_mutex_deadlock_injection(lock, ctx);
877
878 return ret;
879}
880EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
881
882#endif
883
884/*
885 * Release the lock, slowpath:
886 */
887static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
888{
889 struct task_struct *next = NULL;
890 DEFINE_WAKE_Q(wake_q);
891 unsigned long owner;
892
893 mutex_release(&lock->dep_map, ip);
894
895 /*
896 * Release the lock before (potentially) taking the spinlock such that
897 * other contenders can get on with things ASAP.
898 *
899 * Except when HANDOFF, in that case we must not clear the owner field,
900 * but instead set it to the top waiter.
901 */
902 owner = atomic_long_read(&lock->owner);
903 for (;;) {
904 MUTEX_WARN_ON(__owner_task(owner) != current);
905 MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
906
907 if (owner & MUTEX_FLAG_HANDOFF)
908 break;
909
910 if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
911 if (owner & MUTEX_FLAG_WAITERS)
912 break;
913
914 return;
915 }
916 }
917
918 raw_spin_lock(&lock->wait_lock);
919 debug_mutex_unlock(lock);
920 if (!list_empty(&lock->wait_list)) {
921 /* get the first entry from the wait-list: */
922 struct mutex_waiter *waiter =
923 list_first_entry(&lock->wait_list,
924 struct mutex_waiter, list);
925
926 next = waiter->task;
927
928 debug_mutex_wake_waiter(lock, waiter);
929 wake_q_add(&wake_q, next);
930 }
931
932 if (owner & MUTEX_FLAG_HANDOFF)
933 __mutex_handoff(lock, next);
934
935 raw_spin_unlock(&lock->wait_lock);
936
937 wake_up_q(&wake_q);
938}
939
940#ifndef CONFIG_DEBUG_LOCK_ALLOC
941/*
942 * Here come the less common (and hence less performance-critical) APIs:
943 * mutex_lock_interruptible() and mutex_trylock().
944 */
945static noinline int __sched
946__mutex_lock_killable_slowpath(struct mutex *lock);
947
948static noinline int __sched
949__mutex_lock_interruptible_slowpath(struct mutex *lock);
950
951/**
952 * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
953 * @lock: The mutex to be acquired.
954 *
955 * Lock the mutex like mutex_lock(). If a signal is delivered while the
956 * process is sleeping, this function will return without acquiring the
957 * mutex.
958 *
959 * Context: Process context.
960 * Return: 0 if the lock was successfully acquired or %-EINTR if a
961 * signal arrived.
962 */
963int __sched mutex_lock_interruptible(struct mutex *lock)
964{
965 might_sleep();
966
967 if (__mutex_trylock_fast(lock))
968 return 0;
969
970 return __mutex_lock_interruptible_slowpath(lock);
971}
972
973EXPORT_SYMBOL(mutex_lock_interruptible);
974
975/**
976 * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
977 * @lock: The mutex to be acquired.
978 *
979 * Lock the mutex like mutex_lock(). If a signal which will be fatal to
980 * the current process is delivered while the process is sleeping, this
981 * function will return without acquiring the mutex.
982 *
983 * Context: Process context.
984 * Return: 0 if the lock was successfully acquired or %-EINTR if a
985 * fatal signal arrived.
986 */
987int __sched mutex_lock_killable(struct mutex *lock)
988{
989 might_sleep();
990
991 if (__mutex_trylock_fast(lock))
992 return 0;
993
994 return __mutex_lock_killable_slowpath(lock);
995}
996EXPORT_SYMBOL(mutex_lock_killable);
997
998/**
999 * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1000 * @lock: The mutex to be acquired.
1001 *
1002 * Lock the mutex like mutex_lock(). While the task is waiting for this
1003 * mutex, it will be accounted as being in the IO wait state by the
1004 * scheduler.
1005 *
1006 * Context: Process context.
1007 */
1008void __sched mutex_lock_io(struct mutex *lock)
1009{
1010 int token;
1011
1012 token = io_schedule_prepare();
1013 mutex_lock(lock);
1014 io_schedule_finish(token);
1015}
1016EXPORT_SYMBOL_GPL(mutex_lock_io);
1017
1018static noinline void __sched
1019__mutex_lock_slowpath(struct mutex *lock)
1020{
1021 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1022}
1023
1024static noinline int __sched
1025__mutex_lock_killable_slowpath(struct mutex *lock)
1026{
1027 return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1028}
1029
1030static noinline int __sched
1031__mutex_lock_interruptible_slowpath(struct mutex *lock)
1032{
1033 return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1034}
1035
1036static noinline int __sched
1037__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1038{
1039 return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0,
1040 _RET_IP_, ctx);
1041}
1042
1043static noinline int __sched
1044__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1045 struct ww_acquire_ctx *ctx)
1046{
1047 return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0,
1048 _RET_IP_, ctx);
1049}
1050
1051#endif
1052
1053/**
1054 * mutex_trylock - try to acquire the mutex, without waiting
1055 * @lock: the mutex to be acquired
1056 *
1057 * Try to acquire the mutex atomically. Returns 1 if the mutex
1058 * has been acquired successfully, and 0 on contention.
1059 *
1060 * NOTE: this function follows the spin_trylock() convention, so
1061 * it is negated from the down_trylock() return values! Be careful
1062 * about this when converting semaphore users to mutexes.
1063 *
1064 * This function must not be used in interrupt context. The
1065 * mutex must be released by the same task that acquired it.
1066 */
1067int __sched mutex_trylock(struct mutex *lock)
1068{
1069 bool locked;
1070
1071 MUTEX_WARN_ON(lock->magic != lock);
1072
1073 locked = __mutex_trylock(lock);
1074 if (locked)
1075 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1076
1077 return locked;
1078}
1079EXPORT_SYMBOL(mutex_trylock);
1080
1081#ifndef CONFIG_DEBUG_LOCK_ALLOC
1082int __sched
1083ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1084{
1085 might_sleep();
1086
1087 if (__mutex_trylock_fast(&lock->base)) {
1088 if (ctx)
1089 ww_mutex_set_context_fastpath(lock, ctx);
1090 return 0;
1091 }
1092
1093 return __ww_mutex_lock_slowpath(lock, ctx);
1094}
1095EXPORT_SYMBOL(ww_mutex_lock);
1096
1097int __sched
1098ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1099{
1100 might_sleep();
1101
1102 if (__mutex_trylock_fast(&lock->base)) {
1103 if (ctx)
1104 ww_mutex_set_context_fastpath(lock, ctx);
1105 return 0;
1106 }
1107
1108 return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1109}
1110EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1111
1112#endif /* !CONFIG_DEBUG_LOCK_ALLOC */
1113#endif /* !CONFIG_PREEMPT_RT */
1114
1115/**
1116 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1117 * @cnt: the atomic which we are to dec
1118 * @lock: the mutex to return holding if we dec to 0
1119 *
1120 * return true and hold lock if we dec to 0, return false otherwise
1121 */
1122int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1123{
1124 /* dec if we can't possibly hit 0 */
1125 if (atomic_add_unless(cnt, -1, 1))
1126 return 0;
1127 /* we might hit 0, so take the lock */
1128 mutex_lock(lock);
1129 if (!atomic_dec_and_test(cnt)) {
1130 /* when we actually did the dec, we didn't hit 0 */
1131 mutex_unlock(lock);
1132 return 0;
1133 }
1134 /* we hit 0, and we hold the lock */
1135 return 1;
1136}
1137EXPORT_SYMBOL(atomic_dec_and_mutex_lock);