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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/locking/mutex-design.txt.
19 */
20#include <linux/mutex.h>
21#include <linux/ww_mutex.h>
22#include <linux/sched/signal.h>
23#include <linux/sched/rt.h>
24#include <linux/sched/wake_q.h>
25#include <linux/sched/debug.h>
26#include <linux/export.h>
27#include <linux/spinlock.h>
28#include <linux/interrupt.h>
29#include <linux/debug_locks.h>
30#include <linux/osq_lock.h>
31
32#ifdef CONFIG_DEBUG_MUTEXES
33# include "mutex-debug.h"
34#else
35# include "mutex.h"
36#endif
37
38void
39__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
40{
41 atomic_long_set(&lock->owner, 0);
42 spin_lock_init(&lock->wait_lock);
43 INIT_LIST_HEAD(&lock->wait_list);
44#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
45 osq_lock_init(&lock->osq);
46#endif
47
48 debug_mutex_init(lock, name, key);
49}
50EXPORT_SYMBOL(__mutex_init);
51
52/*
53 * @owner: contains: 'struct task_struct *' to the current lock owner,
54 * NULL means not owned. Since task_struct pointers are aligned at
55 * at least L1_CACHE_BYTES, we have low bits to store extra state.
56 *
57 * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
58 * Bit1 indicates unlock needs to hand the lock to the top-waiter
59 * Bit2 indicates handoff has been done and we're waiting for pickup.
60 */
61#define MUTEX_FLAG_WAITERS 0x01
62#define MUTEX_FLAG_HANDOFF 0x02
63#define MUTEX_FLAG_PICKUP 0x04
64
65#define MUTEX_FLAGS 0x07
66
67static inline struct task_struct *__owner_task(unsigned long owner)
68{
69 return (struct task_struct *)(owner & ~MUTEX_FLAGS);
70}
71
72static inline unsigned long __owner_flags(unsigned long owner)
73{
74 return owner & MUTEX_FLAGS;
75}
76
77/*
78 * Trylock variant that retuns the owning task on failure.
79 */
80static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
81{
82 unsigned long owner, curr = (unsigned long)current;
83
84 owner = atomic_long_read(&lock->owner);
85 for (;;) { /* must loop, can race against a flag */
86 unsigned long old, flags = __owner_flags(owner);
87 unsigned long task = owner & ~MUTEX_FLAGS;
88
89 if (task) {
90 if (likely(task != curr))
91 break;
92
93 if (likely(!(flags & MUTEX_FLAG_PICKUP)))
94 break;
95
96 flags &= ~MUTEX_FLAG_PICKUP;
97 } else {
98#ifdef CONFIG_DEBUG_MUTEXES
99 DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
100#endif
101 }
102
103 /*
104 * We set the HANDOFF bit, we must make sure it doesn't live
105 * past the point where we acquire it. This would be possible
106 * if we (accidentally) set the bit on an unlocked mutex.
107 */
108 flags &= ~MUTEX_FLAG_HANDOFF;
109
110 old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
111 if (old == owner)
112 return NULL;
113
114 owner = old;
115 }
116
117 return __owner_task(owner);
118}
119
120/*
121 * Actual trylock that will work on any unlocked state.
122 */
123static inline bool __mutex_trylock(struct mutex *lock)
124{
125 return !__mutex_trylock_or_owner(lock);
126}
127
128#ifndef CONFIG_DEBUG_LOCK_ALLOC
129/*
130 * Lockdep annotations are contained to the slow paths for simplicity.
131 * There is nothing that would stop spreading the lockdep annotations outwards
132 * except more code.
133 */
134
135/*
136 * Optimistic trylock that only works in the uncontended case. Make sure to
137 * follow with a __mutex_trylock() before failing.
138 */
139static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
140{
141 unsigned long curr = (unsigned long)current;
142
143 if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr))
144 return true;
145
146 return false;
147}
148
149static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
150{
151 unsigned long curr = (unsigned long)current;
152
153 if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
154 return true;
155
156 return false;
157}
158#endif
159
160static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
161{
162 atomic_long_or(flag, &lock->owner);
163}
164
165static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
166{
167 atomic_long_andnot(flag, &lock->owner);
168}
169
170static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
171{
172 return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
173}
174
175/*
176 * Give up ownership to a specific task, when @task = NULL, this is equivalent
177 * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
178 * WAITERS. Provides RELEASE semantics like a regular unlock, the
179 * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
180 */
181static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
182{
183 unsigned long owner = atomic_long_read(&lock->owner);
184
185 for (;;) {
186 unsigned long old, new;
187
188#ifdef CONFIG_DEBUG_MUTEXES
189 DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
190 DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
191#endif
192
193 new = (owner & MUTEX_FLAG_WAITERS);
194 new |= (unsigned long)task;
195 if (task)
196 new |= MUTEX_FLAG_PICKUP;
197
198 old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
199 if (old == owner)
200 break;
201
202 owner = old;
203 }
204}
205
206#ifndef CONFIG_DEBUG_LOCK_ALLOC
207/*
208 * We split the mutex lock/unlock logic into separate fastpath and
209 * slowpath functions, to reduce the register pressure on the fastpath.
210 * We also put the fastpath first in the kernel image, to make sure the
211 * branch is predicted by the CPU as default-untaken.
212 */
213static void __sched __mutex_lock_slowpath(struct mutex *lock);
214
215/**
216 * mutex_lock - acquire the mutex
217 * @lock: the mutex to be acquired
218 *
219 * Lock the mutex exclusively for this task. If the mutex is not
220 * available right now, it will sleep until it can get it.
221 *
222 * The mutex must later on be released by the same task that
223 * acquired it. Recursive locking is not allowed. The task
224 * may not exit without first unlocking the mutex. Also, kernel
225 * memory where the mutex resides must not be freed with
226 * the mutex still locked. The mutex must first be initialized
227 * (or statically defined) before it can be locked. memset()-ing
228 * the mutex to 0 is not allowed.
229 *
230 * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
231 * checks that will enforce the restrictions and will also do
232 * deadlock debugging)
233 *
234 * This function is similar to (but not equivalent to) down().
235 */
236void __sched mutex_lock(struct mutex *lock)
237{
238 might_sleep();
239
240 if (!__mutex_trylock_fast(lock))
241 __mutex_lock_slowpath(lock);
242}
243EXPORT_SYMBOL(mutex_lock);
244#endif
245
246static __always_inline void
247ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
248{
249#ifdef CONFIG_DEBUG_MUTEXES
250 /*
251 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
252 * but released with a normal mutex_unlock in this call.
253 *
254 * This should never happen, always use ww_mutex_unlock.
255 */
256 DEBUG_LOCKS_WARN_ON(ww->ctx);
257
258 /*
259 * Not quite done after calling ww_acquire_done() ?
260 */
261 DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
262
263 if (ww_ctx->contending_lock) {
264 /*
265 * After -EDEADLK you tried to
266 * acquire a different ww_mutex? Bad!
267 */
268 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
269
270 /*
271 * You called ww_mutex_lock after receiving -EDEADLK,
272 * but 'forgot' to unlock everything else first?
273 */
274 DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
275 ww_ctx->contending_lock = NULL;
276 }
277
278 /*
279 * Naughty, using a different class will lead to undefined behavior!
280 */
281 DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
282#endif
283 ww_ctx->acquired++;
284}
285
286static inline bool __sched
287__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
288{
289 return a->stamp - b->stamp <= LONG_MAX &&
290 (a->stamp != b->stamp || a > b);
291}
292
293/*
294 * Wake up any waiters that may have to back off when the lock is held by the
295 * given context.
296 *
297 * Due to the invariants on the wait list, this can only affect the first
298 * waiter with a context.
299 *
300 * The current task must not be on the wait list.
301 */
302static void __sched
303__ww_mutex_wakeup_for_backoff(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
304{
305 struct mutex_waiter *cur;
306
307 lockdep_assert_held(&lock->wait_lock);
308
309 list_for_each_entry(cur, &lock->wait_list, list) {
310 if (!cur->ww_ctx)
311 continue;
312
313 if (cur->ww_ctx->acquired > 0 &&
314 __ww_ctx_stamp_after(cur->ww_ctx, ww_ctx)) {
315 debug_mutex_wake_waiter(lock, cur);
316 wake_up_process(cur->task);
317 }
318
319 break;
320 }
321}
322
323/*
324 * After acquiring lock with fastpath or when we lost out in contested
325 * slowpath, set ctx and wake up any waiters so they can recheck.
326 */
327static __always_inline void
328ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
329{
330 ww_mutex_lock_acquired(lock, ctx);
331
332 lock->ctx = ctx;
333
334 /*
335 * The lock->ctx update should be visible on all cores before
336 * the atomic read is done, otherwise contended waiters might be
337 * missed. The contended waiters will either see ww_ctx == NULL
338 * and keep spinning, or it will acquire wait_lock, add itself
339 * to waiter list and sleep.
340 */
341 smp_mb(); /* ^^^ */
342
343 /*
344 * Check if lock is contended, if not there is nobody to wake up
345 */
346 if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
347 return;
348
349 /*
350 * Uh oh, we raced in fastpath, wake up everyone in this case,
351 * so they can see the new lock->ctx.
352 */
353 spin_lock(&lock->base.wait_lock);
354 __ww_mutex_wakeup_for_backoff(&lock->base, ctx);
355 spin_unlock(&lock->base.wait_lock);
356}
357
358/*
359 * After acquiring lock in the slowpath set ctx.
360 *
361 * Unlike for the fast path, the caller ensures that waiters are woken up where
362 * necessary.
363 *
364 * Callers must hold the mutex wait_lock.
365 */
366static __always_inline void
367ww_mutex_set_context_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
368{
369 ww_mutex_lock_acquired(lock, ctx);
370 lock->ctx = ctx;
371}
372
373#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
374
375static inline
376bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
377 struct mutex_waiter *waiter)
378{
379 struct ww_mutex *ww;
380
381 ww = container_of(lock, struct ww_mutex, base);
382
383 /*
384 * If ww->ctx is set the contents are undefined, only
385 * by acquiring wait_lock there is a guarantee that
386 * they are not invalid when reading.
387 *
388 * As such, when deadlock detection needs to be
389 * performed the optimistic spinning cannot be done.
390 *
391 * Check this in every inner iteration because we may
392 * be racing against another thread's ww_mutex_lock.
393 */
394 if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
395 return false;
396
397 /*
398 * If we aren't on the wait list yet, cancel the spin
399 * if there are waiters. We want to avoid stealing the
400 * lock from a waiter with an earlier stamp, since the
401 * other thread may already own a lock that we also
402 * need.
403 */
404 if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
405 return false;
406
407 /*
408 * Similarly, stop spinning if we are no longer the
409 * first waiter.
410 */
411 if (waiter && !__mutex_waiter_is_first(lock, waiter))
412 return false;
413
414 return true;
415}
416
417/*
418 * Look out! "owner" is an entirely speculative pointer access and not
419 * reliable.
420 *
421 * "noinline" so that this function shows up on perf profiles.
422 */
423static noinline
424bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
425 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
426{
427 bool ret = true;
428
429 rcu_read_lock();
430 while (__mutex_owner(lock) == owner) {
431 /*
432 * Ensure we emit the owner->on_cpu, dereference _after_
433 * checking lock->owner still matches owner. If that fails,
434 * owner might point to freed memory. If it still matches,
435 * the rcu_read_lock() ensures the memory stays valid.
436 */
437 barrier();
438
439 /*
440 * Use vcpu_is_preempted to detect lock holder preemption issue.
441 */
442 if (!owner->on_cpu || need_resched() ||
443 vcpu_is_preempted(task_cpu(owner))) {
444 ret = false;
445 break;
446 }
447
448 if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
449 ret = false;
450 break;
451 }
452
453 cpu_relax();
454 }
455 rcu_read_unlock();
456
457 return ret;
458}
459
460/*
461 * Initial check for entering the mutex spinning loop
462 */
463static inline int mutex_can_spin_on_owner(struct mutex *lock)
464{
465 struct task_struct *owner;
466 int retval = 1;
467
468 if (need_resched())
469 return 0;
470
471 rcu_read_lock();
472 owner = __mutex_owner(lock);
473
474 /*
475 * As lock holder preemption issue, we both skip spinning if task is not
476 * on cpu or its cpu is preempted
477 */
478 if (owner)
479 retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
480 rcu_read_unlock();
481
482 /*
483 * If lock->owner is not set, the mutex has been released. Return true
484 * such that we'll trylock in the spin path, which is a faster option
485 * than the blocking slow path.
486 */
487 return retval;
488}
489
490/*
491 * Optimistic spinning.
492 *
493 * We try to spin for acquisition when we find that the lock owner
494 * is currently running on a (different) CPU and while we don't
495 * need to reschedule. The rationale is that if the lock owner is
496 * running, it is likely to release the lock soon.
497 *
498 * The mutex spinners are queued up using MCS lock so that only one
499 * spinner can compete for the mutex. However, if mutex spinning isn't
500 * going to happen, there is no point in going through the lock/unlock
501 * overhead.
502 *
503 * Returns true when the lock was taken, otherwise false, indicating
504 * that we need to jump to the slowpath and sleep.
505 *
506 * The waiter flag is set to true if the spinner is a waiter in the wait
507 * queue. The waiter-spinner will spin on the lock directly and concurrently
508 * with the spinner at the head of the OSQ, if present, until the owner is
509 * changed to itself.
510 */
511static __always_inline bool
512mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
513 const bool use_ww_ctx, struct mutex_waiter *waiter)
514{
515 if (!waiter) {
516 /*
517 * The purpose of the mutex_can_spin_on_owner() function is
518 * to eliminate the overhead of osq_lock() and osq_unlock()
519 * in case spinning isn't possible. As a waiter-spinner
520 * is not going to take OSQ lock anyway, there is no need
521 * to call mutex_can_spin_on_owner().
522 */
523 if (!mutex_can_spin_on_owner(lock))
524 goto fail;
525
526 /*
527 * In order to avoid a stampede of mutex spinners trying to
528 * acquire the mutex all at once, the spinners need to take a
529 * MCS (queued) lock first before spinning on the owner field.
530 */
531 if (!osq_lock(&lock->osq))
532 goto fail;
533 }
534
535 for (;;) {
536 struct task_struct *owner;
537
538 /* Try to acquire the mutex... */
539 owner = __mutex_trylock_or_owner(lock);
540 if (!owner)
541 break;
542
543 /*
544 * There's an owner, wait for it to either
545 * release the lock or go to sleep.
546 */
547 if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
548 goto fail_unlock;
549
550 /*
551 * The cpu_relax() call is a compiler barrier which forces
552 * everything in this loop to be re-loaded. We don't need
553 * memory barriers as we'll eventually observe the right
554 * values at the cost of a few extra spins.
555 */
556 cpu_relax();
557 }
558
559 if (!waiter)
560 osq_unlock(&lock->osq);
561
562 return true;
563
564
565fail_unlock:
566 if (!waiter)
567 osq_unlock(&lock->osq);
568
569fail:
570 /*
571 * If we fell out of the spin path because of need_resched(),
572 * reschedule now, before we try-lock the mutex. This avoids getting
573 * scheduled out right after we obtained the mutex.
574 */
575 if (need_resched()) {
576 /*
577 * We _should_ have TASK_RUNNING here, but just in case
578 * we do not, make it so, otherwise we might get stuck.
579 */
580 __set_current_state(TASK_RUNNING);
581 schedule_preempt_disabled();
582 }
583
584 return false;
585}
586#else
587static __always_inline bool
588mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
589 const bool use_ww_ctx, struct mutex_waiter *waiter)
590{
591 return false;
592}
593#endif
594
595static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
596
597/**
598 * mutex_unlock - release the mutex
599 * @lock: the mutex to be released
600 *
601 * Unlock a mutex that has been locked by this task previously.
602 *
603 * This function must not be used in interrupt context. Unlocking
604 * of a not locked mutex is not allowed.
605 *
606 * This function is similar to (but not equivalent to) up().
607 */
608void __sched mutex_unlock(struct mutex *lock)
609{
610#ifndef CONFIG_DEBUG_LOCK_ALLOC
611 if (__mutex_unlock_fast(lock))
612 return;
613#endif
614 __mutex_unlock_slowpath(lock, _RET_IP_);
615}
616EXPORT_SYMBOL(mutex_unlock);
617
618/**
619 * ww_mutex_unlock - release the w/w mutex
620 * @lock: the mutex to be released
621 *
622 * Unlock a mutex that has been locked by this task previously with any of the
623 * ww_mutex_lock* functions (with or without an acquire context). It is
624 * forbidden to release the locks after releasing the acquire context.
625 *
626 * This function must not be used in interrupt context. Unlocking
627 * of a unlocked mutex is not allowed.
628 */
629void __sched ww_mutex_unlock(struct ww_mutex *lock)
630{
631 /*
632 * The unlocking fastpath is the 0->1 transition from 'locked'
633 * into 'unlocked' state:
634 */
635 if (lock->ctx) {
636#ifdef CONFIG_DEBUG_MUTEXES
637 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
638#endif
639 if (lock->ctx->acquired > 0)
640 lock->ctx->acquired--;
641 lock->ctx = NULL;
642 }
643
644 mutex_unlock(&lock->base);
645}
646EXPORT_SYMBOL(ww_mutex_unlock);
647
648static inline int __sched
649__ww_mutex_lock_check_stamp(struct mutex *lock, struct mutex_waiter *waiter,
650 struct ww_acquire_ctx *ctx)
651{
652 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
653 struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
654 struct mutex_waiter *cur;
655
656 if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
657 goto deadlock;
658
659 /*
660 * If there is a waiter in front of us that has a context, then its
661 * stamp is earlier than ours and we must back off.
662 */
663 cur = waiter;
664 list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
665 if (cur->ww_ctx)
666 goto deadlock;
667 }
668
669 return 0;
670
671deadlock:
672#ifdef CONFIG_DEBUG_MUTEXES
673 DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
674 ctx->contending_lock = ww;
675#endif
676 return -EDEADLK;
677}
678
679static inline int __sched
680__ww_mutex_add_waiter(struct mutex_waiter *waiter,
681 struct mutex *lock,
682 struct ww_acquire_ctx *ww_ctx)
683{
684 struct mutex_waiter *cur;
685 struct list_head *pos;
686
687 if (!ww_ctx) {
688 list_add_tail(&waiter->list, &lock->wait_list);
689 return 0;
690 }
691
692 /*
693 * Add the waiter before the first waiter with a higher stamp.
694 * Waiters without a context are skipped to avoid starving
695 * them.
696 */
697 pos = &lock->wait_list;
698 list_for_each_entry_reverse(cur, &lock->wait_list, list) {
699 if (!cur->ww_ctx)
700 continue;
701
702 if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
703 /* Back off immediately if necessary. */
704 if (ww_ctx->acquired > 0) {
705#ifdef CONFIG_DEBUG_MUTEXES
706 struct ww_mutex *ww;
707
708 ww = container_of(lock, struct ww_mutex, base);
709 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
710 ww_ctx->contending_lock = ww;
711#endif
712 return -EDEADLK;
713 }
714
715 break;
716 }
717
718 pos = &cur->list;
719
720 /*
721 * Wake up the waiter so that it gets a chance to back
722 * off.
723 */
724 if (cur->ww_ctx->acquired > 0) {
725 debug_mutex_wake_waiter(lock, cur);
726 wake_up_process(cur->task);
727 }
728 }
729
730 list_add_tail(&waiter->list, pos);
731 return 0;
732}
733
734/*
735 * Lock a mutex (possibly interruptible), slowpath:
736 */
737static __always_inline int __sched
738__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
739 struct lockdep_map *nest_lock, unsigned long ip,
740 struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
741{
742 struct mutex_waiter waiter;
743 bool first = false;
744 struct ww_mutex *ww;
745 int ret;
746
747 might_sleep();
748
749 ww = container_of(lock, struct ww_mutex, base);
750 if (use_ww_ctx && ww_ctx) {
751 if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
752 return -EALREADY;
753 }
754
755 preempt_disable();
756 mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
757
758 if (__mutex_trylock(lock) ||
759 mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
760 /* got the lock, yay! */
761 lock_acquired(&lock->dep_map, ip);
762 if (use_ww_ctx && ww_ctx)
763 ww_mutex_set_context_fastpath(ww, ww_ctx);
764 preempt_enable();
765 return 0;
766 }
767
768 spin_lock(&lock->wait_lock);
769 /*
770 * After waiting to acquire the wait_lock, try again.
771 */
772 if (__mutex_trylock(lock)) {
773 if (use_ww_ctx && ww_ctx)
774 __ww_mutex_wakeup_for_backoff(lock, ww_ctx);
775
776 goto skip_wait;
777 }
778
779 debug_mutex_lock_common(lock, &waiter);
780 debug_mutex_add_waiter(lock, &waiter, current);
781
782 lock_contended(&lock->dep_map, ip);
783
784 if (!use_ww_ctx) {
785 /* add waiting tasks to the end of the waitqueue (FIFO): */
786 list_add_tail(&waiter.list, &lock->wait_list);
787
788#ifdef CONFIG_DEBUG_MUTEXES
789 waiter.ww_ctx = MUTEX_POISON_WW_CTX;
790#endif
791 } else {
792 /* Add in stamp order, waking up waiters that must back off. */
793 ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
794 if (ret)
795 goto err_early_backoff;
796
797 waiter.ww_ctx = ww_ctx;
798 }
799
800 waiter.task = current;
801
802 if (__mutex_waiter_is_first(lock, &waiter))
803 __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
804
805 set_current_state(state);
806 for (;;) {
807 /*
808 * Once we hold wait_lock, we're serialized against
809 * mutex_unlock() handing the lock off to us, do a trylock
810 * before testing the error conditions to make sure we pick up
811 * the handoff.
812 */
813 if (__mutex_trylock(lock))
814 goto acquired;
815
816 /*
817 * Check for signals and wound conditions while holding
818 * wait_lock. This ensures the lock cancellation is ordered
819 * against mutex_unlock() and wake-ups do not go missing.
820 */
821 if (unlikely(signal_pending_state(state, current))) {
822 ret = -EINTR;
823 goto err;
824 }
825
826 if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
827 ret = __ww_mutex_lock_check_stamp(lock, &waiter, ww_ctx);
828 if (ret)
829 goto err;
830 }
831
832 spin_unlock(&lock->wait_lock);
833 schedule_preempt_disabled();
834
835 /*
836 * ww_mutex needs to always recheck its position since its waiter
837 * list is not FIFO ordered.
838 */
839 if ((use_ww_ctx && ww_ctx) || !first) {
840 first = __mutex_waiter_is_first(lock, &waiter);
841 if (first)
842 __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
843 }
844
845 set_current_state(state);
846 /*
847 * Here we order against unlock; we must either see it change
848 * state back to RUNNING and fall through the next schedule(),
849 * or we must see its unlock and acquire.
850 */
851 if (__mutex_trylock(lock) ||
852 (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
853 break;
854
855 spin_lock(&lock->wait_lock);
856 }
857 spin_lock(&lock->wait_lock);
858acquired:
859 __set_current_state(TASK_RUNNING);
860
861 mutex_remove_waiter(lock, &waiter, current);
862 if (likely(list_empty(&lock->wait_list)))
863 __mutex_clear_flag(lock, MUTEX_FLAGS);
864
865 debug_mutex_free_waiter(&waiter);
866
867skip_wait:
868 /* got the lock - cleanup and rejoice! */
869 lock_acquired(&lock->dep_map, ip);
870
871 if (use_ww_ctx && ww_ctx)
872 ww_mutex_set_context_slowpath(ww, ww_ctx);
873
874 spin_unlock(&lock->wait_lock);
875 preempt_enable();
876 return 0;
877
878err:
879 __set_current_state(TASK_RUNNING);
880 mutex_remove_waiter(lock, &waiter, current);
881err_early_backoff:
882 spin_unlock(&lock->wait_lock);
883 debug_mutex_free_waiter(&waiter);
884 mutex_release(&lock->dep_map, 1, ip);
885 preempt_enable();
886 return ret;
887}
888
889static int __sched
890__mutex_lock(struct mutex *lock, long state, unsigned int subclass,
891 struct lockdep_map *nest_lock, unsigned long ip)
892{
893 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
894}
895
896static int __sched
897__ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
898 struct lockdep_map *nest_lock, unsigned long ip,
899 struct ww_acquire_ctx *ww_ctx)
900{
901 return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
902}
903
904#ifdef CONFIG_DEBUG_LOCK_ALLOC
905void __sched
906mutex_lock_nested(struct mutex *lock, unsigned int subclass)
907{
908 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
909}
910
911EXPORT_SYMBOL_GPL(mutex_lock_nested);
912
913void __sched
914_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
915{
916 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
917}
918EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
919
920int __sched
921mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
922{
923 return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
924}
925EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
926
927int __sched
928mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
929{
930 return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
931}
932EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
933
934void __sched
935mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
936{
937 int token;
938
939 might_sleep();
940
941 token = io_schedule_prepare();
942 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
943 subclass, NULL, _RET_IP_, NULL, 0);
944 io_schedule_finish(token);
945}
946EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
947
948static inline int
949ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
950{
951#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
952 unsigned tmp;
953
954 if (ctx->deadlock_inject_countdown-- == 0) {
955 tmp = ctx->deadlock_inject_interval;
956 if (tmp > UINT_MAX/4)
957 tmp = UINT_MAX;
958 else
959 tmp = tmp*2 + tmp + tmp/2;
960
961 ctx->deadlock_inject_interval = tmp;
962 ctx->deadlock_inject_countdown = tmp;
963 ctx->contending_lock = lock;
964
965 ww_mutex_unlock(lock);
966
967 return -EDEADLK;
968 }
969#endif
970
971 return 0;
972}
973
974int __sched
975ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
976{
977 int ret;
978
979 might_sleep();
980 ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
981 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
982 ctx);
983 if (!ret && ctx && ctx->acquired > 1)
984 return ww_mutex_deadlock_injection(lock, ctx);
985
986 return ret;
987}
988EXPORT_SYMBOL_GPL(ww_mutex_lock);
989
990int __sched
991ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
992{
993 int ret;
994
995 might_sleep();
996 ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
997 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
998 ctx);
999
1000 if (!ret && ctx && ctx->acquired > 1)
1001 return ww_mutex_deadlock_injection(lock, ctx);
1002
1003 return ret;
1004}
1005EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
1006
1007#endif
1008
1009/*
1010 * Release the lock, slowpath:
1011 */
1012static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
1013{
1014 struct task_struct *next = NULL;
1015 DEFINE_WAKE_Q(wake_q);
1016 unsigned long owner;
1017
1018 mutex_release(&lock->dep_map, 1, ip);
1019
1020 /*
1021 * Release the lock before (potentially) taking the spinlock such that
1022 * other contenders can get on with things ASAP.
1023 *
1024 * Except when HANDOFF, in that case we must not clear the owner field,
1025 * but instead set it to the top waiter.
1026 */
1027 owner = atomic_long_read(&lock->owner);
1028 for (;;) {
1029 unsigned long old;
1030
1031#ifdef CONFIG_DEBUG_MUTEXES
1032 DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
1033 DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
1034#endif
1035
1036 if (owner & MUTEX_FLAG_HANDOFF)
1037 break;
1038
1039 old = atomic_long_cmpxchg_release(&lock->owner, owner,
1040 __owner_flags(owner));
1041 if (old == owner) {
1042 if (owner & MUTEX_FLAG_WAITERS)
1043 break;
1044
1045 return;
1046 }
1047
1048 owner = old;
1049 }
1050
1051 spin_lock(&lock->wait_lock);
1052 debug_mutex_unlock(lock);
1053 if (!list_empty(&lock->wait_list)) {
1054 /* get the first entry from the wait-list: */
1055 struct mutex_waiter *waiter =
1056 list_first_entry(&lock->wait_list,
1057 struct mutex_waiter, list);
1058
1059 next = waiter->task;
1060
1061 debug_mutex_wake_waiter(lock, waiter);
1062 wake_q_add(&wake_q, next);
1063 }
1064
1065 if (owner & MUTEX_FLAG_HANDOFF)
1066 __mutex_handoff(lock, next);
1067
1068 spin_unlock(&lock->wait_lock);
1069
1070 wake_up_q(&wake_q);
1071}
1072
1073#ifndef CONFIG_DEBUG_LOCK_ALLOC
1074/*
1075 * Here come the less common (and hence less performance-critical) APIs:
1076 * mutex_lock_interruptible() and mutex_trylock().
1077 */
1078static noinline int __sched
1079__mutex_lock_killable_slowpath(struct mutex *lock);
1080
1081static noinline int __sched
1082__mutex_lock_interruptible_slowpath(struct mutex *lock);
1083
1084/**
1085 * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
1086 * @lock: The mutex to be acquired.
1087 *
1088 * Lock the mutex like mutex_lock(). If a signal is delivered while the
1089 * process is sleeping, this function will return without acquiring the
1090 * mutex.
1091 *
1092 * Context: Process context.
1093 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1094 * signal arrived.
1095 */
1096int __sched mutex_lock_interruptible(struct mutex *lock)
1097{
1098 might_sleep();
1099
1100 if (__mutex_trylock_fast(lock))
1101 return 0;
1102
1103 return __mutex_lock_interruptible_slowpath(lock);
1104}
1105
1106EXPORT_SYMBOL(mutex_lock_interruptible);
1107
1108/**
1109 * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
1110 * @lock: The mutex to be acquired.
1111 *
1112 * Lock the mutex like mutex_lock(). If a signal which will be fatal to
1113 * the current process is delivered while the process is sleeping, this
1114 * function will return without acquiring the mutex.
1115 *
1116 * Context: Process context.
1117 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1118 * fatal signal arrived.
1119 */
1120int __sched mutex_lock_killable(struct mutex *lock)
1121{
1122 might_sleep();
1123
1124 if (__mutex_trylock_fast(lock))
1125 return 0;
1126
1127 return __mutex_lock_killable_slowpath(lock);
1128}
1129EXPORT_SYMBOL(mutex_lock_killable);
1130
1131/**
1132 * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1133 * @lock: The mutex to be acquired.
1134 *
1135 * Lock the mutex like mutex_lock(). While the task is waiting for this
1136 * mutex, it will be accounted as being in the IO wait state by the
1137 * scheduler.
1138 *
1139 * Context: Process context.
1140 */
1141void __sched mutex_lock_io(struct mutex *lock)
1142{
1143 int token;
1144
1145 token = io_schedule_prepare();
1146 mutex_lock(lock);
1147 io_schedule_finish(token);
1148}
1149EXPORT_SYMBOL_GPL(mutex_lock_io);
1150
1151static noinline void __sched
1152__mutex_lock_slowpath(struct mutex *lock)
1153{
1154 __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1155}
1156
1157static noinline int __sched
1158__mutex_lock_killable_slowpath(struct mutex *lock)
1159{
1160 return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1161}
1162
1163static noinline int __sched
1164__mutex_lock_interruptible_slowpath(struct mutex *lock)
1165{
1166 return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1167}
1168
1169static noinline int __sched
1170__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1171{
1172 return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
1173 _RET_IP_, ctx);
1174}
1175
1176static noinline int __sched
1177__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1178 struct ww_acquire_ctx *ctx)
1179{
1180 return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
1181 _RET_IP_, ctx);
1182}
1183
1184#endif
1185
1186/**
1187 * mutex_trylock - try to acquire the mutex, without waiting
1188 * @lock: the mutex to be acquired
1189 *
1190 * Try to acquire the mutex atomically. Returns 1 if the mutex
1191 * has been acquired successfully, and 0 on contention.
1192 *
1193 * NOTE: this function follows the spin_trylock() convention, so
1194 * it is negated from the down_trylock() return values! Be careful
1195 * about this when converting semaphore users to mutexes.
1196 *
1197 * This function must not be used in interrupt context. The
1198 * mutex must be released by the same task that acquired it.
1199 */
1200int __sched mutex_trylock(struct mutex *lock)
1201{
1202 bool locked = __mutex_trylock(lock);
1203
1204 if (locked)
1205 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1206
1207 return locked;
1208}
1209EXPORT_SYMBOL(mutex_trylock);
1210
1211#ifndef CONFIG_DEBUG_LOCK_ALLOC
1212int __sched
1213ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1214{
1215 might_sleep();
1216
1217 if (__mutex_trylock_fast(&lock->base)) {
1218 if (ctx)
1219 ww_mutex_set_context_fastpath(lock, ctx);
1220 return 0;
1221 }
1222
1223 return __ww_mutex_lock_slowpath(lock, ctx);
1224}
1225EXPORT_SYMBOL(ww_mutex_lock);
1226
1227int __sched
1228ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1229{
1230 might_sleep();
1231
1232 if (__mutex_trylock_fast(&lock->base)) {
1233 if (ctx)
1234 ww_mutex_set_context_fastpath(lock, ctx);
1235 return 0;
1236 }
1237
1238 return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1239}
1240EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1241
1242#endif
1243
1244/**
1245 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1246 * @cnt: the atomic which we are to dec
1247 * @lock: the mutex to return holding if we dec to 0
1248 *
1249 * return true and hold lock if we dec to 0, return false otherwise
1250 */
1251int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1252{
1253 /* dec if we can't possibly hit 0 */
1254 if (atomic_add_unless(cnt, -1, 1))
1255 return 0;
1256 /* we might hit 0, so take the lock */
1257 mutex_lock(lock);
1258 if (!atomic_dec_and_test(cnt)) {
1259 /* when we actually did the dec, we didn't hit 0 */
1260 mutex_unlock(lock);
1261 return 0;
1262 }
1263 /* we hit 0, and we hold the lock */
1264 return 1;
1265}
1266EXPORT_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);