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Linux/kernel/locking/mutex.c

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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.h>
 23 #include <linux/sched/rt.h>
 24 #include <linux/export.h>
 25 #include <linux/spinlock.h>
 26 #include <linux/interrupt.h>
 27 #include <linux/debug_locks.h>
 28 #include <linux/osq_lock.h>
 29 
 30 /*
 31  * In the DEBUG case we are using the "NULL fastpath" for mutexes,
 32  * which forces all calls into the slowpath:
 33  */
 34 #ifdef CONFIG_DEBUG_MUTEXES
 35 # include "mutex-debug.h"
 36 # include <asm-generic/mutex-null.h>
 37 /*
 38  * Must be 0 for the debug case so we do not do the unlock outside of the
 39  * wait_lock region. debug_mutex_unlock() will do the actual unlock in this
 40  * case.
 41  */
 42 # undef __mutex_slowpath_needs_to_unlock
 43 # define  __mutex_slowpath_needs_to_unlock()    0
 44 #else
 45 # include "mutex.h"
 46 # include <asm/mutex.h>
 47 #endif
 48 
 49 void
 50 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 51 {
 52         atomic_set(&lock->count, 1);
 53         spin_lock_init(&lock->wait_lock);
 54         INIT_LIST_HEAD(&lock->wait_list);
 55         mutex_clear_owner(lock);
 56 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 57         osq_lock_init(&lock->osq);
 58 #endif
 59 
 60         debug_mutex_init(lock, name, key);
 61 }
 62 
 63 EXPORT_SYMBOL(__mutex_init);
 64 
 65 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 66 /*
 67  * We split the mutex lock/unlock logic into separate fastpath and
 68  * slowpath functions, to reduce the register pressure on the fastpath.
 69  * We also put the fastpath first in the kernel image, to make sure the
 70  * branch is predicted by the CPU as default-untaken.
 71  */
 72 __visible void __sched __mutex_lock_slowpath(atomic_t *lock_count);
 73 
 74 /**
 75  * mutex_lock - acquire the mutex
 76  * @lock: the mutex to be acquired
 77  *
 78  * Lock the mutex exclusively for this task. If the mutex is not
 79  * available right now, it will sleep until it can get it.
 80  *
 81  * The mutex must later on be released by the same task that
 82  * acquired it. Recursive locking is not allowed. The task
 83  * may not exit without first unlocking the mutex. Also, kernel
 84  * memory where the mutex resides must not be freed with
 85  * the mutex still locked. The mutex must first be initialized
 86  * (or statically defined) before it can be locked. memset()-ing
 87  * the mutex to 0 is not allowed.
 88  *
 89  * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
 90  *   checks that will enforce the restrictions and will also do
 91  *   deadlock debugging. )
 92  *
 93  * This function is similar to (but not equivalent to) down().
 94  */
 95 void __sched mutex_lock(struct mutex *lock)
 96 {
 97         might_sleep();
 98         /*
 99          * The locking fastpath is the 1->0 transition from
100          * 'unlocked' into 'locked' state.
101          */
102         __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
103         mutex_set_owner(lock);
104 }
105 
106 EXPORT_SYMBOL(mutex_lock);
107 #endif
108 
109 static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
110                                                    struct ww_acquire_ctx *ww_ctx)
111 {
112 #ifdef CONFIG_DEBUG_MUTEXES
113         /*
114          * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
115          * but released with a normal mutex_unlock in this call.
116          *
117          * This should never happen, always use ww_mutex_unlock.
118          */
119         DEBUG_LOCKS_WARN_ON(ww->ctx);
120 
121         /*
122          * Not quite done after calling ww_acquire_done() ?
123          */
124         DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
125 
126         if (ww_ctx->contending_lock) {
127                 /*
128                  * After -EDEADLK you tried to
129                  * acquire a different ww_mutex? Bad!
130                  */
131                 DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
132 
133                 /*
134                  * You called ww_mutex_lock after receiving -EDEADLK,
135                  * but 'forgot' to unlock everything else first?
136                  */
137                 DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
138                 ww_ctx->contending_lock = NULL;
139         }
140 
141         /*
142          * Naughty, using a different class will lead to undefined behavior!
143          */
144         DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
145 #endif
146         ww_ctx->acquired++;
147 }
148 
149 /*
150  * After acquiring lock with fastpath or when we lost out in contested
151  * slowpath, set ctx and wake up any waiters so they can recheck.
152  *
153  * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
154  * as the fastpath and opportunistic spinning are disabled in that case.
155  */
156 static __always_inline void
157 ww_mutex_set_context_fastpath(struct ww_mutex *lock,
158                                struct ww_acquire_ctx *ctx)
159 {
160         unsigned long flags;
161         struct mutex_waiter *cur;
162 
163         ww_mutex_lock_acquired(lock, ctx);
164 
165         lock->ctx = ctx;
166 
167         /*
168          * The lock->ctx update should be visible on all cores before
169          * the atomic read is done, otherwise contended waiters might be
170          * missed. The contended waiters will either see ww_ctx == NULL
171          * and keep spinning, or it will acquire wait_lock, add itself
172          * to waiter list and sleep.
173          */
174         smp_mb(); /* ^^^ */
175 
176         /*
177          * Check if lock is contended, if not there is nobody to wake up
178          */
179         if (likely(atomic_read(&lock->base.count) == 0))
180                 return;
181 
182         /*
183          * Uh oh, we raced in fastpath, wake up everyone in this case,
184          * so they can see the new lock->ctx.
185          */
186         spin_lock_mutex(&lock->base.wait_lock, flags);
187         list_for_each_entry(cur, &lock->base.wait_list, list) {
188                 debug_mutex_wake_waiter(&lock->base, cur);
189                 wake_up_process(cur->task);
190         }
191         spin_unlock_mutex(&lock->base.wait_lock, flags);
192 }
193 
194 /*
195  * After acquiring lock in the slowpath set ctx and wake up any
196  * waiters so they can recheck.
197  *
198  * Callers must hold the mutex wait_lock.
199  */
200 static __always_inline void
201 ww_mutex_set_context_slowpath(struct ww_mutex *lock,
202                               struct ww_acquire_ctx *ctx)
203 {
204         struct mutex_waiter *cur;
205 
206         ww_mutex_lock_acquired(lock, ctx);
207         lock->ctx = ctx;
208 
209         /*
210          * Give any possible sleeping processes the chance to wake up,
211          * so they can recheck if they have to back off.
212          */
213         list_for_each_entry(cur, &lock->base.wait_list, list) {
214                 debug_mutex_wake_waiter(&lock->base, cur);
215                 wake_up_process(cur->task);
216         }
217 }
218 
219 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
220 /*
221  * Look out! "owner" is an entirely speculative pointer
222  * access and not reliable.
223  */
224 static noinline
225 bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
226 {
227         bool ret = true;
228 
229         rcu_read_lock();
230         while (lock->owner == owner) {
231                 /*
232                  * Ensure we emit the owner->on_cpu, dereference _after_
233                  * checking lock->owner still matches owner. If that fails,
234                  * owner might point to freed memory. If it still matches,
235                  * the rcu_read_lock() ensures the memory stays valid.
236                  */
237                 barrier();
238 
239                 if (!owner->on_cpu || need_resched()) {
240                         ret = false;
241                         break;
242                 }
243 
244                 cpu_relax_lowlatency();
245         }
246         rcu_read_unlock();
247 
248         return ret;
249 }
250 
251 /*
252  * Initial check for entering the mutex spinning loop
253  */
254 static inline int mutex_can_spin_on_owner(struct mutex *lock)
255 {
256         struct task_struct *owner;
257         int retval = 1;
258 
259         if (need_resched())
260                 return 0;
261 
262         rcu_read_lock();
263         owner = READ_ONCE(lock->owner);
264         if (owner)
265                 retval = owner->on_cpu;
266         rcu_read_unlock();
267         /*
268          * if lock->owner is not set, the mutex owner may have just acquired
269          * it and not set the owner yet or the mutex has been released.
270          */
271         return retval;
272 }
273 
274 /*
275  * Atomically try to take the lock when it is available
276  */
277 static inline bool mutex_try_to_acquire(struct mutex *lock)
278 {
279         return !mutex_is_locked(lock) &&
280                 (atomic_cmpxchg_acquire(&lock->count, 1, 0) == 1);
281 }
282 
283 /*
284  * Optimistic spinning.
285  *
286  * We try to spin for acquisition when we find that the lock owner
287  * is currently running on a (different) CPU and while we don't
288  * need to reschedule. The rationale is that if the lock owner is
289  * running, it is likely to release the lock soon.
290  *
291  * Since this needs the lock owner, and this mutex implementation
292  * doesn't track the owner atomically in the lock field, we need to
293  * track it non-atomically.
294  *
295  * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
296  * to serialize everything.
297  *
298  * The mutex spinners are queued up using MCS lock so that only one
299  * spinner can compete for the mutex. However, if mutex spinning isn't
300  * going to happen, there is no point in going through the lock/unlock
301  * overhead.
302  *
303  * Returns true when the lock was taken, otherwise false, indicating
304  * that we need to jump to the slowpath and sleep.
305  */
306 static bool mutex_optimistic_spin(struct mutex *lock,
307                                   struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
308 {
309         struct task_struct *task = current;
310 
311         if (!mutex_can_spin_on_owner(lock))
312                 goto done;
313 
314         /*
315          * In order to avoid a stampede of mutex spinners trying to
316          * acquire the mutex all at once, the spinners need to take a
317          * MCS (queued) lock first before spinning on the owner field.
318          */
319         if (!osq_lock(&lock->osq))
320                 goto done;
321 
322         while (true) {
323                 struct task_struct *owner;
324 
325                 if (use_ww_ctx && ww_ctx->acquired > 0) {
326                         struct ww_mutex *ww;
327 
328                         ww = container_of(lock, struct ww_mutex, base);
329                         /*
330                          * If ww->ctx is set the contents are undefined, only
331                          * by acquiring wait_lock there is a guarantee that
332                          * they are not invalid when reading.
333                          *
334                          * As such, when deadlock detection needs to be
335                          * performed the optimistic spinning cannot be done.
336                          */
337                         if (READ_ONCE(ww->ctx))
338                                 break;
339                 }
340 
341                 /*
342                  * If there's an owner, wait for it to either
343                  * release the lock or go to sleep.
344                  */
345                 owner = READ_ONCE(lock->owner);
346                 if (owner && !mutex_spin_on_owner(lock, owner))
347                         break;
348 
349                 /* Try to acquire the mutex if it is unlocked. */
350                 if (mutex_try_to_acquire(lock)) {
351                         lock_acquired(&lock->dep_map, ip);
352 
353                         if (use_ww_ctx) {
354                                 struct ww_mutex *ww;
355                                 ww = container_of(lock, struct ww_mutex, base);
356 
357                                 ww_mutex_set_context_fastpath(ww, ww_ctx);
358                         }
359 
360                         mutex_set_owner(lock);
361                         osq_unlock(&lock->osq);
362                         return true;
363                 }
364 
365                 /*
366                  * When there's no owner, we might have preempted between the
367                  * owner acquiring the lock and setting the owner field. If
368                  * we're an RT task that will live-lock because we won't let
369                  * the owner complete.
370                  */
371                 if (!owner && (need_resched() || rt_task(task)))
372                         break;
373 
374                 /*
375                  * The cpu_relax() call is a compiler barrier which forces
376                  * everything in this loop to be re-loaded. We don't need
377                  * memory barriers as we'll eventually observe the right
378                  * values at the cost of a few extra spins.
379                  */
380                 cpu_relax_lowlatency();
381         }
382 
383         osq_unlock(&lock->osq);
384 done:
385         /*
386          * If we fell out of the spin path because of need_resched(),
387          * reschedule now, before we try-lock the mutex. This avoids getting
388          * scheduled out right after we obtained the mutex.
389          */
390         if (need_resched()) {
391                 /*
392                  * We _should_ have TASK_RUNNING here, but just in case
393                  * we do not, make it so, otherwise we might get stuck.
394                  */
395                 __set_current_state(TASK_RUNNING);
396                 schedule_preempt_disabled();
397         }
398 
399         return false;
400 }
401 #else
402 static bool mutex_optimistic_spin(struct mutex *lock,
403                                   struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
404 {
405         return false;
406 }
407 #endif
408 
409 __visible __used noinline
410 void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
411 
412 /**
413  * mutex_unlock - release the mutex
414  * @lock: the mutex to be released
415  *
416  * Unlock a mutex that has been locked by this task previously.
417  *
418  * This function must not be used in interrupt context. Unlocking
419  * of a not locked mutex is not allowed.
420  *
421  * This function is similar to (but not equivalent to) up().
422  */
423 void __sched mutex_unlock(struct mutex *lock)
424 {
425         /*
426          * The unlocking fastpath is the 0->1 transition from 'locked'
427          * into 'unlocked' state:
428          */
429 #ifndef CONFIG_DEBUG_MUTEXES
430         /*
431          * When debugging is enabled we must not clear the owner before time,
432          * the slow path will always be taken, and that clears the owner field
433          * after verifying that it was indeed current.
434          */
435         mutex_clear_owner(lock);
436 #endif
437         __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
438 }
439 
440 EXPORT_SYMBOL(mutex_unlock);
441 
442 /**
443  * ww_mutex_unlock - release the w/w mutex
444  * @lock: the mutex to be released
445  *
446  * Unlock a mutex that has been locked by this task previously with any of the
447  * ww_mutex_lock* functions (with or without an acquire context). It is
448  * forbidden to release the locks after releasing the acquire context.
449  *
450  * This function must not be used in interrupt context. Unlocking
451  * of a unlocked mutex is not allowed.
452  */
453 void __sched ww_mutex_unlock(struct ww_mutex *lock)
454 {
455         /*
456          * The unlocking fastpath is the 0->1 transition from 'locked'
457          * into 'unlocked' state:
458          */
459         if (lock->ctx) {
460 #ifdef CONFIG_DEBUG_MUTEXES
461                 DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
462 #endif
463                 if (lock->ctx->acquired > 0)
464                         lock->ctx->acquired--;
465                 lock->ctx = NULL;
466         }
467 
468 #ifndef CONFIG_DEBUG_MUTEXES
469         /*
470          * When debugging is enabled we must not clear the owner before time,
471          * the slow path will always be taken, and that clears the owner field
472          * after verifying that it was indeed current.
473          */
474         mutex_clear_owner(&lock->base);
475 #endif
476         __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath);
477 }
478 EXPORT_SYMBOL(ww_mutex_unlock);
479 
480 static inline int __sched
481 __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
482 {
483         struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
484         struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
485 
486         if (!hold_ctx)
487                 return 0;
488 
489         if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
490             (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
491 #ifdef CONFIG_DEBUG_MUTEXES
492                 DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
493                 ctx->contending_lock = ww;
494 #endif
495                 return -EDEADLK;
496         }
497 
498         return 0;
499 }
500 
501 /*
502  * Lock a mutex (possibly interruptible), slowpath:
503  */
504 static __always_inline int __sched
505 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
506                     struct lockdep_map *nest_lock, unsigned long ip,
507                     struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
508 {
509         struct task_struct *task = current;
510         struct mutex_waiter waiter;
511         unsigned long flags;
512         int ret;
513 
514         if (use_ww_ctx) {
515                 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
516                 if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
517                         return -EALREADY;
518         }
519 
520         preempt_disable();
521         mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
522 
523         if (mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) {
524                 /* got the lock, yay! */
525                 preempt_enable();
526                 return 0;
527         }
528 
529         spin_lock_mutex(&lock->wait_lock, flags);
530 
531         /*
532          * Once more, try to acquire the lock. Only try-lock the mutex if
533          * it is unlocked to reduce unnecessary xchg() operations.
534          */
535         if (!mutex_is_locked(lock) &&
536             (atomic_xchg_acquire(&lock->count, 0) == 1))
537                 goto skip_wait;
538 
539         debug_mutex_lock_common(lock, &waiter);
540         debug_mutex_add_waiter(lock, &waiter, task);
541 
542         /* add waiting tasks to the end of the waitqueue (FIFO): */
543         list_add_tail(&waiter.list, &lock->wait_list);
544         waiter.task = task;
545 
546         lock_contended(&lock->dep_map, ip);
547 
548         for (;;) {
549                 /*
550                  * Lets try to take the lock again - this is needed even if
551                  * we get here for the first time (shortly after failing to
552                  * acquire the lock), to make sure that we get a wakeup once
553                  * it's unlocked. Later on, if we sleep, this is the
554                  * operation that gives us the lock. We xchg it to -1, so
555                  * that when we release the lock, we properly wake up the
556                  * other waiters. We only attempt the xchg if the count is
557                  * non-negative in order to avoid unnecessary xchg operations:
558                  */
559                 if (atomic_read(&lock->count) >= 0 &&
560                     (atomic_xchg_acquire(&lock->count, -1) == 1))
561                         break;
562 
563                 /*
564                  * got a signal? (This code gets eliminated in the
565                  * TASK_UNINTERRUPTIBLE case.)
566                  */
567                 if (unlikely(signal_pending_state(state, task))) {
568                         ret = -EINTR;
569                         goto err;
570                 }
571 
572                 if (use_ww_ctx && ww_ctx->acquired > 0) {
573                         ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);
574                         if (ret)
575                                 goto err;
576                 }
577 
578                 __set_task_state(task, state);
579 
580                 /* didn't get the lock, go to sleep: */
581                 spin_unlock_mutex(&lock->wait_lock, flags);
582                 schedule_preempt_disabled();
583                 spin_lock_mutex(&lock->wait_lock, flags);
584         }
585         __set_task_state(task, TASK_RUNNING);
586 
587         mutex_remove_waiter(lock, &waiter, task);
588         /* set it to 0 if there are no waiters left: */
589         if (likely(list_empty(&lock->wait_list)))
590                 atomic_set(&lock->count, 0);
591         debug_mutex_free_waiter(&waiter);
592 
593 skip_wait:
594         /* got the lock - cleanup and rejoice! */
595         lock_acquired(&lock->dep_map, ip);
596         mutex_set_owner(lock);
597 
598         if (use_ww_ctx) {
599                 struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
600                 ww_mutex_set_context_slowpath(ww, ww_ctx);
601         }
602 
603         spin_unlock_mutex(&lock->wait_lock, flags);
604         preempt_enable();
605         return 0;
606 
607 err:
608         mutex_remove_waiter(lock, &waiter, task);
609         spin_unlock_mutex(&lock->wait_lock, flags);
610         debug_mutex_free_waiter(&waiter);
611         mutex_release(&lock->dep_map, 1, ip);
612         preempt_enable();
613         return ret;
614 }
615 
616 #ifdef CONFIG_DEBUG_LOCK_ALLOC
617 void __sched
618 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
619 {
620         might_sleep();
621         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
622                             subclass, NULL, _RET_IP_, NULL, 0);
623 }
624 
625 EXPORT_SYMBOL_GPL(mutex_lock_nested);
626 
627 void __sched
628 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
629 {
630         might_sleep();
631         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
632                             0, nest, _RET_IP_, NULL, 0);
633 }
634 
635 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
636 
637 int __sched
638 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
639 {
640         might_sleep();
641         return __mutex_lock_common(lock, TASK_KILLABLE,
642                                    subclass, NULL, _RET_IP_, NULL, 0);
643 }
644 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
645 
646 int __sched
647 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
648 {
649         might_sleep();
650         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
651                                    subclass, NULL, _RET_IP_, NULL, 0);
652 }
653 
654 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
655 
656 static inline int
657 ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
658 {
659 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
660         unsigned tmp;
661 
662         if (ctx->deadlock_inject_countdown-- == 0) {
663                 tmp = ctx->deadlock_inject_interval;
664                 if (tmp > UINT_MAX/4)
665                         tmp = UINT_MAX;
666                 else
667                         tmp = tmp*2 + tmp + tmp/2;
668 
669                 ctx->deadlock_inject_interval = tmp;
670                 ctx->deadlock_inject_countdown = tmp;
671                 ctx->contending_lock = lock;
672 
673                 ww_mutex_unlock(lock);
674 
675                 return -EDEADLK;
676         }
677 #endif
678 
679         return 0;
680 }
681 
682 int __sched
683 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
684 {
685         int ret;
686 
687         might_sleep();
688         ret =  __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
689                                    0, &ctx->dep_map, _RET_IP_, ctx, 1);
690         if (!ret && ctx->acquired > 1)
691                 return ww_mutex_deadlock_injection(lock, ctx);
692 
693         return ret;
694 }
695 EXPORT_SYMBOL_GPL(__ww_mutex_lock);
696 
697 int __sched
698 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
699 {
700         int ret;
701 
702         might_sleep();
703         ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
704                                   0, &ctx->dep_map, _RET_IP_, ctx, 1);
705 
706         if (!ret && ctx->acquired > 1)
707                 return ww_mutex_deadlock_injection(lock, ctx);
708 
709         return ret;
710 }
711 EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
712 
713 #endif
714 
715 /*
716  * Release the lock, slowpath:
717  */
718 static inline void
719 __mutex_unlock_common_slowpath(struct mutex *lock, int nested)
720 {
721         unsigned long flags;
722         WAKE_Q(wake_q);
723 
724         /*
725          * As a performance measurement, release the lock before doing other
726          * wakeup related duties to follow. This allows other tasks to acquire
727          * the lock sooner, while still handling cleanups in past unlock calls.
728          * This can be done as we do not enforce strict equivalence between the
729          * mutex counter and wait_list.
730          *
731          *
732          * Some architectures leave the lock unlocked in the fastpath failure
733          * case, others need to leave it locked. In the later case we have to
734          * unlock it here - as the lock counter is currently 0 or negative.
735          */
736         if (__mutex_slowpath_needs_to_unlock())
737                 atomic_set(&lock->count, 1);
738 
739         spin_lock_mutex(&lock->wait_lock, flags);
740         mutex_release(&lock->dep_map, nested, _RET_IP_);
741         debug_mutex_unlock(lock);
742 
743         if (!list_empty(&lock->wait_list)) {
744                 /* get the first entry from the wait-list: */
745                 struct mutex_waiter *waiter =
746                                 list_entry(lock->wait_list.next,
747                                            struct mutex_waiter, list);
748 
749                 debug_mutex_wake_waiter(lock, waiter);
750                 wake_q_add(&wake_q, waiter->task);
751         }
752 
753         spin_unlock_mutex(&lock->wait_lock, flags);
754         wake_up_q(&wake_q);
755 }
756 
757 /*
758  * Release the lock, slowpath:
759  */
760 __visible void
761 __mutex_unlock_slowpath(atomic_t *lock_count)
762 {
763         struct mutex *lock = container_of(lock_count, struct mutex, count);
764 
765         __mutex_unlock_common_slowpath(lock, 1);
766 }
767 
768 #ifndef CONFIG_DEBUG_LOCK_ALLOC
769 /*
770  * Here come the less common (and hence less performance-critical) APIs:
771  * mutex_lock_interruptible() and mutex_trylock().
772  */
773 static noinline int __sched
774 __mutex_lock_killable_slowpath(struct mutex *lock);
775 
776 static noinline int __sched
777 __mutex_lock_interruptible_slowpath(struct mutex *lock);
778 
779 /**
780  * mutex_lock_interruptible - acquire the mutex, interruptible
781  * @lock: the mutex to be acquired
782  *
783  * Lock the mutex like mutex_lock(), and return 0 if the mutex has
784  * been acquired or sleep until the mutex becomes available. If a
785  * signal arrives while waiting for the lock then this function
786  * returns -EINTR.
787  *
788  * This function is similar to (but not equivalent to) down_interruptible().
789  */
790 int __sched mutex_lock_interruptible(struct mutex *lock)
791 {
792         int ret;
793 
794         might_sleep();
795         ret =  __mutex_fastpath_lock_retval(&lock->count);
796         if (likely(!ret)) {
797                 mutex_set_owner(lock);
798                 return 0;
799         } else
800                 return __mutex_lock_interruptible_slowpath(lock);
801 }
802 
803 EXPORT_SYMBOL(mutex_lock_interruptible);
804 
805 int __sched mutex_lock_killable(struct mutex *lock)
806 {
807         int ret;
808 
809         might_sleep();
810         ret = __mutex_fastpath_lock_retval(&lock->count);
811         if (likely(!ret)) {
812                 mutex_set_owner(lock);
813                 return 0;
814         } else
815                 return __mutex_lock_killable_slowpath(lock);
816 }
817 EXPORT_SYMBOL(mutex_lock_killable);
818 
819 __visible void __sched
820 __mutex_lock_slowpath(atomic_t *lock_count)
821 {
822         struct mutex *lock = container_of(lock_count, struct mutex, count);
823 
824         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
825                             NULL, _RET_IP_, NULL, 0);
826 }
827 
828 static noinline int __sched
829 __mutex_lock_killable_slowpath(struct mutex *lock)
830 {
831         return __mutex_lock_common(lock, TASK_KILLABLE, 0,
832                                    NULL, _RET_IP_, NULL, 0);
833 }
834 
835 static noinline int __sched
836 __mutex_lock_interruptible_slowpath(struct mutex *lock)
837 {
838         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
839                                    NULL, _RET_IP_, NULL, 0);
840 }
841 
842 static noinline int __sched
843 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
844 {
845         return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
846                                    NULL, _RET_IP_, ctx, 1);
847 }
848 
849 static noinline int __sched
850 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
851                                             struct ww_acquire_ctx *ctx)
852 {
853         return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
854                                    NULL, _RET_IP_, ctx, 1);
855 }
856 
857 #endif
858 
859 /*
860  * Spinlock based trylock, we take the spinlock and check whether we
861  * can get the lock:
862  */
863 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
864 {
865         struct mutex *lock = container_of(lock_count, struct mutex, count);
866         unsigned long flags;
867         int prev;
868 
869         /* No need to trylock if the mutex is locked. */
870         if (mutex_is_locked(lock))
871                 return 0;
872 
873         spin_lock_mutex(&lock->wait_lock, flags);
874 
875         prev = atomic_xchg_acquire(&lock->count, -1);
876         if (likely(prev == 1)) {
877                 mutex_set_owner(lock);
878                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
879         }
880 
881         /* Set it back to 0 if there are no waiters: */
882         if (likely(list_empty(&lock->wait_list)))
883                 atomic_set(&lock->count, 0);
884 
885         spin_unlock_mutex(&lock->wait_lock, flags);
886 
887         return prev == 1;
888 }
889 
890 /**
891  * mutex_trylock - try to acquire the mutex, without waiting
892  * @lock: the mutex to be acquired
893  *
894  * Try to acquire the mutex atomically. Returns 1 if the mutex
895  * has been acquired successfully, and 0 on contention.
896  *
897  * NOTE: this function follows the spin_trylock() convention, so
898  * it is negated from the down_trylock() return values! Be careful
899  * about this when converting semaphore users to mutexes.
900  *
901  * This function must not be used in interrupt context. The
902  * mutex must be released by the same task that acquired it.
903  */
904 int __sched mutex_trylock(struct mutex *lock)
905 {
906         int ret;
907 
908         ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
909         if (ret)
910                 mutex_set_owner(lock);
911 
912         return ret;
913 }
914 EXPORT_SYMBOL(mutex_trylock);
915 
916 #ifndef CONFIG_DEBUG_LOCK_ALLOC
917 int __sched
918 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
919 {
920         int ret;
921 
922         might_sleep();
923 
924         ret = __mutex_fastpath_lock_retval(&lock->base.count);
925 
926         if (likely(!ret)) {
927                 ww_mutex_set_context_fastpath(lock, ctx);
928                 mutex_set_owner(&lock->base);
929         } else
930                 ret = __ww_mutex_lock_slowpath(lock, ctx);
931         return ret;
932 }
933 EXPORT_SYMBOL(__ww_mutex_lock);
934 
935 int __sched
936 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
937 {
938         int ret;
939 
940         might_sleep();
941 
942         ret = __mutex_fastpath_lock_retval(&lock->base.count);
943 
944         if (likely(!ret)) {
945                 ww_mutex_set_context_fastpath(lock, ctx);
946                 mutex_set_owner(&lock->base);
947         } else
948                 ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx);
949         return ret;
950 }
951 EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
952 
953 #endif
954 
955 /**
956  * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
957  * @cnt: the atomic which we are to dec
958  * @lock: the mutex to return holding if we dec to 0
959  *
960  * return true and hold lock if we dec to 0, return false otherwise
961  */
962 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
963 {
964         /* dec if we can't possibly hit 0 */
965         if (atomic_add_unless(cnt, -1, 1))
966                 return 0;
967         /* we might hit 0, so take the lock */
968         mutex_lock(lock);
969         if (!atomic_dec_and_test(cnt)) {
970                 /* when we actually did the dec, we didn't hit 0 */
971                 mutex_unlock(lock);
972                 return 0;
973         }
974         /* we hit 0, and we hold the lock */
975         return 1;
976 }
977 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
978 

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