Line data Source code
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 :
39 : void
40 75281 : __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
41 : {
42 75281 : atomic_long_set(&lock->owner, 0);
43 75281 : spin_lock_init(&lock->wait_lock);
44 75281 : INIT_LIST_HEAD(&lock->wait_list);
45 : #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
46 75281 : osq_lock_init(&lock->osq);
47 : #endif
48 :
49 75281 : debug_mutex_init(lock, name, key);
50 75282 : }
51 : EXPORT_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 : */
73 114908 : static inline struct task_struct *__mutex_owner(struct mutex *lock)
74 : {
75 229816 : return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
76 : }
77 :
78 129222 : static inline struct task_struct *__owner_task(unsigned long owner)
79 : {
80 129222 : return (struct task_struct *)(owner & ~MUTEX_FLAGS);
81 : }
82 :
83 413 : bool mutex_is_locked(struct mutex *lock)
84 : {
85 413 : return __mutex_owner(lock) != NULL;
86 : }
87 : EXPORT_SYMBOL(mutex_is_locked);
88 :
89 257617 : static inline unsigned long __owner_flags(unsigned long owner)
90 : {
91 257617 : return owner & MUTEX_FLAGS;
92 : }
93 :
94 : /*
95 : * Trylock variant that retuns the owning task on failure.
96 : */
97 129218 : static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
98 : {
99 129218 : unsigned long owner, curr = (unsigned long)current;
100 :
101 129218 : owner = atomic_long_read(&lock->owner);
102 129274 : for (;;) { /* must loop, can race against a flag */
103 129274 : unsigned long old, flags = __owner_flags(owner);
104 129274 : unsigned long task = owner & ~MUTEX_FLAGS;
105 :
106 129274 : if (task) {
107 878 : if (likely(task != curr))
108 : break;
109 :
110 0 : if (likely(!(flags & MUTEX_FLAG_PICKUP)))
111 : break;
112 :
113 0 : flags &= ~MUTEX_FLAG_PICKUP;
114 : } else {
115 : #ifdef CONFIG_DEBUG_MUTEXES
116 128396 : DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
117 : #endif
118 : }
119 :
120 : /*
121 : * We set the HANDOFF bit, we must make sure it doesn't live
122 : * past the point where we acquire it. This would be possible
123 : * if we (accidentally) set the bit on an unlocked mutex.
124 : */
125 128396 : flags &= ~MUTEX_FLAG_HANDOFF;
126 :
127 128396 : old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
128 128424 : if (old == owner)
129 : return NULL;
130 :
131 : owner = old;
132 : }
133 :
134 878 : return __owner_task(owner);
135 : }
136 :
137 : /*
138 : * Actual trylock that will work on any unlocked state.
139 : */
140 128418 : static inline bool __mutex_trylock(struct mutex *lock)
141 : {
142 128138 : return !__mutex_trylock_or_owner(lock);
143 : }
144 :
145 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
146 : /*
147 : * Lockdep annotations are contained to the slow paths for simplicity.
148 : * There is nothing that would stop spreading the lockdep annotations outwards
149 : * except more code.
150 : */
151 :
152 : /*
153 : * Optimistic trylock that only works in the uncontended case. Make sure to
154 : * follow with a __mutex_trylock() before failing.
155 : */
156 : static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
157 : {
158 : unsigned long curr = (unsigned long)current;
159 : unsigned long zero = 0UL;
160 :
161 : if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
162 : return true;
163 :
164 : return false;
165 : }
166 :
167 : static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
168 : {
169 : unsigned long curr = (unsigned long)current;
170 :
171 : if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
172 : return true;
173 :
174 : return false;
175 : }
176 : #endif
177 :
178 45 : static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
179 : {
180 45 : atomic_long_or(flag, &lock->owner);
181 45 : }
182 :
183 23 : static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
184 : {
185 23 : atomic_long_andnot(flag, &lock->owner);
186 23 : }
187 :
188 45 : static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
189 : {
190 45 : return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
191 : }
192 :
193 : /*
194 : * Add @waiter to a given location in the lock wait_list and set the
195 : * FLAG_WAITERS flag if it's the first waiter.
196 : */
197 : static void __sched
198 23 : __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
199 : struct list_head *list)
200 : {
201 23 : debug_mutex_add_waiter(lock, waiter, current);
202 :
203 23 : list_add_tail(&waiter->list, list);
204 23 : if (__mutex_waiter_is_first(lock, waiter))
205 23 : __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
206 23 : }
207 :
208 : /*
209 : * Give up ownership to a specific task, when @task = NULL, this is equivalent
210 : * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
211 : * WAITERS. Provides RELEASE semantics like a regular unlock, the
212 : * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
213 : */
214 0 : static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
215 : {
216 0 : unsigned long owner = atomic_long_read(&lock->owner);
217 :
218 0 : for (;;) {
219 0 : unsigned long old, new;
220 :
221 : #ifdef CONFIG_DEBUG_MUTEXES
222 0 : DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
223 0 : DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
224 : #endif
225 :
226 0 : new = (owner & MUTEX_FLAG_WAITERS);
227 0 : new |= (unsigned long)task;
228 0 : if (task)
229 0 : new |= MUTEX_FLAG_PICKUP;
230 :
231 0 : old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
232 0 : if (old == owner)
233 : break;
234 :
235 : owner = old;
236 : }
237 0 : }
238 :
239 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
240 : /*
241 : * We split the mutex lock/unlock logic into separate fastpath and
242 : * slowpath functions, to reduce the register pressure on the fastpath.
243 : * We also put the fastpath first in the kernel image, to make sure the
244 : * branch is predicted by the CPU as default-untaken.
245 : */
246 : static void __sched __mutex_lock_slowpath(struct mutex *lock);
247 :
248 : /**
249 : * mutex_lock - acquire the mutex
250 : * @lock: the mutex to be acquired
251 : *
252 : * Lock the mutex exclusively for this task. If the mutex is not
253 : * available right now, it will sleep until it can get it.
254 : *
255 : * The mutex must later on be released by the same task that
256 : * acquired it. Recursive locking is not allowed. The task
257 : * may not exit without first unlocking the mutex. Also, kernel
258 : * memory where the mutex resides must not be freed with
259 : * the mutex still locked. The mutex must first be initialized
260 : * (or statically defined) before it can be locked. memset()-ing
261 : * the mutex to 0 is not allowed.
262 : *
263 : * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
264 : * checks that will enforce the restrictions and will also do
265 : * deadlock debugging)
266 : *
267 : * This function is similar to (but not equivalent to) down().
268 : */
269 : void __sched mutex_lock(struct mutex *lock)
270 : {
271 : might_sleep();
272 :
273 : if (!__mutex_trylock_fast(lock))
274 : __mutex_lock_slowpath(lock);
275 : }
276 : EXPORT_SYMBOL(mutex_lock);
277 : #endif
278 :
279 : /*
280 : * Wait-Die:
281 : * The newer transactions are killed when:
282 : * It (the new transaction) makes a request for a lock being held
283 : * by an older transaction.
284 : *
285 : * Wound-Wait:
286 : * The newer transactions are wounded when:
287 : * An older transaction makes a request for a lock being held by
288 : * the newer transaction.
289 : */
290 :
291 : /*
292 : * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
293 : * it.
294 : */
295 : static __always_inline void
296 0 : ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
297 : {
298 : #ifdef CONFIG_DEBUG_MUTEXES
299 : /*
300 : * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
301 : * but released with a normal mutex_unlock in this call.
302 : *
303 : * This should never happen, always use ww_mutex_unlock.
304 : */
305 0 : DEBUG_LOCKS_WARN_ON(ww->ctx);
306 :
307 : /*
308 : * Not quite done after calling ww_acquire_done() ?
309 : */
310 0 : DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
311 :
312 0 : if (ww_ctx->contending_lock) {
313 : /*
314 : * After -EDEADLK you tried to
315 : * acquire a different ww_mutex? Bad!
316 : */
317 0 : DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
318 :
319 : /*
320 : * You called ww_mutex_lock after receiving -EDEADLK,
321 : * but 'forgot' to unlock everything else first?
322 : */
323 0 : DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
324 0 : ww_ctx->contending_lock = NULL;
325 : }
326 :
327 : /*
328 : * Naughty, using a different class will lead to undefined behavior!
329 : */
330 0 : DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
331 : #endif
332 0 : ww_ctx->acquired++;
333 0 : ww->ctx = ww_ctx;
334 0 : }
335 :
336 : /*
337 : * Determine if context @a is 'after' context @b. IOW, @a is a younger
338 : * transaction than @b and depending on algorithm either needs to wait for
339 : * @b or die.
340 : */
341 : static inline bool __sched
342 0 : __ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
343 : {
344 :
345 0 : return (signed long)(a->stamp - b->stamp) > 0;
346 : }
347 :
348 : /*
349 : * Wait-Die; wake a younger waiter context (when locks held) such that it can
350 : * die.
351 : *
352 : * Among waiters with context, only the first one can have other locks acquired
353 : * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
354 : * __ww_mutex_check_kill() wake any but the earliest context.
355 : */
356 : static bool __sched
357 0 : __ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
358 : struct ww_acquire_ctx *ww_ctx)
359 : {
360 0 : if (!ww_ctx->is_wait_die)
361 : return false;
362 :
363 0 : if (waiter->ww_ctx->acquired > 0 &&
364 0 : __ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
365 0 : debug_mutex_wake_waiter(lock, waiter);
366 0 : wake_up_process(waiter->task);
367 : }
368 :
369 : return true;
370 : }
371 :
372 : /*
373 : * Wound-Wait; wound a younger @hold_ctx if it holds the lock.
374 : *
375 : * Wound the lock holder if there are waiters with older transactions than
376 : * the lock holders. Even if multiple waiters may wound the lock holder,
377 : * it's sufficient that only one does.
378 : */
379 0 : static bool __ww_mutex_wound(struct mutex *lock,
380 : struct ww_acquire_ctx *ww_ctx,
381 : struct ww_acquire_ctx *hold_ctx)
382 : {
383 0 : struct task_struct *owner = __mutex_owner(lock);
384 :
385 0 : lockdep_assert_held(&lock->wait_lock);
386 :
387 : /*
388 : * Possible through __ww_mutex_add_waiter() when we race with
389 : * ww_mutex_set_context_fastpath(). In that case we'll get here again
390 : * through __ww_mutex_check_waiters().
391 : */
392 0 : if (!hold_ctx)
393 : return false;
394 :
395 : /*
396 : * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
397 : * it cannot go away because we'll have FLAG_WAITERS set and hold
398 : * wait_lock.
399 : */
400 0 : if (!owner)
401 : return false;
402 :
403 0 : if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
404 0 : hold_ctx->wounded = 1;
405 :
406 : /*
407 : * wake_up_process() paired with set_current_state()
408 : * inserts sufficient barriers to make sure @owner either sees
409 : * it's wounded in __ww_mutex_check_kill() or has a
410 : * wakeup pending to re-read the wounded state.
411 : */
412 0 : if (owner != current)
413 0 : wake_up_process(owner);
414 :
415 0 : return true;
416 : }
417 :
418 : return false;
419 : }
420 :
421 : /*
422 : * We just acquired @lock under @ww_ctx, if there are later contexts waiting
423 : * behind us on the wait-list, check if they need to die, or wound us.
424 : *
425 : * See __ww_mutex_add_waiter() for the list-order construction; basically the
426 : * list is ordered by stamp, smallest (oldest) first.
427 : *
428 : * This relies on never mixing wait-die/wound-wait on the same wait-list;
429 : * which is currently ensured by that being a ww_class property.
430 : *
431 : * The current task must not be on the wait list.
432 : */
433 : static void __sched
434 0 : __ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
435 : {
436 0 : struct mutex_waiter *cur;
437 :
438 0 : lockdep_assert_held(&lock->wait_lock);
439 :
440 0 : list_for_each_entry(cur, &lock->wait_list, list) {
441 0 : if (!cur->ww_ctx)
442 0 : continue;
443 :
444 0 : if (__ww_mutex_die(lock, cur, ww_ctx) ||
445 0 : __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
446 : break;
447 : }
448 0 : }
449 :
450 : /*
451 : * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
452 : * and wake up any waiters so they can recheck.
453 : */
454 : static __always_inline void
455 0 : ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
456 : {
457 0 : ww_mutex_lock_acquired(lock, ctx);
458 :
459 : /*
460 : * The lock->ctx update should be visible on all cores before
461 : * the WAITERS check is done, otherwise contended waiters might be
462 : * missed. The contended waiters will either see ww_ctx == NULL
463 : * and keep spinning, or it will acquire wait_lock, add itself
464 : * to waiter list and sleep.
465 : */
466 0 : smp_mb(); /* See comments above and below. */
467 :
468 : /*
469 : * [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
470 : * MB MB
471 : * [R] MUTEX_FLAG_WAITERS [R] ww->ctx
472 : *
473 : * The memory barrier above pairs with the memory barrier in
474 : * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
475 : * and/or !empty list.
476 : */
477 0 : if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
478 : return;
479 :
480 : /*
481 : * Uh oh, we raced in fastpath, check if any of the waiters need to
482 : * die or wound us.
483 : */
484 0 : spin_lock(&lock->base.wait_lock);
485 0 : __ww_mutex_check_waiters(&lock->base, ctx);
486 0 : spin_unlock(&lock->base.wait_lock);
487 : }
488 :
489 : #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
490 :
491 : static inline
492 0 : bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
493 : struct mutex_waiter *waiter)
494 : {
495 0 : struct ww_mutex *ww;
496 :
497 0 : ww = container_of(lock, struct ww_mutex, base);
498 :
499 : /*
500 : * If ww->ctx is set the contents are undefined, only
501 : * by acquiring wait_lock there is a guarantee that
502 : * they are not invalid when reading.
503 : *
504 : * As such, when deadlock detection needs to be
505 : * performed the optimistic spinning cannot be done.
506 : *
507 : * Check this in every inner iteration because we may
508 : * be racing against another thread's ww_mutex_lock.
509 : */
510 0 : if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
511 : return false;
512 :
513 : /*
514 : * If we aren't on the wait list yet, cancel the spin
515 : * if there are waiters. We want to avoid stealing the
516 : * lock from a waiter with an earlier stamp, since the
517 : * other thread may already own a lock that we also
518 : * need.
519 : */
520 0 : if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
521 : return false;
522 :
523 : /*
524 : * Similarly, stop spinning if we are no longer the
525 : * first waiter.
526 : */
527 0 : if (waiter && !__mutex_waiter_is_first(lock, waiter))
528 0 : return false;
529 :
530 : return true;
531 : }
532 :
533 : /*
534 : * Look out! "owner" is an entirely speculative pointer access and not
535 : * reliable.
536 : *
537 : * "noinline" so that this function shows up on perf profiles.
538 : */
539 : static noinline
540 221 : bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
541 : struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
542 : {
543 221 : bool ret = true;
544 :
545 221 : rcu_read_lock();
546 113892 : while (__mutex_owner(lock) == owner) {
547 : /*
548 : * Ensure we emit the owner->on_cpu, dereference _after_
549 : * checking lock->owner still matches owner. If that fails,
550 : * owner might point to freed memory. If it still matches,
551 : * the rcu_read_lock() ensures the memory stays valid.
552 : */
553 113680 : barrier();
554 :
555 : /*
556 : * Use vcpu_is_preempted to detect lock holder preemption issue.
557 : */
558 341034 : if (!owner->on_cpu || need_resched() ||
559 113676 : vcpu_is_preempted(task_cpu(owner))) {
560 : ret = false;
561 : break;
562 : }
563 :
564 113671 : if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
565 : ret = false;
566 : break;
567 : }
568 :
569 113671 : cpu_relax();
570 : }
571 221 : rcu_read_unlock();
572 :
573 221 : return ret;
574 : }
575 :
576 : /*
577 : * Initial check for entering the mutex spinning loop
578 : */
579 612 : static inline int mutex_can_spin_on_owner(struct mutex *lock)
580 : {
581 612 : struct task_struct *owner;
582 612 : int retval = 1;
583 :
584 612 : if (need_resched())
585 : return 0;
586 :
587 603 : rcu_read_lock();
588 603 : owner = __mutex_owner(lock);
589 :
590 : /*
591 : * As lock holder preemption issue, we both skip spinning if task is not
592 : * on cpu or its cpu is preempted
593 : */
594 603 : if (owner)
595 272 : retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
596 603 : rcu_read_unlock();
597 :
598 : /*
599 : * If lock->owner is not set, the mutex has been released. Return true
600 : * such that we'll trylock in the spin path, which is a faster option
601 : * than the blocking slow path.
602 : */
603 603 : return retval;
604 : }
605 :
606 : /*
607 : * Optimistic spinning.
608 : *
609 : * We try to spin for acquisition when we find that the lock owner
610 : * is currently running on a (different) CPU and while we don't
611 : * need to reschedule. The rationale is that if the lock owner is
612 : * running, it is likely to release the lock soon.
613 : *
614 : * The mutex spinners are queued up using MCS lock so that only one
615 : * spinner can compete for the mutex. However, if mutex spinning isn't
616 : * going to happen, there is no point in going through the lock/unlock
617 : * overhead.
618 : *
619 : * Returns true when the lock was taken, otherwise false, indicating
620 : * that we need to jump to the slowpath and sleep.
621 : *
622 : * The waiter flag is set to true if the spinner is a waiter in the wait
623 : * queue. The waiter-spinner will spin on the lock directly and concurrently
624 : * with the spinner at the head of the OSQ, if present, until the owner is
625 : * changed to itself.
626 : */
627 : static __always_inline bool
628 612 : mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
629 : const bool use_ww_ctx, struct mutex_waiter *waiter)
630 : {
631 612 : if (!waiter) {
632 : /*
633 : * The purpose of the mutex_can_spin_on_owner() function is
634 : * to eliminate the overhead of osq_lock() and osq_unlock()
635 : * in case spinning isn't possible. As a waiter-spinner
636 : * is not going to take OSQ lock anyway, there is no need
637 : * to call mutex_can_spin_on_owner().
638 : */
639 612 : if (!mutex_can_spin_on_owner(lock))
640 24 : goto fail;
641 :
642 : /*
643 : * In order to avoid a stampede of mutex spinners trying to
644 : * acquire the mutex all at once, the spinners need to take a
645 : * MCS (queued) lock first before spinning on the owner field.
646 : */
647 588 : if (!osq_lock(&lock->osq))
648 0 : goto fail;
649 : }
650 :
651 800 : for (;;) {
652 800 : struct task_struct *owner;
653 :
654 : /* Try to acquire the mutex... */
655 800 : owner = __mutex_trylock_or_owner(lock);
656 800 : if (!owner)
657 : break;
658 :
659 : /*
660 : * There's an owner, wait for it to either
661 : * release the lock or go to sleep.
662 : */
663 221 : if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
664 9 : goto fail_unlock;
665 :
666 : /*
667 : * The cpu_relax() call is a compiler barrier which forces
668 : * everything in this loop to be re-loaded. We don't need
669 : * memory barriers as we'll eventually observe the right
670 : * values at the cost of a few extra spins.
671 : */
672 212 : cpu_relax();
673 : }
674 :
675 579 : if (!waiter)
676 579 : osq_unlock(&lock->osq);
677 :
678 : return true;
679 :
680 :
681 9 : fail_unlock:
682 9 : if (!waiter)
683 9 : osq_unlock(&lock->osq);
684 :
685 33 : fail:
686 : /*
687 : * If we fell out of the spin path because of need_resched(),
688 : * reschedule now, before we try-lock the mutex. This avoids getting
689 : * scheduled out right after we obtained the mutex.
690 : */
691 33 : if (need_resched()) {
692 : /*
693 : * We _should_ have TASK_RUNNING here, but just in case
694 : * we do not, make it so, otherwise we might get stuck.
695 : */
696 11 : __set_current_state(TASK_RUNNING);
697 11 : schedule_preempt_disabled();
698 : }
699 :
700 : return false;
701 : }
702 : #else
703 : static __always_inline bool
704 : mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
705 : const bool use_ww_ctx, struct mutex_waiter *waiter)
706 : {
707 : return false;
708 : }
709 : #endif
710 :
711 : static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
712 :
713 : /**
714 : * mutex_unlock - release the mutex
715 : * @lock: the mutex to be released
716 : *
717 : * Unlock a mutex that has been locked by this task previously.
718 : *
719 : * This function must not be used in interrupt context. Unlocking
720 : * of a not locked mutex is not allowed.
721 : *
722 : * This function is similar to (but not equivalent to) up().
723 : */
724 128348 : void __sched mutex_unlock(struct mutex *lock)
725 : {
726 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
727 : if (__mutex_unlock_fast(lock))
728 : return;
729 : #endif
730 128348 : __mutex_unlock_slowpath(lock, _RET_IP_);
731 128358 : }
732 : EXPORT_SYMBOL(mutex_unlock);
733 :
734 : /**
735 : * ww_mutex_unlock - release the w/w mutex
736 : * @lock: the mutex to be released
737 : *
738 : * Unlock a mutex that has been locked by this task previously with any of the
739 : * ww_mutex_lock* functions (with or without an acquire context). It is
740 : * forbidden to release the locks after releasing the acquire context.
741 : *
742 : * This function must not be used in interrupt context. Unlocking
743 : * of a unlocked mutex is not allowed.
744 : */
745 0 : void __sched ww_mutex_unlock(struct ww_mutex *lock)
746 : {
747 : /*
748 : * The unlocking fastpath is the 0->1 transition from 'locked'
749 : * into 'unlocked' state:
750 : */
751 0 : if (lock->ctx) {
752 : #ifdef CONFIG_DEBUG_MUTEXES
753 0 : DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
754 : #endif
755 0 : if (lock->ctx->acquired > 0)
756 0 : lock->ctx->acquired--;
757 0 : lock->ctx = NULL;
758 : }
759 :
760 0 : mutex_unlock(&lock->base);
761 0 : }
762 : EXPORT_SYMBOL(ww_mutex_unlock);
763 :
764 :
765 : static __always_inline int __sched
766 0 : __ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
767 : {
768 0 : if (ww_ctx->acquired > 0) {
769 : #ifdef CONFIG_DEBUG_MUTEXES
770 0 : struct ww_mutex *ww;
771 :
772 0 : ww = container_of(lock, struct ww_mutex, base);
773 0 : DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
774 0 : ww_ctx->contending_lock = ww;
775 : #endif
776 0 : return -EDEADLK;
777 : }
778 :
779 : return 0;
780 : }
781 :
782 :
783 : /*
784 : * Check the wound condition for the current lock acquire.
785 : *
786 : * Wound-Wait: If we're wounded, kill ourself.
787 : *
788 : * Wait-Die: If we're trying to acquire a lock already held by an older
789 : * context, kill ourselves.
790 : *
791 : * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
792 : * look at waiters before us in the wait-list.
793 : */
794 : static inline int __sched
795 0 : __ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
796 : struct ww_acquire_ctx *ctx)
797 : {
798 0 : struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
799 0 : struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
800 0 : struct mutex_waiter *cur;
801 :
802 0 : if (ctx->acquired == 0)
803 : return 0;
804 :
805 0 : if (!ctx->is_wait_die) {
806 0 : if (ctx->wounded)
807 0 : return __ww_mutex_kill(lock, ctx);
808 :
809 : return 0;
810 : }
811 :
812 0 : if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
813 0 : return __ww_mutex_kill(lock, ctx);
814 :
815 : /*
816 : * If there is a waiter in front of us that has a context, then its
817 : * stamp is earlier than ours and we must kill ourself.
818 : */
819 0 : cur = waiter;
820 0 : list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
821 0 : if (!cur->ww_ctx)
822 0 : continue;
823 :
824 0 : return __ww_mutex_kill(lock, ctx);
825 : }
826 :
827 : return 0;
828 : }
829 :
830 : /*
831 : * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
832 : * first. Such that older contexts are preferred to acquire the lock over
833 : * younger contexts.
834 : *
835 : * Waiters without context are interspersed in FIFO order.
836 : *
837 : * Furthermore, for Wait-Die kill ourself immediately when possible (there are
838 : * older contexts already waiting) to avoid unnecessary waiting and for
839 : * Wound-Wait ensure we wound the owning context when it is younger.
840 : */
841 : static inline int __sched
842 0 : __ww_mutex_add_waiter(struct mutex_waiter *waiter,
843 : struct mutex *lock,
844 : struct ww_acquire_ctx *ww_ctx)
845 : {
846 0 : struct mutex_waiter *cur;
847 0 : struct list_head *pos;
848 0 : bool is_wait_die;
849 :
850 0 : if (!ww_ctx) {
851 0 : __mutex_add_waiter(lock, waiter, &lock->wait_list);
852 0 : return 0;
853 : }
854 :
855 0 : is_wait_die = ww_ctx->is_wait_die;
856 :
857 : /*
858 : * Add the waiter before the first waiter with a higher stamp.
859 : * Waiters without a context are skipped to avoid starving
860 : * them. Wait-Die waiters may die here. Wound-Wait waiters
861 : * never die here, but they are sorted in stamp order and
862 : * may wound the lock holder.
863 : */
864 0 : pos = &lock->wait_list;
865 0 : list_for_each_entry_reverse(cur, &lock->wait_list, list) {
866 0 : if (!cur->ww_ctx)
867 0 : continue;
868 :
869 0 : if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
870 : /*
871 : * Wait-Die: if we find an older context waiting, there
872 : * is no point in queueing behind it, as we'd have to
873 : * die the moment it would acquire the lock.
874 : */
875 0 : if (is_wait_die) {
876 0 : int ret = __ww_mutex_kill(lock, ww_ctx);
877 :
878 0 : if (ret)
879 0 : return ret;
880 : }
881 :
882 : break;
883 : }
884 :
885 0 : pos = &cur->list;
886 :
887 : /* Wait-Die: ensure younger waiters die. */
888 0 : __ww_mutex_die(lock, cur, ww_ctx);
889 : }
890 :
891 0 : __mutex_add_waiter(lock, waiter, pos);
892 :
893 : /*
894 : * Wound-Wait: if we're blocking on a mutex owned by a younger context,
895 : * wound that such that we might proceed.
896 : */
897 0 : if (!is_wait_die) {
898 0 : struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
899 :
900 : /*
901 : * See ww_mutex_set_context_fastpath(). Orders setting
902 : * MUTEX_FLAG_WAITERS vs the ww->ctx load,
903 : * such that either we or the fastpath will wound @ww->ctx.
904 : */
905 0 : smp_mb();
906 0 : __ww_mutex_wound(lock, ww_ctx, ww->ctx);
907 : }
908 :
909 : return 0;
910 : }
911 :
912 : /*
913 : * Lock a mutex (possibly interruptible), slowpath:
914 : */
915 : static __always_inline int __sched
916 128068 : __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
917 : struct lockdep_map *nest_lock, unsigned long ip,
918 : struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
919 : {
920 128068 : struct mutex_waiter waiter;
921 128068 : bool first = false;
922 128068 : struct ww_mutex *ww;
923 128068 : int ret;
924 :
925 256142 : might_sleep();
926 :
927 : #ifdef CONFIG_DEBUG_MUTEXES
928 128074 : DEBUG_LOCKS_WARN_ON(lock->magic != lock);
929 : #endif
930 :
931 128074 : ww = container_of(lock, struct ww_mutex, base);
932 0 : if (use_ww_ctx && ww_ctx) {
933 0 : if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
934 : return -EALREADY;
935 :
936 : /*
937 : * Reset the wounded flag after a kill. No other process can
938 : * race and wound us here since they can't have a valid owner
939 : * pointer if we don't have any locks held.
940 : */
941 0 : if (ww_ctx->acquired == 0)
942 0 : ww_ctx->wounded = 0;
943 : }
944 :
945 128074 : preempt_disable();
946 128074 : mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
947 :
948 128062 : if (__mutex_trylock(lock) ||
949 1202 : mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
950 : /* got the lock, yay! */
951 128046 : lock_acquired(&lock->dep_map, ip);
952 0 : if (use_ww_ctx && ww_ctx)
953 0 : ww_mutex_set_context_fastpath(ww, ww_ctx);
954 128046 : preempt_enable();
955 128050 : return 0;
956 : }
957 :
958 33 : spin_lock(&lock->wait_lock);
959 : /*
960 : * After waiting to acquire the wait_lock, try again.
961 : */
962 33 : if (__mutex_trylock(lock)) {
963 0 : if (use_ww_ctx && ww_ctx)
964 0 : __ww_mutex_check_waiters(lock, ww_ctx);
965 :
966 10 : goto skip_wait;
967 : }
968 :
969 23 : debug_mutex_lock_common(lock, &waiter);
970 :
971 23 : lock_contended(&lock->dep_map, ip);
972 :
973 23 : if (!use_ww_ctx) {
974 : /* add waiting tasks to the end of the waitqueue (FIFO): */
975 23 : __mutex_add_waiter(lock, &waiter, &lock->wait_list);
976 :
977 :
978 : #ifdef CONFIG_DEBUG_MUTEXES
979 23 : waiter.ww_ctx = MUTEX_POISON_WW_CTX;
980 : #endif
981 : } else {
982 : /*
983 : * Add in stamp order, waking up waiters that must kill
984 : * themselves.
985 : */
986 0 : ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
987 0 : if (ret)
988 0 : goto err_early_kill;
989 :
990 0 : waiter.ww_ctx = ww_ctx;
991 : }
992 :
993 23 : waiter.task = current;
994 :
995 23 : set_current_state(state);
996 23 : for (;;) {
997 : /*
998 : * Once we hold wait_lock, we're serialized against
999 : * mutex_unlock() handing the lock off to us, do a trylock
1000 : * before testing the error conditions to make sure we pick up
1001 : * the handoff.
1002 : */
1003 23 : if (__mutex_trylock(lock))
1004 1 : goto acquired;
1005 :
1006 : /*
1007 : * Check for signals and kill conditions while holding
1008 : * wait_lock. This ensures the lock cancellation is ordered
1009 : * against mutex_unlock() and wake-ups do not go missing.
1010 : */
1011 22 : if (signal_pending_state(state, current)) {
1012 0 : ret = -EINTR;
1013 0 : goto err;
1014 : }
1015 :
1016 0 : if (use_ww_ctx && ww_ctx) {
1017 0 : ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
1018 0 : if (ret)
1019 0 : goto err;
1020 : }
1021 :
1022 22 : spin_unlock(&lock->wait_lock);
1023 22 : schedule_preempt_disabled();
1024 :
1025 : /*
1026 : * ww_mutex needs to always recheck its position since its waiter
1027 : * list is not FIFO ordered.
1028 : */
1029 22 : if ((use_ww_ctx && ww_ctx) || !first) {
1030 22 : first = __mutex_waiter_is_first(lock, &waiter);
1031 22 : if (first)
1032 22 : __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
1033 : }
1034 :
1035 22 : set_current_state(state);
1036 : /*
1037 : * Here we order against unlock; we must either see it change
1038 : * state back to RUNNING and fall through the next schedule(),
1039 : * or we must see its unlock and acquire.
1040 : */
1041 22 : if (__mutex_trylock(lock) ||
1042 0 : (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
1043 : break;
1044 :
1045 23 : spin_lock(&lock->wait_lock);
1046 : }
1047 22 : spin_lock(&lock->wait_lock);
1048 23 : acquired:
1049 23 : __set_current_state(TASK_RUNNING);
1050 :
1051 0 : if (use_ww_ctx && ww_ctx) {
1052 : /*
1053 : * Wound-Wait; we stole the lock (!first_waiter), check the
1054 : * waiters as anyone might want to wound us.
1055 : */
1056 0 : if (!ww_ctx->is_wait_die &&
1057 0 : !__mutex_waiter_is_first(lock, &waiter))
1058 0 : __ww_mutex_check_waiters(lock, ww_ctx);
1059 : }
1060 :
1061 23 : mutex_remove_waiter(lock, &waiter, current);
1062 23 : if (likely(list_empty(&lock->wait_list)))
1063 23 : __mutex_clear_flag(lock, MUTEX_FLAGS);
1064 :
1065 23 : debug_mutex_free_waiter(&waiter);
1066 :
1067 33 : skip_wait:
1068 : /* got the lock - cleanup and rejoice! */
1069 33 : lock_acquired(&lock->dep_map, ip);
1070 :
1071 0 : if (use_ww_ctx && ww_ctx)
1072 0 : ww_mutex_lock_acquired(ww, ww_ctx);
1073 :
1074 33 : spin_unlock(&lock->wait_lock);
1075 33 : preempt_enable();
1076 33 : return 0;
1077 :
1078 0 : err:
1079 0 : __set_current_state(TASK_RUNNING);
1080 0 : mutex_remove_waiter(lock, &waiter, current);
1081 0 : err_early_kill:
1082 0 : spin_unlock(&lock->wait_lock);
1083 0 : debug_mutex_free_waiter(&waiter);
1084 0 : mutex_release(&lock->dep_map, ip);
1085 0 : preempt_enable();
1086 0 : return ret;
1087 : }
1088 :
1089 : static int __sched
1090 128067 : __mutex_lock(struct mutex *lock, long state, unsigned int subclass,
1091 : struct lockdep_map *nest_lock, unsigned long ip)
1092 : {
1093 128067 : return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
1094 : }
1095 :
1096 : static int __sched
1097 0 : __ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
1098 : struct lockdep_map *nest_lock, unsigned long ip,
1099 : struct ww_acquire_ctx *ww_ctx)
1100 : {
1101 0 : return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
1102 : }
1103 :
1104 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
1105 : void __sched
1106 124027 : mutex_lock_nested(struct mutex *lock, unsigned int subclass)
1107 : {
1108 124027 : __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
1109 124043 : }
1110 :
1111 : EXPORT_SYMBOL_GPL(mutex_lock_nested);
1112 :
1113 : void __sched
1114 0 : _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
1115 : {
1116 0 : __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
1117 0 : }
1118 : EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
1119 :
1120 : int __sched
1121 2206 : mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
1122 : {
1123 2206 : return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
1124 : }
1125 : EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
1126 :
1127 : int __sched
1128 1833 : mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
1129 : {
1130 1833 : return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
1131 : }
1132 : EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
1133 :
1134 : void __sched
1135 1 : mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
1136 : {
1137 1 : int token;
1138 :
1139 1 : might_sleep();
1140 :
1141 1 : token = io_schedule_prepare();
1142 1 : __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
1143 1 : subclass, NULL, _RET_IP_, NULL, 0);
1144 1 : io_schedule_finish(token);
1145 1 : }
1146 : EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
1147 :
1148 : static inline int
1149 0 : ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1150 : {
1151 : #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
1152 0 : unsigned tmp;
1153 :
1154 0 : if (ctx->deadlock_inject_countdown-- == 0) {
1155 0 : tmp = ctx->deadlock_inject_interval;
1156 0 : if (tmp > UINT_MAX/4)
1157 : tmp = UINT_MAX;
1158 : else
1159 0 : tmp = tmp*2 + tmp + tmp/2;
1160 :
1161 0 : ctx->deadlock_inject_interval = tmp;
1162 0 : ctx->deadlock_inject_countdown = tmp;
1163 0 : ctx->contending_lock = lock;
1164 :
1165 0 : ww_mutex_unlock(lock);
1166 :
1167 0 : return -EDEADLK;
1168 : }
1169 : #endif
1170 :
1171 : return 0;
1172 : }
1173 :
1174 : int __sched
1175 0 : ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1176 : {
1177 0 : int ret;
1178 :
1179 0 : might_sleep();
1180 0 : ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
1181 0 : 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
1182 : ctx);
1183 0 : if (!ret && ctx && ctx->acquired > 1)
1184 0 : return ww_mutex_deadlock_injection(lock, ctx);
1185 :
1186 : return ret;
1187 : }
1188 : EXPORT_SYMBOL_GPL(ww_mutex_lock);
1189 :
1190 : int __sched
1191 0 : ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1192 : {
1193 0 : int ret;
1194 :
1195 0 : might_sleep();
1196 0 : ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
1197 0 : 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
1198 : ctx);
1199 :
1200 0 : if (!ret && ctx && ctx->acquired > 1)
1201 0 : return ww_mutex_deadlock_injection(lock, ctx);
1202 :
1203 : return ret;
1204 : }
1205 : EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
1206 :
1207 : #endif
1208 :
1209 : /*
1210 : * Release the lock, slowpath:
1211 : */
1212 128352 : static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
1213 : {
1214 128352 : struct task_struct *next = NULL;
1215 128352 : DEFINE_WAKE_Q(wake_q);
1216 128352 : unsigned long owner;
1217 :
1218 128352 : mutex_release(&lock->dep_map, ip);
1219 :
1220 : /*
1221 : * Release the lock before (potentially) taking the spinlock such that
1222 : * other contenders can get on with things ASAP.
1223 : *
1224 : * Except when HANDOFF, in that case we must not clear the owner field,
1225 : * but instead set it to the top waiter.
1226 : */
1227 128343 : owner = atomic_long_read(&lock->owner);
1228 128343 : for (;;) {
1229 128343 : unsigned long old;
1230 :
1231 : #ifdef CONFIG_DEBUG_MUTEXES
1232 128343 : DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
1233 128343 : DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
1234 : #endif
1235 :
1236 128343 : if (owner & MUTEX_FLAG_HANDOFF)
1237 : break;
1238 :
1239 256700 : old = atomic_long_cmpxchg_release(&lock->owner, owner,
1240 128343 : __owner_flags(owner));
1241 128357 : if (old == owner) {
1242 128357 : if (owner & MUTEX_FLAG_WAITERS)
1243 : break;
1244 :
1245 128203 : return;
1246 : }
1247 :
1248 : owner = old;
1249 : }
1250 :
1251 154 : spin_lock(&lock->wait_lock);
1252 154 : debug_mutex_unlock(lock);
1253 154 : if (!list_empty(&lock->wait_list)) {
1254 : /* get the first entry from the wait-list: */
1255 154 : struct mutex_waiter *waiter =
1256 154 : list_first_entry(&lock->wait_list,
1257 : struct mutex_waiter, list);
1258 :
1259 154 : next = waiter->task;
1260 :
1261 154 : debug_mutex_wake_waiter(lock, waiter);
1262 154 : wake_q_add(&wake_q, next);
1263 : }
1264 :
1265 154 : if (owner & MUTEX_FLAG_HANDOFF)
1266 0 : __mutex_handoff(lock, next);
1267 :
1268 154 : spin_unlock(&lock->wait_lock);
1269 :
1270 154 : wake_up_q(&wake_q);
1271 : }
1272 :
1273 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
1274 : /*
1275 : * Here come the less common (and hence less performance-critical) APIs:
1276 : * mutex_lock_interruptible() and mutex_trylock().
1277 : */
1278 : static noinline int __sched
1279 : __mutex_lock_killable_slowpath(struct mutex *lock);
1280 :
1281 : static noinline int __sched
1282 : __mutex_lock_interruptible_slowpath(struct mutex *lock);
1283 :
1284 : /**
1285 : * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
1286 : * @lock: The mutex to be acquired.
1287 : *
1288 : * Lock the mutex like mutex_lock(). If a signal is delivered while the
1289 : * process is sleeping, this function will return without acquiring the
1290 : * mutex.
1291 : *
1292 : * Context: Process context.
1293 : * Return: 0 if the lock was successfully acquired or %-EINTR if a
1294 : * signal arrived.
1295 : */
1296 : int __sched mutex_lock_interruptible(struct mutex *lock)
1297 : {
1298 : might_sleep();
1299 :
1300 : if (__mutex_trylock_fast(lock))
1301 : return 0;
1302 :
1303 : return __mutex_lock_interruptible_slowpath(lock);
1304 : }
1305 :
1306 : EXPORT_SYMBOL(mutex_lock_interruptible);
1307 :
1308 : /**
1309 : * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
1310 : * @lock: The mutex to be acquired.
1311 : *
1312 : * Lock the mutex like mutex_lock(). If a signal which will be fatal to
1313 : * the current process is delivered while the process is sleeping, this
1314 : * function will return without acquiring the mutex.
1315 : *
1316 : * Context: Process context.
1317 : * Return: 0 if the lock was successfully acquired or %-EINTR if a
1318 : * fatal signal arrived.
1319 : */
1320 : int __sched mutex_lock_killable(struct mutex *lock)
1321 : {
1322 : might_sleep();
1323 :
1324 : if (__mutex_trylock_fast(lock))
1325 : return 0;
1326 :
1327 : return __mutex_lock_killable_slowpath(lock);
1328 : }
1329 : EXPORT_SYMBOL(mutex_lock_killable);
1330 :
1331 : /**
1332 : * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1333 : * @lock: The mutex to be acquired.
1334 : *
1335 : * Lock the mutex like mutex_lock(). While the task is waiting for this
1336 : * mutex, it will be accounted as being in the IO wait state by the
1337 : * scheduler.
1338 : *
1339 : * Context: Process context.
1340 : */
1341 : void __sched mutex_lock_io(struct mutex *lock)
1342 : {
1343 : int token;
1344 :
1345 : token = io_schedule_prepare();
1346 : mutex_lock(lock);
1347 : io_schedule_finish(token);
1348 : }
1349 : EXPORT_SYMBOL_GPL(mutex_lock_io);
1350 :
1351 : static noinline void __sched
1352 : __mutex_lock_slowpath(struct mutex *lock)
1353 : {
1354 : __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1355 : }
1356 :
1357 : static noinline int __sched
1358 : __mutex_lock_killable_slowpath(struct mutex *lock)
1359 : {
1360 : return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1361 : }
1362 :
1363 : static noinline int __sched
1364 : __mutex_lock_interruptible_slowpath(struct mutex *lock)
1365 : {
1366 : return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1367 : }
1368 :
1369 : static noinline int __sched
1370 : __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1371 : {
1372 : return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
1373 : _RET_IP_, ctx);
1374 : }
1375 :
1376 : static noinline int __sched
1377 : __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1378 : struct ww_acquire_ctx *ctx)
1379 : {
1380 : return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
1381 : _RET_IP_, ctx);
1382 : }
1383 :
1384 : #endif
1385 :
1386 : /**
1387 : * mutex_trylock - try to acquire the mutex, without waiting
1388 : * @lock: the mutex to be acquired
1389 : *
1390 : * Try to acquire the mutex atomically. Returns 1 if the mutex
1391 : * has been acquired successfully, and 0 on contention.
1392 : *
1393 : * NOTE: this function follows the spin_trylock() convention, so
1394 : * it is negated from the down_trylock() return values! Be careful
1395 : * about this when converting semaphore users to mutexes.
1396 : *
1397 : * This function must not be used in interrupt context. The
1398 : * mutex must be released by the same task that acquired it.
1399 : */
1400 279 : int __sched mutex_trylock(struct mutex *lock)
1401 : {
1402 279 : bool locked;
1403 :
1404 : #ifdef CONFIG_DEBUG_MUTEXES
1405 279 : DEBUG_LOCKS_WARN_ON(lock->magic != lock);
1406 : #endif
1407 :
1408 279 : locked = __mutex_trylock(lock);
1409 279 : if (locked)
1410 279 : mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1411 :
1412 279 : return locked;
1413 : }
1414 : EXPORT_SYMBOL(mutex_trylock);
1415 :
1416 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
1417 : int __sched
1418 : ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1419 : {
1420 : might_sleep();
1421 :
1422 : if (__mutex_trylock_fast(&lock->base)) {
1423 : if (ctx)
1424 : ww_mutex_set_context_fastpath(lock, ctx);
1425 : return 0;
1426 : }
1427 :
1428 : return __ww_mutex_lock_slowpath(lock, ctx);
1429 : }
1430 : EXPORT_SYMBOL(ww_mutex_lock);
1431 :
1432 : int __sched
1433 : ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1434 : {
1435 : might_sleep();
1436 :
1437 : if (__mutex_trylock_fast(&lock->base)) {
1438 : if (ctx)
1439 : ww_mutex_set_context_fastpath(lock, ctx);
1440 : return 0;
1441 : }
1442 :
1443 : return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1444 : }
1445 : EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1446 :
1447 : #endif
1448 :
1449 : /**
1450 : * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1451 : * @cnt: the atomic which we are to dec
1452 : * @lock: the mutex to return holding if we dec to 0
1453 : *
1454 : * return true and hold lock if we dec to 0, return false otherwise
1455 : */
1456 0 : int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1457 : {
1458 : /* dec if we can't possibly hit 0 */
1459 0 : if (atomic_add_unless(cnt, -1, 1))
1460 : return 0;
1461 : /* we might hit 0, so take the lock */
1462 0 : mutex_lock(lock);
1463 0 : if (!atomic_dec_and_test(cnt)) {
1464 : /* when we actually did the dec, we didn't hit 0 */
1465 0 : mutex_unlock(lock);
1466 0 : return 0;
1467 : }
1468 : /* we hit 0, and we hold the lock */
1469 : return 1;
1470 : }
1471 : EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
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