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 : #define CREATE_TRACE_POINTS
34 : #include <trace/events/lock.h>
35 :
36 : #ifndef CONFIG_PREEMPT_RT
37 : #include "mutex.h"
38 :
39 : #ifdef CONFIG_DEBUG_MUTEXES
40 : # define MUTEX_WARN_ON(cond) DEBUG_LOCKS_WARN_ON(cond)
41 : #else
42 : # define MUTEX_WARN_ON(cond)
43 : #endif
44 :
45 : void
46 1742 : __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
47 : {
48 3484 : atomic_long_set(&lock->owner, 0);
49 : raw_spin_lock_init(&lock->wait_lock);
50 3484 : INIT_LIST_HEAD(&lock->wait_list);
51 : #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
52 : osq_lock_init(&lock->osq);
53 : #endif
54 :
55 : debug_mutex_init(lock, name, key);
56 1742 : }
57 : EXPORT_SYMBOL(__mutex_init);
58 :
59 : /*
60 : * @owner: contains: 'struct task_struct *' to the current lock owner,
61 : * NULL means not owned. Since task_struct pointers are aligned at
62 : * at least L1_CACHE_BYTES, we have low bits to store extra state.
63 : *
64 : * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
65 : * Bit1 indicates unlock needs to hand the lock to the top-waiter
66 : * Bit2 indicates handoff has been done and we're waiting for pickup.
67 : */
68 : #define MUTEX_FLAG_WAITERS 0x01
69 : #define MUTEX_FLAG_HANDOFF 0x02
70 : #define MUTEX_FLAG_PICKUP 0x04
71 :
72 : #define MUTEX_FLAGS 0x07
73 :
74 : /*
75 : * Internal helper function; C doesn't allow us to hide it :/
76 : *
77 : * DO NOT USE (outside of mutex code).
78 : */
79 : static inline struct task_struct *__mutex_owner(struct mutex *lock)
80 : {
81 320 : return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
82 : }
83 :
84 : static inline struct task_struct *__owner_task(unsigned long owner)
85 : {
86 0 : return (struct task_struct *)(owner & ~MUTEX_FLAGS);
87 : }
88 :
89 160 : bool mutex_is_locked(struct mutex *lock)
90 : {
91 160 : return __mutex_owner(lock) != NULL;
92 : }
93 : EXPORT_SYMBOL(mutex_is_locked);
94 :
95 : static inline unsigned long __owner_flags(unsigned long owner)
96 : {
97 0 : return owner & MUTEX_FLAGS;
98 : }
99 :
100 : /*
101 : * Returns: __mutex_owner(lock) on failure or NULL on success.
102 : */
103 0 : static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff)
104 : {
105 0 : unsigned long owner, curr = (unsigned long)current;
106 :
107 0 : owner = atomic_long_read(&lock->owner);
108 : for (;;) { /* must loop, can race against a flag */
109 0 : unsigned long flags = __owner_flags(owner);
110 0 : unsigned long task = owner & ~MUTEX_FLAGS;
111 :
112 0 : if (task) {
113 0 : if (flags & MUTEX_FLAG_PICKUP) {
114 0 : if (task != curr)
115 : break;
116 0 : flags &= ~MUTEX_FLAG_PICKUP;
117 0 : } else if (handoff) {
118 0 : if (flags & MUTEX_FLAG_HANDOFF)
119 : break;
120 0 : flags |= MUTEX_FLAG_HANDOFF;
121 : } else {
122 : break;
123 : }
124 : } else {
125 : MUTEX_WARN_ON(flags & (MUTEX_FLAG_HANDOFF | MUTEX_FLAG_PICKUP));
126 : task = curr;
127 : }
128 :
129 0 : if (atomic_long_try_cmpxchg_acquire(&lock->owner, &owner, task | flags)) {
130 0 : if (task == curr)
131 : return NULL;
132 : break;
133 : }
134 : }
135 :
136 0 : return __owner_task(owner);
137 : }
138 :
139 : /*
140 : * Trylock or set HANDOFF
141 : */
142 : static inline bool __mutex_trylock_or_handoff(struct mutex *lock, bool handoff)
143 : {
144 0 : return !__mutex_trylock_common(lock, handoff);
145 : }
146 :
147 : /*
148 : * Actual trylock that will work on any unlocked state.
149 : */
150 : static inline bool __mutex_trylock(struct mutex *lock)
151 : {
152 0 : return !__mutex_trylock_common(lock, false);
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 : */
166 : static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
167 : {
168 5382 : unsigned long curr = (unsigned long)current;
169 5382 : unsigned long zero = 0UL;
170 :
171 10764 : if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
172 : return true;
173 :
174 : return false;
175 : }
176 :
177 : static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
178 : {
179 5377 : unsigned long curr = (unsigned long)current;
180 :
181 10754 : return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
182 : }
183 : #endif
184 :
185 : static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
186 : {
187 0 : atomic_long_or(flag, &lock->owner);
188 : }
189 :
190 : static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
191 : {
192 0 : atomic_long_andnot(flag, &lock->owner);
193 : }
194 :
195 : static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
196 : {
197 0 : return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
198 : }
199 :
200 : /*
201 : * Add @waiter to a given location in the lock wait_list and set the
202 : * FLAG_WAITERS flag if it's the first waiter.
203 : */
204 : static void
205 : __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
206 : struct list_head *list)
207 : {
208 : debug_mutex_add_waiter(lock, waiter, current);
209 :
210 0 : list_add_tail(&waiter->list, list);
211 0 : if (__mutex_waiter_is_first(lock, waiter))
212 : __mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
213 : }
214 :
215 : static void
216 0 : __mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter)
217 : {
218 0 : list_del(&waiter->list);
219 0 : if (likely(list_empty(&lock->wait_list)))
220 : __mutex_clear_flag(lock, MUTEX_FLAGS);
221 :
222 : debug_mutex_remove_waiter(lock, waiter, current);
223 0 : }
224 :
225 : /*
226 : * Give up ownership to a specific task, when @task = NULL, this is equivalent
227 : * to a regular unlock. Sets PICKUP on a handoff, clears HANDOFF, preserves
228 : * WAITERS. Provides RELEASE semantics like a regular unlock, the
229 : * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
230 : */
231 : static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
232 : {
233 0 : unsigned long owner = atomic_long_read(&lock->owner);
234 :
235 : for (;;) {
236 : unsigned long new;
237 :
238 : MUTEX_WARN_ON(__owner_task(owner) != current);
239 : MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
240 :
241 0 : new = (owner & MUTEX_FLAG_WAITERS);
242 0 : new |= (unsigned long)task;
243 0 : if (task)
244 0 : new |= MUTEX_FLAG_PICKUP;
245 :
246 0 : if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, new))
247 : break;
248 : }
249 : }
250 :
251 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
252 : /*
253 : * We split the mutex lock/unlock logic into separate fastpath and
254 : * slowpath functions, to reduce the register pressure on the fastpath.
255 : * We also put the fastpath first in the kernel image, to make sure the
256 : * branch is predicted by the CPU as default-untaken.
257 : */
258 : static void __sched __mutex_lock_slowpath(struct mutex *lock);
259 :
260 : /**
261 : * mutex_lock - acquire the mutex
262 : * @lock: the mutex to be acquired
263 : *
264 : * Lock the mutex exclusively for this task. If the mutex is not
265 : * available right now, it will sleep until it can get it.
266 : *
267 : * The mutex must later on be released by the same task that
268 : * acquired it. Recursive locking is not allowed. The task
269 : * may not exit without first unlocking the mutex. Also, kernel
270 : * memory where the mutex resides must not be freed with
271 : * the mutex still locked. The mutex must first be initialized
272 : * (or statically defined) before it can be locked. memset()-ing
273 : * the mutex to 0 is not allowed.
274 : *
275 : * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
276 : * checks that will enforce the restrictions and will also do
277 : * deadlock debugging)
278 : *
279 : * This function is similar to (but not equivalent to) down().
280 : */
281 5095 : void __sched mutex_lock(struct mutex *lock)
282 : {
283 : might_sleep();
284 :
285 5095 : if (!__mutex_trylock_fast(lock))
286 0 : __mutex_lock_slowpath(lock);
287 5095 : }
288 : EXPORT_SYMBOL(mutex_lock);
289 : #endif
290 :
291 : #include "ww_mutex.h"
292 :
293 : #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
294 :
295 : /*
296 : * Trylock variant that returns the owning task on failure.
297 : */
298 : static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
299 : {
300 : return __mutex_trylock_common(lock, false);
301 : }
302 :
303 : static inline
304 : bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
305 : struct mutex_waiter *waiter)
306 : {
307 : struct ww_mutex *ww;
308 :
309 : ww = container_of(lock, struct ww_mutex, base);
310 :
311 : /*
312 : * If ww->ctx is set the contents are undefined, only
313 : * by acquiring wait_lock there is a guarantee that
314 : * they are not invalid when reading.
315 : *
316 : * As such, when deadlock detection needs to be
317 : * performed the optimistic spinning cannot be done.
318 : *
319 : * Check this in every inner iteration because we may
320 : * be racing against another thread's ww_mutex_lock.
321 : */
322 : if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
323 : return false;
324 :
325 : /*
326 : * If we aren't on the wait list yet, cancel the spin
327 : * if there are waiters. We want to avoid stealing the
328 : * lock from a waiter with an earlier stamp, since the
329 : * other thread may already own a lock that we also
330 : * need.
331 : */
332 : if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
333 : return false;
334 :
335 : /*
336 : * Similarly, stop spinning if we are no longer the
337 : * first waiter.
338 : */
339 : if (waiter && !__mutex_waiter_is_first(lock, waiter))
340 : return false;
341 :
342 : return true;
343 : }
344 :
345 : /*
346 : * Look out! "owner" is an entirely speculative pointer access and not
347 : * reliable.
348 : *
349 : * "noinline" so that this function shows up on perf profiles.
350 : */
351 : static noinline
352 : bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
353 : struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
354 : {
355 : bool ret = true;
356 :
357 : lockdep_assert_preemption_disabled();
358 :
359 : while (__mutex_owner(lock) == owner) {
360 : /*
361 : * Ensure we emit the owner->on_cpu, dereference _after_
362 : * checking lock->owner still matches owner. And we already
363 : * disabled preemption which is equal to the RCU read-side
364 : * crital section in optimistic spinning code. Thus the
365 : * task_strcut structure won't go away during the spinning
366 : * period
367 : */
368 : barrier();
369 :
370 : /*
371 : * Use vcpu_is_preempted to detect lock holder preemption issue.
372 : */
373 : if (!owner_on_cpu(owner) || need_resched()) {
374 : ret = false;
375 : break;
376 : }
377 :
378 : if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
379 : ret = false;
380 : break;
381 : }
382 :
383 : cpu_relax();
384 : }
385 :
386 : return ret;
387 : }
388 :
389 : /*
390 : * Initial check for entering the mutex spinning loop
391 : */
392 : static inline int mutex_can_spin_on_owner(struct mutex *lock)
393 : {
394 : struct task_struct *owner;
395 : int retval = 1;
396 :
397 : lockdep_assert_preemption_disabled();
398 :
399 : if (need_resched())
400 : return 0;
401 :
402 : /*
403 : * We already disabled preemption which is equal to the RCU read-side
404 : * crital section in optimistic spinning code. Thus the task_strcut
405 : * structure won't go away during the spinning period.
406 : */
407 : owner = __mutex_owner(lock);
408 : if (owner)
409 : retval = owner_on_cpu(owner);
410 :
411 : /*
412 : * If lock->owner is not set, the mutex has been released. Return true
413 : * such that we'll trylock in the spin path, which is a faster option
414 : * than the blocking slow path.
415 : */
416 : return retval;
417 : }
418 :
419 : /*
420 : * Optimistic spinning.
421 : *
422 : * We try to spin for acquisition when we find that the lock owner
423 : * is currently running on a (different) CPU and while we don't
424 : * need to reschedule. The rationale is that if the lock owner is
425 : * running, it is likely to release the lock soon.
426 : *
427 : * The mutex spinners are queued up using MCS lock so that only one
428 : * spinner can compete for the mutex. However, if mutex spinning isn't
429 : * going to happen, there is no point in going through the lock/unlock
430 : * overhead.
431 : *
432 : * Returns true when the lock was taken, otherwise false, indicating
433 : * that we need to jump to the slowpath and sleep.
434 : *
435 : * The waiter flag is set to true if the spinner is a waiter in the wait
436 : * queue. The waiter-spinner will spin on the lock directly and concurrently
437 : * with the spinner at the head of the OSQ, if present, until the owner is
438 : * changed to itself.
439 : */
440 : static __always_inline bool
441 : mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
442 : struct mutex_waiter *waiter)
443 : {
444 : if (!waiter) {
445 : /*
446 : * The purpose of the mutex_can_spin_on_owner() function is
447 : * to eliminate the overhead of osq_lock() and osq_unlock()
448 : * in case spinning isn't possible. As a waiter-spinner
449 : * is not going to take OSQ lock anyway, there is no need
450 : * to call mutex_can_spin_on_owner().
451 : */
452 : if (!mutex_can_spin_on_owner(lock))
453 : goto fail;
454 :
455 : /*
456 : * In order to avoid a stampede of mutex spinners trying to
457 : * acquire the mutex all at once, the spinners need to take a
458 : * MCS (queued) lock first before spinning on the owner field.
459 : */
460 : if (!osq_lock(&lock->osq))
461 : goto fail;
462 : }
463 :
464 : for (;;) {
465 : struct task_struct *owner;
466 :
467 : /* Try to acquire the mutex... */
468 : owner = __mutex_trylock_or_owner(lock);
469 : if (!owner)
470 : break;
471 :
472 : /*
473 : * There's an owner, wait for it to either
474 : * release the lock or go to sleep.
475 : */
476 : if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
477 : goto fail_unlock;
478 :
479 : /*
480 : * The cpu_relax() call is a compiler barrier which forces
481 : * everything in this loop to be re-loaded. We don't need
482 : * memory barriers as we'll eventually observe the right
483 : * values at the cost of a few extra spins.
484 : */
485 : cpu_relax();
486 : }
487 :
488 : if (!waiter)
489 : osq_unlock(&lock->osq);
490 :
491 : return true;
492 :
493 :
494 : fail_unlock:
495 : if (!waiter)
496 : osq_unlock(&lock->osq);
497 :
498 : fail:
499 : /*
500 : * If we fell out of the spin path because of need_resched(),
501 : * reschedule now, before we try-lock the mutex. This avoids getting
502 : * scheduled out right after we obtained the mutex.
503 : */
504 : if (need_resched()) {
505 : /*
506 : * We _should_ have TASK_RUNNING here, but just in case
507 : * we do not, make it so, otherwise we might get stuck.
508 : */
509 : __set_current_state(TASK_RUNNING);
510 : schedule_preempt_disabled();
511 : }
512 :
513 : return false;
514 : }
515 : #else
516 : static __always_inline bool
517 : mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
518 : struct mutex_waiter *waiter)
519 : {
520 : return false;
521 : }
522 : #endif
523 :
524 : static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
525 :
526 : /**
527 : * mutex_unlock - release the mutex
528 : * @lock: the mutex to be released
529 : *
530 : * Unlock a mutex that has been locked by this task previously.
531 : *
532 : * This function must not be used in interrupt context. Unlocking
533 : * of a not locked mutex is not allowed.
534 : *
535 : * This function is similar to (but not equivalent to) up().
536 : */
537 5372 : void __sched mutex_unlock(struct mutex *lock)
538 : {
539 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
540 5377 : if (__mutex_unlock_fast(lock))
541 : return;
542 : #endif
543 0 : __mutex_unlock_slowpath(lock, _RET_IP_);
544 : }
545 : EXPORT_SYMBOL(mutex_unlock);
546 :
547 : /**
548 : * ww_mutex_unlock - release the w/w mutex
549 : * @lock: the mutex to be released
550 : *
551 : * Unlock a mutex that has been locked by this task previously with any of the
552 : * ww_mutex_lock* functions (with or without an acquire context). It is
553 : * forbidden to release the locks after releasing the acquire context.
554 : *
555 : * This function must not be used in interrupt context. Unlocking
556 : * of a unlocked mutex is not allowed.
557 : */
558 5 : void __sched ww_mutex_unlock(struct ww_mutex *lock)
559 : {
560 5 : __ww_mutex_unlock(lock);
561 10 : mutex_unlock(&lock->base);
562 5 : }
563 : EXPORT_SYMBOL(ww_mutex_unlock);
564 :
565 : /*
566 : * Lock a mutex (possibly interruptible), slowpath:
567 : */
568 : static __always_inline int __sched
569 : __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclass,
570 : struct lockdep_map *nest_lock, unsigned long ip,
571 : struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
572 : {
573 : struct mutex_waiter waiter;
574 : struct ww_mutex *ww;
575 : int ret;
576 :
577 : if (!use_ww_ctx)
578 0 : ww_ctx = NULL;
579 :
580 : might_sleep();
581 :
582 : MUTEX_WARN_ON(lock->magic != lock);
583 :
584 5 : ww = container_of(lock, struct ww_mutex, base);
585 5 : if (ww_ctx) {
586 5 : if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
587 : return -EALREADY;
588 :
589 : /*
590 : * Reset the wounded flag after a kill. No other process can
591 : * race and wound us here since they can't have a valid owner
592 : * pointer if we don't have any locks held.
593 : */
594 0 : if (ww_ctx->acquired == 0)
595 0 : ww_ctx->wounded = 0;
596 :
597 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
598 : nest_lock = &ww_ctx->dep_map;
599 : #endif
600 : }
601 :
602 0 : preempt_disable();
603 : mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
604 :
605 0 : trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);
606 0 : if (__mutex_trylock(lock) ||
607 0 : mutex_optimistic_spin(lock, ww_ctx, NULL)) {
608 : /* got the lock, yay! */
609 : lock_acquired(&lock->dep_map, ip);
610 0 : if (ww_ctx)
611 : ww_mutex_set_context_fastpath(ww, ww_ctx);
612 0 : trace_contention_end(lock, 0);
613 0 : preempt_enable();
614 : return 0;
615 : }
616 :
617 0 : raw_spin_lock(&lock->wait_lock);
618 : /*
619 : * After waiting to acquire the wait_lock, try again.
620 : */
621 0 : if (__mutex_trylock(lock)) {
622 0 : if (ww_ctx)
623 0 : __ww_mutex_check_waiters(lock, ww_ctx);
624 :
625 : goto skip_wait;
626 : }
627 :
628 : debug_mutex_lock_common(lock, &waiter);
629 0 : waiter.task = current;
630 : if (use_ww_ctx)
631 0 : waiter.ww_ctx = ww_ctx;
632 :
633 : lock_contended(&lock->dep_map, ip);
634 :
635 : if (!use_ww_ctx) {
636 : /* add waiting tasks to the end of the waitqueue (FIFO): */
637 0 : __mutex_add_waiter(lock, &waiter, &lock->wait_list);
638 : } else {
639 : /*
640 : * Add in stamp order, waking up waiters that must kill
641 : * themselves.
642 : */
643 0 : ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
644 0 : if (ret)
645 : goto err_early_kill;
646 : }
647 :
648 0 : set_current_state(state);
649 0 : trace_contention_begin(lock, LCB_F_MUTEX);
650 : for (;;) {
651 : bool first;
652 :
653 : /*
654 : * Once we hold wait_lock, we're serialized against
655 : * mutex_unlock() handing the lock off to us, do a trylock
656 : * before testing the error conditions to make sure we pick up
657 : * the handoff.
658 : */
659 0 : if (__mutex_trylock(lock))
660 : goto acquired;
661 :
662 : /*
663 : * Check for signals and kill conditions while holding
664 : * wait_lock. This ensures the lock cancellation is ordered
665 : * against mutex_unlock() and wake-ups do not go missing.
666 : */
667 0 : if (signal_pending_state(state, current)) {
668 : ret = -EINTR;
669 : goto err;
670 : }
671 :
672 0 : if (ww_ctx) {
673 0 : ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
674 0 : if (ret)
675 : goto err;
676 : }
677 :
678 0 : raw_spin_unlock(&lock->wait_lock);
679 0 : schedule_preempt_disabled();
680 :
681 0 : first = __mutex_waiter_is_first(lock, &waiter);
682 :
683 0 : set_current_state(state);
684 : /*
685 : * Here we order against unlock; we must either see it change
686 : * state back to RUNNING and fall through the next schedule(),
687 : * or we must see its unlock and acquire.
688 : */
689 0 : if (__mutex_trylock_or_handoff(lock, first))
690 : break;
691 :
692 : if (first) {
693 : trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN);
694 : if (mutex_optimistic_spin(lock, ww_ctx, &waiter))
695 : break;
696 : trace_contention_begin(lock, LCB_F_MUTEX);
697 : }
698 :
699 0 : raw_spin_lock(&lock->wait_lock);
700 : }
701 0 : raw_spin_lock(&lock->wait_lock);
702 : acquired:
703 0 : __set_current_state(TASK_RUNNING);
704 :
705 0 : if (ww_ctx) {
706 : /*
707 : * Wound-Wait; we stole the lock (!first_waiter), check the
708 : * waiters as anyone might want to wound us.
709 : */
710 0 : if (!ww_ctx->is_wait_die &&
711 0 : !__mutex_waiter_is_first(lock, &waiter))
712 0 : __ww_mutex_check_waiters(lock, ww_ctx);
713 : }
714 :
715 0 : __mutex_remove_waiter(lock, &waiter);
716 :
717 : debug_mutex_free_waiter(&waiter);
718 :
719 : skip_wait:
720 : /* got the lock - cleanup and rejoice! */
721 : lock_acquired(&lock->dep_map, ip);
722 0 : trace_contention_end(lock, 0);
723 :
724 0 : if (ww_ctx)
725 : ww_mutex_lock_acquired(ww, ww_ctx);
726 :
727 0 : raw_spin_unlock(&lock->wait_lock);
728 0 : preempt_enable();
729 : return 0;
730 :
731 : err:
732 0 : __set_current_state(TASK_RUNNING);
733 0 : __mutex_remove_waiter(lock, &waiter);
734 : err_early_kill:
735 0 : trace_contention_end(lock, ret);
736 0 : raw_spin_unlock(&lock->wait_lock);
737 : debug_mutex_free_waiter(&waiter);
738 : mutex_release(&lock->dep_map, ip);
739 0 : preempt_enable();
740 : return ret;
741 : }
742 :
743 : static int __sched
744 0 : __mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
745 : struct lockdep_map *nest_lock, unsigned long ip)
746 : {
747 0 : return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
748 : }
749 :
750 : static int __sched
751 5 : __ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
752 : unsigned long ip, struct ww_acquire_ctx *ww_ctx)
753 : {
754 5 : return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
755 : }
756 :
757 : /**
758 : * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
759 : * @ww: mutex to lock
760 : * @ww_ctx: optional w/w acquire context
761 : *
762 : * Trylocks a mutex with the optional acquire context; no deadlock detection is
763 : * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
764 : *
765 : * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
766 : * specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
767 : *
768 : * A mutex acquired with this function must be released with ww_mutex_unlock.
769 : */
770 0 : int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
771 : {
772 0 : if (!ww_ctx)
773 0 : return mutex_trylock(&ww->base);
774 :
775 : MUTEX_WARN_ON(ww->base.magic != &ww->base);
776 :
777 : /*
778 : * Reset the wounded flag after a kill. No other process can
779 : * race and wound us here, since they can't have a valid owner
780 : * pointer if we don't have any locks held.
781 : */
782 0 : if (ww_ctx->acquired == 0)
783 0 : ww_ctx->wounded = 0;
784 :
785 0 : if (__mutex_trylock(&ww->base)) {
786 : ww_mutex_set_context_fastpath(ww, ww_ctx);
787 : mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
788 : return 1;
789 : }
790 :
791 : return 0;
792 : }
793 : EXPORT_SYMBOL(ww_mutex_trylock);
794 :
795 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
796 : void __sched
797 : mutex_lock_nested(struct mutex *lock, unsigned int subclass)
798 : {
799 : __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
800 : }
801 :
802 : EXPORT_SYMBOL_GPL(mutex_lock_nested);
803 :
804 : void __sched
805 : _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
806 : {
807 : __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
808 : }
809 : EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
810 :
811 : int __sched
812 : mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
813 : {
814 : return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
815 : }
816 : EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
817 :
818 : int __sched
819 : mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
820 : {
821 : return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
822 : }
823 : EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
824 :
825 : void __sched
826 : mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
827 : {
828 : int token;
829 :
830 : might_sleep();
831 :
832 : token = io_schedule_prepare();
833 : __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
834 : subclass, NULL, _RET_IP_, NULL, 0);
835 : io_schedule_finish(token);
836 : }
837 : EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
838 :
839 : static inline int
840 : ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
841 : {
842 : #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
843 : unsigned tmp;
844 :
845 : if (ctx->deadlock_inject_countdown-- == 0) {
846 : tmp = ctx->deadlock_inject_interval;
847 : if (tmp > UINT_MAX/4)
848 : tmp = UINT_MAX;
849 : else
850 : tmp = tmp*2 + tmp + tmp/2;
851 :
852 : ctx->deadlock_inject_interval = tmp;
853 : ctx->deadlock_inject_countdown = tmp;
854 : ctx->contending_lock = lock;
855 :
856 : ww_mutex_unlock(lock);
857 :
858 : return -EDEADLK;
859 : }
860 : #endif
861 :
862 : return 0;
863 : }
864 :
865 : int __sched
866 : ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
867 : {
868 : int ret;
869 :
870 : might_sleep();
871 : ret = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
872 : 0, _RET_IP_, ctx);
873 : if (!ret && ctx && ctx->acquired > 1)
874 : return ww_mutex_deadlock_injection(lock, ctx);
875 :
876 : return ret;
877 : }
878 : EXPORT_SYMBOL_GPL(ww_mutex_lock);
879 :
880 : int __sched
881 : ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
882 : {
883 : int ret;
884 :
885 : might_sleep();
886 : ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
887 : 0, _RET_IP_, ctx);
888 :
889 : if (!ret && ctx && ctx->acquired > 1)
890 : return ww_mutex_deadlock_injection(lock, ctx);
891 :
892 : return ret;
893 : }
894 : EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
895 :
896 : #endif
897 :
898 : /*
899 : * Release the lock, slowpath:
900 : */
901 0 : static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
902 : {
903 0 : struct task_struct *next = NULL;
904 0 : DEFINE_WAKE_Q(wake_q);
905 : unsigned long owner;
906 :
907 : mutex_release(&lock->dep_map, ip);
908 :
909 : /*
910 : * Release the lock before (potentially) taking the spinlock such that
911 : * other contenders can get on with things ASAP.
912 : *
913 : * Except when HANDOFF, in that case we must not clear the owner field,
914 : * but instead set it to the top waiter.
915 : */
916 0 : owner = atomic_long_read(&lock->owner);
917 : for (;;) {
918 : MUTEX_WARN_ON(__owner_task(owner) != current);
919 : MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
920 :
921 0 : if (owner & MUTEX_FLAG_HANDOFF)
922 : break;
923 :
924 0 : if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
925 0 : if (owner & MUTEX_FLAG_WAITERS)
926 : break;
927 :
928 0 : return;
929 : }
930 : }
931 :
932 0 : raw_spin_lock(&lock->wait_lock);
933 : debug_mutex_unlock(lock);
934 0 : if (!list_empty(&lock->wait_list)) {
935 : /* get the first entry from the wait-list: */
936 0 : struct mutex_waiter *waiter =
937 0 : list_first_entry(&lock->wait_list,
938 : struct mutex_waiter, list);
939 :
940 0 : next = waiter->task;
941 :
942 : debug_mutex_wake_waiter(lock, waiter);
943 0 : wake_q_add(&wake_q, next);
944 : }
945 :
946 0 : if (owner & MUTEX_FLAG_HANDOFF)
947 : __mutex_handoff(lock, next);
948 :
949 0 : raw_spin_unlock(&lock->wait_lock);
950 :
951 0 : wake_up_q(&wake_q);
952 : }
953 :
954 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
955 : /*
956 : * Here come the less common (and hence less performance-critical) APIs:
957 : * mutex_lock_interruptible() and mutex_trylock().
958 : */
959 : static noinline int __sched
960 : __mutex_lock_killable_slowpath(struct mutex *lock);
961 :
962 : static noinline int __sched
963 : __mutex_lock_interruptible_slowpath(struct mutex *lock);
964 :
965 : /**
966 : * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
967 : * @lock: The mutex to be acquired.
968 : *
969 : * Lock the mutex like mutex_lock(). If a signal is delivered while the
970 : * process is sleeping, this function will return without acquiring the
971 : * mutex.
972 : *
973 : * Context: Process context.
974 : * Return: 0 if the lock was successfully acquired or %-EINTR if a
975 : * signal arrived.
976 : */
977 0 : int __sched mutex_lock_interruptible(struct mutex *lock)
978 : {
979 : might_sleep();
980 :
981 0 : if (__mutex_trylock_fast(lock))
982 : return 0;
983 :
984 0 : return __mutex_lock_interruptible_slowpath(lock);
985 : }
986 :
987 : EXPORT_SYMBOL(mutex_lock_interruptible);
988 :
989 : /**
990 : * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
991 : * @lock: The mutex to be acquired.
992 : *
993 : * Lock the mutex like mutex_lock(). If a signal which will be fatal to
994 : * the current process is delivered while the process is sleeping, this
995 : * function will return without acquiring the mutex.
996 : *
997 : * Context: Process context.
998 : * Return: 0 if the lock was successfully acquired or %-EINTR if a
999 : * fatal signal arrived.
1000 : */
1001 277 : int __sched mutex_lock_killable(struct mutex *lock)
1002 : {
1003 : might_sleep();
1004 :
1005 277 : if (__mutex_trylock_fast(lock))
1006 : return 0;
1007 :
1008 0 : return __mutex_lock_killable_slowpath(lock);
1009 : }
1010 : EXPORT_SYMBOL(mutex_lock_killable);
1011 :
1012 : /**
1013 : * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1014 : * @lock: The mutex to be acquired.
1015 : *
1016 : * Lock the mutex like mutex_lock(). While the task is waiting for this
1017 : * mutex, it will be accounted as being in the IO wait state by the
1018 : * scheduler.
1019 : *
1020 : * Context: Process context.
1021 : */
1022 0 : void __sched mutex_lock_io(struct mutex *lock)
1023 : {
1024 : int token;
1025 :
1026 0 : token = io_schedule_prepare();
1027 0 : mutex_lock(lock);
1028 0 : io_schedule_finish(token);
1029 0 : }
1030 : EXPORT_SYMBOL_GPL(mutex_lock_io);
1031 :
1032 : static noinline void __sched
1033 0 : __mutex_lock_slowpath(struct mutex *lock)
1034 : {
1035 0 : __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1036 0 : }
1037 :
1038 : static noinline int __sched
1039 0 : __mutex_lock_killable_slowpath(struct mutex *lock)
1040 : {
1041 0 : return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1042 : }
1043 :
1044 : static noinline int __sched
1045 0 : __mutex_lock_interruptible_slowpath(struct mutex *lock)
1046 : {
1047 0 : return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1048 : }
1049 :
1050 : static noinline int __sched
1051 5 : __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1052 : {
1053 5 : return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0,
1054 5 : _RET_IP_, ctx);
1055 : }
1056 :
1057 : static noinline int __sched
1058 0 : __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1059 : struct ww_acquire_ctx *ctx)
1060 : {
1061 0 : return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0,
1062 0 : _RET_IP_, ctx);
1063 : }
1064 :
1065 : #endif
1066 :
1067 : /**
1068 : * mutex_trylock - try to acquire the mutex, without waiting
1069 : * @lock: the mutex to be acquired
1070 : *
1071 : * Try to acquire the mutex atomically. Returns 1 if the mutex
1072 : * has been acquired successfully, and 0 on contention.
1073 : *
1074 : * NOTE: this function follows the spin_trylock() convention, so
1075 : * it is negated from the down_trylock() return values! Be careful
1076 : * about this when converting semaphore users to mutexes.
1077 : *
1078 : * This function must not be used in interrupt context. The
1079 : * mutex must be released by the same task that acquired it.
1080 : */
1081 0 : int __sched mutex_trylock(struct mutex *lock)
1082 : {
1083 : bool locked;
1084 :
1085 : MUTEX_WARN_ON(lock->magic != lock);
1086 :
1087 0 : locked = __mutex_trylock(lock);
1088 : if (locked)
1089 : mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1090 :
1091 0 : return locked;
1092 : }
1093 : EXPORT_SYMBOL(mutex_trylock);
1094 :
1095 : #ifndef CONFIG_DEBUG_LOCK_ALLOC
1096 : int __sched
1097 10 : ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1098 : {
1099 : might_sleep();
1100 :
1101 20 : if (__mutex_trylock_fast(&lock->base)) {
1102 5 : if (ctx)
1103 : ww_mutex_set_context_fastpath(lock, ctx);
1104 : return 0;
1105 : }
1106 :
1107 5 : return __ww_mutex_lock_slowpath(lock, ctx);
1108 : }
1109 : EXPORT_SYMBOL(ww_mutex_lock);
1110 :
1111 : int __sched
1112 0 : ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1113 : {
1114 : might_sleep();
1115 :
1116 0 : if (__mutex_trylock_fast(&lock->base)) {
1117 0 : if (ctx)
1118 : ww_mutex_set_context_fastpath(lock, ctx);
1119 : return 0;
1120 : }
1121 :
1122 0 : return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1123 : }
1124 : EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1125 :
1126 : #endif /* !CONFIG_DEBUG_LOCK_ALLOC */
1127 : #endif /* !CONFIG_PREEMPT_RT */
1128 :
1129 : /**
1130 : * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1131 : * @cnt: the atomic which we are to dec
1132 : * @lock: the mutex to return holding if we dec to 0
1133 : *
1134 : * return true and hold lock if we dec to 0, return false otherwise
1135 : */
1136 0 : int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1137 : {
1138 : /* dec if we can't possibly hit 0 */
1139 0 : if (atomic_add_unless(cnt, -1, 1))
1140 : return 0;
1141 : /* we might hit 0, so take the lock */
1142 0 : mutex_lock(lock);
1143 0 : if (!atomic_dec_and_test(cnt)) {
1144 : /* when we actually did the dec, we didn't hit 0 */
1145 : mutex_unlock(lock);
1146 : return 0;
1147 : }
1148 : /* we hit 0, and we hold the lock */
1149 : return 1;
1150 : }
1151 : EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
|
