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
__mutex_init(struct mutex * lock,const char * name,struct lock_class_key * key)40 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
41 {
42 	atomic_long_set(&lock->owner, 0);
43 	spin_lock_init(&lock->wait_lock);
44 	INIT_LIST_HEAD(&lock->wait_list);
45 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
46 	osq_lock_init(&lock->osq);
47 #endif
48 
49 	debug_mutex_init(lock, name, key);
50 }
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  */
__mutex_owner(struct mutex * lock)73 static inline struct task_struct *__mutex_owner(struct mutex *lock)
74 {
75 	return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
76 }
77 
__owner_task(unsigned long owner)78 static inline struct task_struct *__owner_task(unsigned long owner)
79 {
80 	return (struct task_struct *)(owner & ~MUTEX_FLAGS);
81 }
82 
mutex_is_locked(struct mutex * lock)83 bool mutex_is_locked(struct mutex *lock)
84 {
85 	return __mutex_owner(lock) != NULL;
86 }
87 EXPORT_SYMBOL(mutex_is_locked);
88 
89 __must_check enum mutex_trylock_recursive_enum
mutex_trylock_recursive(struct mutex * lock)90 mutex_trylock_recursive(struct mutex *lock)
91 {
92 	if (unlikely(__mutex_owner(lock) == current))
93 		return MUTEX_TRYLOCK_RECURSIVE;
94 
95 	return mutex_trylock(lock);
96 }
97 EXPORT_SYMBOL(mutex_trylock_recursive);
98 
__owner_flags(unsigned long owner)99 static inline unsigned long __owner_flags(unsigned long owner)
100 {
101 	return owner & MUTEX_FLAGS;
102 }
103 
104 /*
105  * Trylock variant that retuns the owning task on failure.
106  */
__mutex_trylock_or_owner(struct mutex * lock)107 static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
108 {
109 	unsigned long owner, curr = (unsigned long)current;
110 
111 	owner = atomic_long_read(&lock->owner);
112 	for (;;) { /* must loop, can race against a flag */
113 		unsigned long old, flags = __owner_flags(owner);
114 		unsigned long task = owner & ~MUTEX_FLAGS;
115 
116 		if (task) {
117 			if (likely(task != curr))
118 				break;
119 
120 			if (likely(!(flags & MUTEX_FLAG_PICKUP)))
121 				break;
122 
123 			flags &= ~MUTEX_FLAG_PICKUP;
124 		} else {
125 #ifdef CONFIG_DEBUG_MUTEXES
126 			DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
127 #endif
128 		}
129 
130 		/*
131 		 * We set the HANDOFF bit, we must make sure it doesn't live
132 		 * past the point where we acquire it. This would be possible
133 		 * if we (accidentally) set the bit on an unlocked mutex.
134 		 */
135 		flags &= ~MUTEX_FLAG_HANDOFF;
136 
137 		old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
138 		if (old == owner)
139 			return NULL;
140 
141 		owner = old;
142 	}
143 
144 	return __owner_task(owner);
145 }
146 
147 /*
148  * Actual trylock that will work on any unlocked state.
149  */
__mutex_trylock(struct mutex * lock)150 static inline bool __mutex_trylock(struct mutex *lock)
151 {
152 	return !__mutex_trylock_or_owner(lock);
153 }
154 
155 #ifndef CONFIG_DEBUG_LOCK_ALLOC
156 /*
157  * Lockdep annotations are contained to the slow paths for simplicity.
158  * There is nothing that would stop spreading the lockdep annotations outwards
159  * except more code.
160  */
161 
162 /*
163  * Optimistic trylock that only works in the uncontended case. Make sure to
164  * follow with a __mutex_trylock() before failing.
165  */
__mutex_trylock_fast(struct mutex * lock)166 static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
167 {
168 	unsigned long curr = (unsigned long)current;
169 	unsigned long zero = 0UL;
170 
171 	if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr))
172 		return true;
173 
174 	return false;
175 }
176 
__mutex_unlock_fast(struct mutex * lock)177 static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
178 {
179 	unsigned long curr = (unsigned long)current;
180 
181 	if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
182 		return true;
183 
184 	return false;
185 }
186 #endif
187 
__mutex_set_flag(struct mutex * lock,unsigned long flag)188 static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
189 {
190 	atomic_long_or(flag, &lock->owner);
191 }
192 
__mutex_clear_flag(struct mutex * lock,unsigned long flag)193 static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
194 {
195 	atomic_long_andnot(flag, &lock->owner);
196 }
197 
__mutex_waiter_is_first(struct mutex * lock,struct mutex_waiter * waiter)198 static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
199 {
200 	return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
201 }
202 
203 /*
204  * Add @waiter to a given location in the lock wait_list and set the
205  * FLAG_WAITERS flag if it's the first waiter.
206  */
207 static void __sched
__mutex_add_waiter(struct mutex * lock,struct mutex_waiter * waiter,struct list_head * list)208 __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
209 		   struct list_head *list)
210 {
211 	debug_mutex_add_waiter(lock, waiter, current);
212 
213 	list_add_tail(&waiter->list, list);
214 	if (__mutex_waiter_is_first(lock, waiter))
215 		__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
216 }
217 
218 /*
219  * Give up ownership to a specific task, when @task = NULL, this is equivalent
220  * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
221  * WAITERS. Provides RELEASE semantics like a regular unlock, the
222  * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
223  */
__mutex_handoff(struct mutex * lock,struct task_struct * task)224 static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
225 {
226 	unsigned long owner = atomic_long_read(&lock->owner);
227 
228 	for (;;) {
229 		unsigned long old, new;
230 
231 #ifdef CONFIG_DEBUG_MUTEXES
232 		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
233 		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
234 #endif
235 
236 		new = (owner & MUTEX_FLAG_WAITERS);
237 		new |= (unsigned long)task;
238 		if (task)
239 			new |= MUTEX_FLAG_PICKUP;
240 
241 		old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
242 		if (old == owner)
243 			break;
244 
245 		owner = old;
246 	}
247 }
248 
249 #ifndef CONFIG_DEBUG_LOCK_ALLOC
250 /*
251  * We split the mutex lock/unlock logic into separate fastpath and
252  * slowpath functions, to reduce the register pressure on the fastpath.
253  * We also put the fastpath first in the kernel image, to make sure the
254  * branch is predicted by the CPU as default-untaken.
255  */
256 static void __sched __mutex_lock_slowpath(struct mutex *lock);
257 
258 /**
259  * mutex_lock - acquire the mutex
260  * @lock: the mutex to be acquired
261  *
262  * Lock the mutex exclusively for this task. If the mutex is not
263  * available right now, it will sleep until it can get it.
264  *
265  * The mutex must later on be released by the same task that
266  * acquired it. Recursive locking is not allowed. The task
267  * may not exit without first unlocking the mutex. Also, kernel
268  * memory where the mutex resides must not be freed with
269  * the mutex still locked. The mutex must first be initialized
270  * (or statically defined) before it can be locked. memset()-ing
271  * the mutex to 0 is not allowed.
272  *
273  * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
274  * checks that will enforce the restrictions and will also do
275  * deadlock debugging)
276  *
277  * This function is similar to (but not equivalent to) down().
278  */
mutex_lock(struct mutex * lock)279 void __sched mutex_lock(struct mutex *lock)
280 {
281 	might_sleep();
282 
283 	if (!__mutex_trylock_fast(lock))
284 		__mutex_lock_slowpath(lock);
285 }
286 EXPORT_SYMBOL(mutex_lock);
287 #endif
288 
289 /*
290  * Wait-Die:
291  *   The newer transactions are killed when:
292  *     It (the new transaction) makes a request for a lock being held
293  *     by an older transaction.
294  *
295  * Wound-Wait:
296  *   The newer transactions are wounded when:
297  *     An older transaction makes a request for a lock being held by
298  *     the newer transaction.
299  */
300 
301 /*
302  * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
303  * it.
304  */
305 static __always_inline void
ww_mutex_lock_acquired(struct ww_mutex * ww,struct ww_acquire_ctx * ww_ctx)306 ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
307 {
308 #ifdef CONFIG_DEBUG_MUTEXES
309 	/*
310 	 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
311 	 * but released with a normal mutex_unlock in this call.
312 	 *
313 	 * This should never happen, always use ww_mutex_unlock.
314 	 */
315 	DEBUG_LOCKS_WARN_ON(ww->ctx);
316 
317 	/*
318 	 * Not quite done after calling ww_acquire_done() ?
319 	 */
320 	DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
321 
322 	if (ww_ctx->contending_lock) {
323 		/*
324 		 * After -EDEADLK you tried to
325 		 * acquire a different ww_mutex? Bad!
326 		 */
327 		DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
328 
329 		/*
330 		 * You called ww_mutex_lock after receiving -EDEADLK,
331 		 * but 'forgot' to unlock everything else first?
332 		 */
333 		DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
334 		ww_ctx->contending_lock = NULL;
335 	}
336 
337 	/*
338 	 * Naughty, using a different class will lead to undefined behavior!
339 	 */
340 	DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
341 #endif
342 	ww_ctx->acquired++;
343 	ww->ctx = ww_ctx;
344 }
345 
346 /*
347  * Determine if context @a is 'after' context @b. IOW, @a is a younger
348  * transaction than @b and depending on algorithm either needs to wait for
349  * @b or die.
350  */
351 static inline bool __sched
__ww_ctx_stamp_after(struct ww_acquire_ctx * a,struct ww_acquire_ctx * b)352 __ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
353 {
354 
355 	return (signed long)(a->stamp - b->stamp) > 0;
356 }
357 
358 /*
359  * Wait-Die; wake a younger waiter context (when locks held) such that it can
360  * die.
361  *
362  * Among waiters with context, only the first one can have other locks acquired
363  * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
364  * __ww_mutex_check_kill() wake any but the earliest context.
365  */
366 static bool __sched
__ww_mutex_die(struct mutex * lock,struct mutex_waiter * waiter,struct ww_acquire_ctx * ww_ctx)367 __ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter,
368 	       struct ww_acquire_ctx *ww_ctx)
369 {
370 	if (!ww_ctx->is_wait_die)
371 		return false;
372 
373 	if (waiter->ww_ctx->acquired > 0 &&
374 			__ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) {
375 		debug_mutex_wake_waiter(lock, waiter);
376 		wake_up_process(waiter->task);
377 	}
378 
379 	return true;
380 }
381 
382 /*
383  * Wound-Wait; wound a younger @hold_ctx if it holds the lock.
384  *
385  * Wound the lock holder if there are waiters with older transactions than
386  * the lock holders. Even if multiple waiters may wound the lock holder,
387  * it's sufficient that only one does.
388  */
__ww_mutex_wound(struct mutex * lock,struct ww_acquire_ctx * ww_ctx,struct ww_acquire_ctx * hold_ctx)389 static bool __ww_mutex_wound(struct mutex *lock,
390 			     struct ww_acquire_ctx *ww_ctx,
391 			     struct ww_acquire_ctx *hold_ctx)
392 {
393 	struct task_struct *owner = __mutex_owner(lock);
394 
395 	lockdep_assert_held(&lock->wait_lock);
396 
397 	/*
398 	 * Possible through __ww_mutex_add_waiter() when we race with
399 	 * ww_mutex_set_context_fastpath(). In that case we'll get here again
400 	 * through __ww_mutex_check_waiters().
401 	 */
402 	if (!hold_ctx)
403 		return false;
404 
405 	/*
406 	 * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
407 	 * it cannot go away because we'll have FLAG_WAITERS set and hold
408 	 * wait_lock.
409 	 */
410 	if (!owner)
411 		return false;
412 
413 	if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) {
414 		hold_ctx->wounded = 1;
415 
416 		/*
417 		 * wake_up_process() paired with set_current_state()
418 		 * inserts sufficient barriers to make sure @owner either sees
419 		 * it's wounded in __ww_mutex_check_kill() or has a
420 		 * wakeup pending to re-read the wounded state.
421 		 */
422 		if (owner != current)
423 			wake_up_process(owner);
424 
425 		return true;
426 	}
427 
428 	return false;
429 }
430 
431 /*
432  * We just acquired @lock under @ww_ctx, if there are later contexts waiting
433  * behind us on the wait-list, check if they need to die, or wound us.
434  *
435  * See __ww_mutex_add_waiter() for the list-order construction; basically the
436  * list is ordered by stamp, smallest (oldest) first.
437  *
438  * This relies on never mixing wait-die/wound-wait on the same wait-list;
439  * which is currently ensured by that being a ww_class property.
440  *
441  * The current task must not be on the wait list.
442  */
443 static void __sched
__ww_mutex_check_waiters(struct mutex * lock,struct ww_acquire_ctx * ww_ctx)444 __ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
445 {
446 	struct mutex_waiter *cur;
447 
448 	lockdep_assert_held(&lock->wait_lock);
449 
450 	list_for_each_entry(cur, &lock->wait_list, list) {
451 		if (!cur->ww_ctx)
452 			continue;
453 
454 		if (__ww_mutex_die(lock, cur, ww_ctx) ||
455 		    __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
456 			break;
457 	}
458 }
459 
460 /*
461  * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
462  * and wake up any waiters so they can recheck.
463  */
464 static __always_inline void
ww_mutex_set_context_fastpath(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)465 ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
466 {
467 	ww_mutex_lock_acquired(lock, ctx);
468 
469 	/*
470 	 * The lock->ctx update should be visible on all cores before
471 	 * the WAITERS check is done, otherwise contended waiters might be
472 	 * missed. The contended waiters will either see ww_ctx == NULL
473 	 * and keep spinning, or it will acquire wait_lock, add itself
474 	 * to waiter list and sleep.
475 	 */
476 	smp_mb(); /* See comments above and below. */
477 
478 	/*
479 	 * [W] ww->ctx = ctx	    [W] MUTEX_FLAG_WAITERS
480 	 *     MB		        MB
481 	 * [R] MUTEX_FLAG_WAITERS   [R] ww->ctx
482 	 *
483 	 * The memory barrier above pairs with the memory barrier in
484 	 * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
485 	 * and/or !empty list.
486 	 */
487 	if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
488 		return;
489 
490 	/*
491 	 * Uh oh, we raced in fastpath, check if any of the waiters need to
492 	 * die or wound us.
493 	 */
494 	spin_lock(&lock->base.wait_lock);
495 	__ww_mutex_check_waiters(&lock->base, ctx);
496 	spin_unlock(&lock->base.wait_lock);
497 }
498 
499 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
500 
501 static inline
ww_mutex_spin_on_owner(struct mutex * lock,struct ww_acquire_ctx * ww_ctx,struct mutex_waiter * waiter)502 bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
503 			    struct mutex_waiter *waiter)
504 {
505 	struct ww_mutex *ww;
506 
507 	ww = container_of(lock, struct ww_mutex, base);
508 
509 	/*
510 	 * If ww->ctx is set the contents are undefined, only
511 	 * by acquiring wait_lock there is a guarantee that
512 	 * they are not invalid when reading.
513 	 *
514 	 * As such, when deadlock detection needs to be
515 	 * performed the optimistic spinning cannot be done.
516 	 *
517 	 * Check this in every inner iteration because we may
518 	 * be racing against another thread's ww_mutex_lock.
519 	 */
520 	if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
521 		return false;
522 
523 	/*
524 	 * If we aren't on the wait list yet, cancel the spin
525 	 * if there are waiters. We want  to avoid stealing the
526 	 * lock from a waiter with an earlier stamp, since the
527 	 * other thread may already own a lock that we also
528 	 * need.
529 	 */
530 	if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
531 		return false;
532 
533 	/*
534 	 * Similarly, stop spinning if we are no longer the
535 	 * first waiter.
536 	 */
537 	if (waiter && !__mutex_waiter_is_first(lock, waiter))
538 		return false;
539 
540 	return true;
541 }
542 
543 /*
544  * Look out! "owner" is an entirely speculative pointer access and not
545  * reliable.
546  *
547  * "noinline" so that this function shows up on perf profiles.
548  */
549 static noinline
mutex_spin_on_owner(struct mutex * lock,struct task_struct * owner,struct ww_acquire_ctx * ww_ctx,struct mutex_waiter * waiter)550 bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
551 			 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
552 {
553 	bool ret = true;
554 
555 	rcu_read_lock();
556 	while (__mutex_owner(lock) == owner) {
557 		/*
558 		 * Ensure we emit the owner->on_cpu, dereference _after_
559 		 * checking lock->owner still matches owner. If that fails,
560 		 * owner might point to freed memory. If it still matches,
561 		 * the rcu_read_lock() ensures the memory stays valid.
562 		 */
563 		barrier();
564 
565 		/*
566 		 * Use vcpu_is_preempted to detect lock holder preemption issue.
567 		 */
568 		if (!owner->on_cpu || need_resched() ||
569 				vcpu_is_preempted(task_cpu(owner))) {
570 			ret = false;
571 			break;
572 		}
573 
574 		if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
575 			ret = false;
576 			break;
577 		}
578 
579 		cpu_relax();
580 	}
581 	rcu_read_unlock();
582 
583 	return ret;
584 }
585 
586 /*
587  * Initial check for entering the mutex spinning loop
588  */
mutex_can_spin_on_owner(struct mutex * lock)589 static inline int mutex_can_spin_on_owner(struct mutex *lock)
590 {
591 	struct task_struct *owner;
592 	int retval = 1;
593 
594 	if (need_resched())
595 		return 0;
596 
597 	rcu_read_lock();
598 	owner = __mutex_owner(lock);
599 
600 	/*
601 	 * As lock holder preemption issue, we both skip spinning if task is not
602 	 * on cpu or its cpu is preempted
603 	 */
604 	if (owner)
605 		retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
606 	rcu_read_unlock();
607 
608 	/*
609 	 * If lock->owner is not set, the mutex has been released. Return true
610 	 * such that we'll trylock in the spin path, which is a faster option
611 	 * than the blocking slow path.
612 	 */
613 	return retval;
614 }
615 
616 /*
617  * Optimistic spinning.
618  *
619  * We try to spin for acquisition when we find that the lock owner
620  * is currently running on a (different) CPU and while we don't
621  * need to reschedule. The rationale is that if the lock owner is
622  * running, it is likely to release the lock soon.
623  *
624  * The mutex spinners are queued up using MCS lock so that only one
625  * spinner can compete for the mutex. However, if mutex spinning isn't
626  * going to happen, there is no point in going through the lock/unlock
627  * overhead.
628  *
629  * Returns true when the lock was taken, otherwise false, indicating
630  * that we need to jump to the slowpath and sleep.
631  *
632  * The waiter flag is set to true if the spinner is a waiter in the wait
633  * queue. The waiter-spinner will spin on the lock directly and concurrently
634  * with the spinner at the head of the OSQ, if present, until the owner is
635  * changed to itself.
636  */
637 static __always_inline bool
mutex_optimistic_spin(struct mutex * lock,struct ww_acquire_ctx * ww_ctx,const bool use_ww_ctx,struct mutex_waiter * waiter)638 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
639 		      const bool use_ww_ctx, struct mutex_waiter *waiter)
640 {
641 	if (!waiter) {
642 		/*
643 		 * The purpose of the mutex_can_spin_on_owner() function is
644 		 * to eliminate the overhead of osq_lock() and osq_unlock()
645 		 * in case spinning isn't possible. As a waiter-spinner
646 		 * is not going to take OSQ lock anyway, there is no need
647 		 * to call mutex_can_spin_on_owner().
648 		 */
649 		if (!mutex_can_spin_on_owner(lock))
650 			goto fail;
651 
652 		/*
653 		 * In order to avoid a stampede of mutex spinners trying to
654 		 * acquire the mutex all at once, the spinners need to take a
655 		 * MCS (queued) lock first before spinning on the owner field.
656 		 */
657 		if (!osq_lock(&lock->osq))
658 			goto fail;
659 	}
660 
661 	for (;;) {
662 		struct task_struct *owner;
663 
664 		/* Try to acquire the mutex... */
665 		owner = __mutex_trylock_or_owner(lock);
666 		if (!owner)
667 			break;
668 
669 		/*
670 		 * There's an owner, wait for it to either
671 		 * release the lock or go to sleep.
672 		 */
673 		if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
674 			goto fail_unlock;
675 
676 		/*
677 		 * The cpu_relax() call is a compiler barrier which forces
678 		 * everything in this loop to be re-loaded. We don't need
679 		 * memory barriers as we'll eventually observe the right
680 		 * values at the cost of a few extra spins.
681 		 */
682 		cpu_relax();
683 	}
684 
685 	if (!waiter)
686 		osq_unlock(&lock->osq);
687 
688 	return true;
689 
690 
691 fail_unlock:
692 	if (!waiter)
693 		osq_unlock(&lock->osq);
694 
695 fail:
696 	/*
697 	 * If we fell out of the spin path because of need_resched(),
698 	 * reschedule now, before we try-lock the mutex. This avoids getting
699 	 * scheduled out right after we obtained the mutex.
700 	 */
701 	if (need_resched()) {
702 		/*
703 		 * We _should_ have TASK_RUNNING here, but just in case
704 		 * we do not, make it so, otherwise we might get stuck.
705 		 */
706 		__set_current_state(TASK_RUNNING);
707 		schedule_preempt_disabled();
708 	}
709 
710 	return false;
711 }
712 #else
713 static __always_inline bool
mutex_optimistic_spin(struct mutex * lock,struct ww_acquire_ctx * ww_ctx,const bool use_ww_ctx,struct mutex_waiter * waiter)714 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
715 		      const bool use_ww_ctx, struct mutex_waiter *waiter)
716 {
717 	return false;
718 }
719 #endif
720 
721 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
722 
723 /**
724  * mutex_unlock - release the mutex
725  * @lock: the mutex to be released
726  *
727  * Unlock a mutex that has been locked by this task previously.
728  *
729  * This function must not be used in interrupt context. Unlocking
730  * of a not locked mutex is not allowed.
731  *
732  * This function is similar to (but not equivalent to) up().
733  */
mutex_unlock(struct mutex * lock)734 void __sched mutex_unlock(struct mutex *lock)
735 {
736 #ifndef CONFIG_DEBUG_LOCK_ALLOC
737 	if (__mutex_unlock_fast(lock))
738 		return;
739 #endif
740 	__mutex_unlock_slowpath(lock, _RET_IP_);
741 }
742 EXPORT_SYMBOL(mutex_unlock);
743 
744 /**
745  * ww_mutex_unlock - release the w/w mutex
746  * @lock: the mutex to be released
747  *
748  * Unlock a mutex that has been locked by this task previously with any of the
749  * ww_mutex_lock* functions (with or without an acquire context). It is
750  * forbidden to release the locks after releasing the acquire context.
751  *
752  * This function must not be used in interrupt context. Unlocking
753  * of a unlocked mutex is not allowed.
754  */
ww_mutex_unlock(struct ww_mutex * lock)755 void __sched ww_mutex_unlock(struct ww_mutex *lock)
756 {
757 	/*
758 	 * The unlocking fastpath is the 0->1 transition from 'locked'
759 	 * into 'unlocked' state:
760 	 */
761 	if (lock->ctx) {
762 #ifdef CONFIG_DEBUG_MUTEXES
763 		DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
764 #endif
765 		if (lock->ctx->acquired > 0)
766 			lock->ctx->acquired--;
767 		lock->ctx = NULL;
768 	}
769 
770 	mutex_unlock(&lock->base);
771 }
772 EXPORT_SYMBOL(ww_mutex_unlock);
773 
774 
775 static __always_inline int __sched
__ww_mutex_kill(struct mutex * lock,struct ww_acquire_ctx * ww_ctx)776 __ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
777 {
778 	if (ww_ctx->acquired > 0) {
779 #ifdef CONFIG_DEBUG_MUTEXES
780 		struct ww_mutex *ww;
781 
782 		ww = container_of(lock, struct ww_mutex, base);
783 		DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
784 		ww_ctx->contending_lock = ww;
785 #endif
786 		return -EDEADLK;
787 	}
788 
789 	return 0;
790 }
791 
792 
793 /*
794  * Check the wound condition for the current lock acquire.
795  *
796  * Wound-Wait: If we're wounded, kill ourself.
797  *
798  * Wait-Die: If we're trying to acquire a lock already held by an older
799  *           context, kill ourselves.
800  *
801  * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
802  * look at waiters before us in the wait-list.
803  */
804 static inline int __sched
__ww_mutex_check_kill(struct mutex * lock,struct mutex_waiter * waiter,struct ww_acquire_ctx * ctx)805 __ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter,
806 		      struct ww_acquire_ctx *ctx)
807 {
808 	struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
809 	struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
810 	struct mutex_waiter *cur;
811 
812 	if (ctx->acquired == 0)
813 		return 0;
814 
815 	if (!ctx->is_wait_die) {
816 		if (ctx->wounded)
817 			return __ww_mutex_kill(lock, ctx);
818 
819 		return 0;
820 	}
821 
822 	if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
823 		return __ww_mutex_kill(lock, ctx);
824 
825 	/*
826 	 * If there is a waiter in front of us that has a context, then its
827 	 * stamp is earlier than ours and we must kill ourself.
828 	 */
829 	cur = waiter;
830 	list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
831 		if (!cur->ww_ctx)
832 			continue;
833 
834 		return __ww_mutex_kill(lock, ctx);
835 	}
836 
837 	return 0;
838 }
839 
840 /*
841  * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
842  * first. Such that older contexts are preferred to acquire the lock over
843  * younger contexts.
844  *
845  * Waiters without context are interspersed in FIFO order.
846  *
847  * Furthermore, for Wait-Die kill ourself immediately when possible (there are
848  * older contexts already waiting) to avoid unnecessary waiting and for
849  * Wound-Wait ensure we wound the owning context when it is younger.
850  */
851 static inline int __sched
__ww_mutex_add_waiter(struct mutex_waiter * waiter,struct mutex * lock,struct ww_acquire_ctx * ww_ctx)852 __ww_mutex_add_waiter(struct mutex_waiter *waiter,
853 		      struct mutex *lock,
854 		      struct ww_acquire_ctx *ww_ctx)
855 {
856 	struct mutex_waiter *cur;
857 	struct list_head *pos;
858 	bool is_wait_die;
859 
860 	if (!ww_ctx) {
861 		__mutex_add_waiter(lock, waiter, &lock->wait_list);
862 		return 0;
863 	}
864 
865 	is_wait_die = ww_ctx->is_wait_die;
866 
867 	/*
868 	 * Add the waiter before the first waiter with a higher stamp.
869 	 * Waiters without a context are skipped to avoid starving
870 	 * them. Wait-Die waiters may die here. Wound-Wait waiters
871 	 * never die here, but they are sorted in stamp order and
872 	 * may wound the lock holder.
873 	 */
874 	pos = &lock->wait_list;
875 	list_for_each_entry_reverse(cur, &lock->wait_list, list) {
876 		if (!cur->ww_ctx)
877 			continue;
878 
879 		if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
880 			/*
881 			 * Wait-Die: if we find an older context waiting, there
882 			 * is no point in queueing behind it, as we'd have to
883 			 * die the moment it would acquire the lock.
884 			 */
885 			if (is_wait_die) {
886 				int ret = __ww_mutex_kill(lock, ww_ctx);
887 
888 				if (ret)
889 					return ret;
890 			}
891 
892 			break;
893 		}
894 
895 		pos = &cur->list;
896 
897 		/* Wait-Die: ensure younger waiters die. */
898 		__ww_mutex_die(lock, cur, ww_ctx);
899 	}
900 
901 	__mutex_add_waiter(lock, waiter, pos);
902 
903 	/*
904 	 * Wound-Wait: if we're blocking on a mutex owned by a younger context,
905 	 * wound that such that we might proceed.
906 	 */
907 	if (!is_wait_die) {
908 		struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
909 
910 		/*
911 		 * See ww_mutex_set_context_fastpath(). Orders setting
912 		 * MUTEX_FLAG_WAITERS vs the ww->ctx load,
913 		 * such that either we or the fastpath will wound @ww->ctx.
914 		 */
915 		smp_mb();
916 		__ww_mutex_wound(lock, ww_ctx, ww->ctx);
917 	}
918 
919 	return 0;
920 }
921 
922 /*
923  * Lock a mutex (possibly interruptible), slowpath:
924  */
925 static __always_inline int __sched
__mutex_lock_common(struct mutex * lock,long state,unsigned int subclass,struct lockdep_map * nest_lock,unsigned long ip,struct ww_acquire_ctx * ww_ctx,const bool use_ww_ctx)926 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
927 		    struct lockdep_map *nest_lock, unsigned long ip,
928 		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
929 {
930 	struct mutex_waiter waiter;
931 	bool first = false;
932 	struct ww_mutex *ww;
933 	int ret;
934 
935 	might_sleep();
936 
937 #ifdef CONFIG_DEBUG_MUTEXES
938 	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
939 #endif
940 
941 	ww = container_of(lock, struct ww_mutex, base);
942 	if (use_ww_ctx && ww_ctx) {
943 		if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
944 			return -EALREADY;
945 
946 		/*
947 		 * Reset the wounded flag after a kill. No other process can
948 		 * race and wound us here since they can't have a valid owner
949 		 * pointer if we don't have any locks held.
950 		 */
951 		if (ww_ctx->acquired == 0)
952 			ww_ctx->wounded = 0;
953 	}
954 
955 	preempt_disable();
956 	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
957 
958 	if (__mutex_trylock(lock) ||
959 	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
960 		/* got the lock, yay! */
961 		lock_acquired(&lock->dep_map, ip);
962 		if (use_ww_ctx && ww_ctx)
963 			ww_mutex_set_context_fastpath(ww, ww_ctx);
964 		preempt_enable();
965 		return 0;
966 	}
967 
968 	spin_lock(&lock->wait_lock);
969 	/*
970 	 * After waiting to acquire the wait_lock, try again.
971 	 */
972 	if (__mutex_trylock(lock)) {
973 		if (use_ww_ctx && ww_ctx)
974 			__ww_mutex_check_waiters(lock, ww_ctx);
975 
976 		goto skip_wait;
977 	}
978 
979 	debug_mutex_lock_common(lock, &waiter);
980 
981 	lock_contended(&lock->dep_map, ip);
982 
983 	if (!use_ww_ctx) {
984 		/* add waiting tasks to the end of the waitqueue (FIFO): */
985 		__mutex_add_waiter(lock, &waiter, &lock->wait_list);
986 
987 
988 #ifdef CONFIG_DEBUG_MUTEXES
989 		waiter.ww_ctx = MUTEX_POISON_WW_CTX;
990 #endif
991 	} else {
992 		/*
993 		 * Add in stamp order, waking up waiters that must kill
994 		 * themselves.
995 		 */
996 		ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
997 		if (ret)
998 			goto err_early_kill;
999 
1000 		waiter.ww_ctx = ww_ctx;
1001 	}
1002 
1003 	waiter.task = current;
1004 
1005 	set_current_state(state);
1006 	for (;;) {
1007 		/*
1008 		 * Once we hold wait_lock, we're serialized against
1009 		 * mutex_unlock() handing the lock off to us, do a trylock
1010 		 * before testing the error conditions to make sure we pick up
1011 		 * the handoff.
1012 		 */
1013 		if (__mutex_trylock(lock))
1014 			goto acquired;
1015 
1016 		/*
1017 		 * Check for signals and kill conditions while holding
1018 		 * wait_lock. This ensures the lock cancellation is ordered
1019 		 * against mutex_unlock() and wake-ups do not go missing.
1020 		 */
1021 		if (signal_pending_state(state, current)) {
1022 			ret = -EINTR;
1023 			goto err;
1024 		}
1025 
1026 		if (use_ww_ctx && ww_ctx) {
1027 			ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
1028 			if (ret)
1029 				goto err;
1030 		}
1031 
1032 		spin_unlock(&lock->wait_lock);
1033 		schedule_preempt_disabled();
1034 
1035 		/*
1036 		 * ww_mutex needs to always recheck its position since its waiter
1037 		 * list is not FIFO ordered.
1038 		 */
1039 		if ((use_ww_ctx && ww_ctx) || !first) {
1040 			first = __mutex_waiter_is_first(lock, &waiter);
1041 			if (first)
1042 				__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
1043 		}
1044 
1045 		set_current_state(state);
1046 		/*
1047 		 * Here we order against unlock; we must either see it change
1048 		 * state back to RUNNING and fall through the next schedule(),
1049 		 * or we must see its unlock and acquire.
1050 		 */
1051 		if (__mutex_trylock(lock) ||
1052 		    (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
1053 			break;
1054 
1055 		spin_lock(&lock->wait_lock);
1056 	}
1057 	spin_lock(&lock->wait_lock);
1058 acquired:
1059 	__set_current_state(TASK_RUNNING);
1060 
1061 	if (use_ww_ctx && ww_ctx) {
1062 		/*
1063 		 * Wound-Wait; we stole the lock (!first_waiter), check the
1064 		 * waiters as anyone might want to wound us.
1065 		 */
1066 		if (!ww_ctx->is_wait_die &&
1067 		    !__mutex_waiter_is_first(lock, &waiter))
1068 			__ww_mutex_check_waiters(lock, ww_ctx);
1069 	}
1070 
1071 	mutex_remove_waiter(lock, &waiter, current);
1072 	if (likely(list_empty(&lock->wait_list)))
1073 		__mutex_clear_flag(lock, MUTEX_FLAGS);
1074 
1075 	debug_mutex_free_waiter(&waiter);
1076 
1077 skip_wait:
1078 	/* got the lock - cleanup and rejoice! */
1079 	lock_acquired(&lock->dep_map, ip);
1080 
1081 	if (use_ww_ctx && ww_ctx)
1082 		ww_mutex_lock_acquired(ww, ww_ctx);
1083 
1084 	spin_unlock(&lock->wait_lock);
1085 	preempt_enable();
1086 	return 0;
1087 
1088 err:
1089 	__set_current_state(TASK_RUNNING);
1090 	mutex_remove_waiter(lock, &waiter, current);
1091 err_early_kill:
1092 	spin_unlock(&lock->wait_lock);
1093 	debug_mutex_free_waiter(&waiter);
1094 	mutex_release(&lock->dep_map, ip);
1095 	preempt_enable();
1096 	return ret;
1097 }
1098 
1099 static int __sched
__mutex_lock(struct mutex * lock,long state,unsigned int subclass,struct lockdep_map * nest_lock,unsigned long ip)1100 __mutex_lock(struct mutex *lock, long state, unsigned int subclass,
1101 	     struct lockdep_map *nest_lock, unsigned long ip)
1102 {
1103 	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
1104 }
1105 
1106 static int __sched
__ww_mutex_lock(struct mutex * lock,long state,unsigned int subclass,struct lockdep_map * nest_lock,unsigned long ip,struct ww_acquire_ctx * ww_ctx)1107 __ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
1108 		struct lockdep_map *nest_lock, unsigned long ip,
1109 		struct ww_acquire_ctx *ww_ctx)
1110 {
1111 	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
1112 }
1113 
1114 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1115 void __sched
mutex_lock_nested(struct mutex * lock,unsigned int subclass)1116 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
1117 {
1118 	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
1119 }
1120 
1121 EXPORT_SYMBOL_GPL(mutex_lock_nested);
1122 
1123 void __sched
_mutex_lock_nest_lock(struct mutex * lock,struct lockdep_map * nest)1124 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
1125 {
1126 	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
1127 }
1128 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
1129 
1130 int __sched
mutex_lock_killable_nested(struct mutex * lock,unsigned int subclass)1131 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
1132 {
1133 	return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
1134 }
1135 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
1136 
1137 int __sched
mutex_lock_interruptible_nested(struct mutex * lock,unsigned int subclass)1138 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
1139 {
1140 	return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
1141 }
1142 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
1143 
1144 void __sched
mutex_lock_io_nested(struct mutex * lock,unsigned int subclass)1145 mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
1146 {
1147 	int token;
1148 
1149 	might_sleep();
1150 
1151 	token = io_schedule_prepare();
1152 	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
1153 			    subclass, NULL, _RET_IP_, NULL, 0);
1154 	io_schedule_finish(token);
1155 }
1156 EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
1157 
1158 static inline int
ww_mutex_deadlock_injection(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)1159 ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1160 {
1161 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
1162 	unsigned tmp;
1163 
1164 	if (ctx->deadlock_inject_countdown-- == 0) {
1165 		tmp = ctx->deadlock_inject_interval;
1166 		if (tmp > UINT_MAX/4)
1167 			tmp = UINT_MAX;
1168 		else
1169 			tmp = tmp*2 + tmp + tmp/2;
1170 
1171 		ctx->deadlock_inject_interval = tmp;
1172 		ctx->deadlock_inject_countdown = tmp;
1173 		ctx->contending_lock = lock;
1174 
1175 		ww_mutex_unlock(lock);
1176 
1177 		return -EDEADLK;
1178 	}
1179 #endif
1180 
1181 	return 0;
1182 }
1183 
1184 int __sched
ww_mutex_lock(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)1185 ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1186 {
1187 	int ret;
1188 
1189 	might_sleep();
1190 	ret =  __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
1191 			       0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
1192 			       ctx);
1193 	if (!ret && ctx && ctx->acquired > 1)
1194 		return ww_mutex_deadlock_injection(lock, ctx);
1195 
1196 	return ret;
1197 }
1198 EXPORT_SYMBOL_GPL(ww_mutex_lock);
1199 
1200 int __sched
ww_mutex_lock_interruptible(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)1201 ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1202 {
1203 	int ret;
1204 
1205 	might_sleep();
1206 	ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
1207 			      0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
1208 			      ctx);
1209 
1210 	if (!ret && ctx && ctx->acquired > 1)
1211 		return ww_mutex_deadlock_injection(lock, ctx);
1212 
1213 	return ret;
1214 }
1215 EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
1216 
1217 #endif
1218 
1219 /*
1220  * Release the lock, slowpath:
1221  */
__mutex_unlock_slowpath(struct mutex * lock,unsigned long ip)1222 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
1223 {
1224 	struct task_struct *next = NULL;
1225 	DEFINE_WAKE_Q(wake_q);
1226 	unsigned long owner;
1227 
1228 	mutex_release(&lock->dep_map, ip);
1229 
1230 	/*
1231 	 * Release the lock before (potentially) taking the spinlock such that
1232 	 * other contenders can get on with things ASAP.
1233 	 *
1234 	 * Except when HANDOFF, in that case we must not clear the owner field,
1235 	 * but instead set it to the top waiter.
1236 	 */
1237 	owner = atomic_long_read(&lock->owner);
1238 	for (;;) {
1239 		unsigned long old;
1240 
1241 #ifdef CONFIG_DEBUG_MUTEXES
1242 		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
1243 		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
1244 #endif
1245 
1246 		if (owner & MUTEX_FLAG_HANDOFF)
1247 			break;
1248 
1249 		old = atomic_long_cmpxchg_release(&lock->owner, owner,
1250 						  __owner_flags(owner));
1251 		if (old == owner) {
1252 			if (owner & MUTEX_FLAG_WAITERS)
1253 				break;
1254 
1255 			return;
1256 		}
1257 
1258 		owner = old;
1259 	}
1260 
1261 	spin_lock(&lock->wait_lock);
1262 	debug_mutex_unlock(lock);
1263 	if (!list_empty(&lock->wait_list)) {
1264 		/* get the first entry from the wait-list: */
1265 		struct mutex_waiter *waiter =
1266 			list_first_entry(&lock->wait_list,
1267 					 struct mutex_waiter, list);
1268 
1269 		next = waiter->task;
1270 
1271 		debug_mutex_wake_waiter(lock, waiter);
1272 		wake_q_add(&wake_q, next);
1273 	}
1274 
1275 	if (owner & MUTEX_FLAG_HANDOFF)
1276 		__mutex_handoff(lock, next);
1277 
1278 	spin_unlock(&lock->wait_lock);
1279 
1280 	wake_up_q(&wake_q);
1281 }
1282 
1283 #ifndef CONFIG_DEBUG_LOCK_ALLOC
1284 /*
1285  * Here come the less common (and hence less performance-critical) APIs:
1286  * mutex_lock_interruptible() and mutex_trylock().
1287  */
1288 static noinline int __sched
1289 __mutex_lock_killable_slowpath(struct mutex *lock);
1290 
1291 static noinline int __sched
1292 __mutex_lock_interruptible_slowpath(struct mutex *lock);
1293 
1294 /**
1295  * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
1296  * @lock: The mutex to be acquired.
1297  *
1298  * Lock the mutex like mutex_lock().  If a signal is delivered while the
1299  * process is sleeping, this function will return without acquiring the
1300  * mutex.
1301  *
1302  * Context: Process context.
1303  * Return: 0 if the lock was successfully acquired or %-EINTR if a
1304  * signal arrived.
1305  */
mutex_lock_interruptible(struct mutex * lock)1306 int __sched mutex_lock_interruptible(struct mutex *lock)
1307 {
1308 	might_sleep();
1309 
1310 	if (__mutex_trylock_fast(lock))
1311 		return 0;
1312 
1313 	return __mutex_lock_interruptible_slowpath(lock);
1314 }
1315 
1316 EXPORT_SYMBOL(mutex_lock_interruptible);
1317 
1318 /**
1319  * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
1320  * @lock: The mutex to be acquired.
1321  *
1322  * Lock the mutex like mutex_lock().  If a signal which will be fatal to
1323  * the current process is delivered while the process is sleeping, this
1324  * function will return without acquiring the mutex.
1325  *
1326  * Context: Process context.
1327  * Return: 0 if the lock was successfully acquired or %-EINTR if a
1328  * fatal signal arrived.
1329  */
mutex_lock_killable(struct mutex * lock)1330 int __sched mutex_lock_killable(struct mutex *lock)
1331 {
1332 	might_sleep();
1333 
1334 	if (__mutex_trylock_fast(lock))
1335 		return 0;
1336 
1337 	return __mutex_lock_killable_slowpath(lock);
1338 }
1339 EXPORT_SYMBOL(mutex_lock_killable);
1340 
1341 /**
1342  * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1343  * @lock: The mutex to be acquired.
1344  *
1345  * Lock the mutex like mutex_lock().  While the task is waiting for this
1346  * mutex, it will be accounted as being in the IO wait state by the
1347  * scheduler.
1348  *
1349  * Context: Process context.
1350  */
mutex_lock_io(struct mutex * lock)1351 void __sched mutex_lock_io(struct mutex *lock)
1352 {
1353 	int token;
1354 
1355 	token = io_schedule_prepare();
1356 	mutex_lock(lock);
1357 	io_schedule_finish(token);
1358 }
1359 EXPORT_SYMBOL_GPL(mutex_lock_io);
1360 
1361 static noinline void __sched
__mutex_lock_slowpath(struct mutex * lock)1362 __mutex_lock_slowpath(struct mutex *lock)
1363 {
1364 	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1365 }
1366 
1367 static noinline int __sched
__mutex_lock_killable_slowpath(struct mutex * lock)1368 __mutex_lock_killable_slowpath(struct mutex *lock)
1369 {
1370 	return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
1371 }
1372 
1373 static noinline int __sched
__mutex_lock_interruptible_slowpath(struct mutex * lock)1374 __mutex_lock_interruptible_slowpath(struct mutex *lock)
1375 {
1376 	return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
1377 }
1378 
1379 static noinline int __sched
__ww_mutex_lock_slowpath(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)1380 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1381 {
1382 	return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
1383 			       _RET_IP_, ctx);
1384 }
1385 
1386 static noinline int __sched
__ww_mutex_lock_interruptible_slowpath(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)1387 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1388 					    struct ww_acquire_ctx *ctx)
1389 {
1390 	return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
1391 			       _RET_IP_, ctx);
1392 }
1393 
1394 #endif
1395 
1396 /**
1397  * mutex_trylock - try to acquire the mutex, without waiting
1398  * @lock: the mutex to be acquired
1399  *
1400  * Try to acquire the mutex atomically. Returns 1 if the mutex
1401  * has been acquired successfully, and 0 on contention.
1402  *
1403  * NOTE: this function follows the spin_trylock() convention, so
1404  * it is negated from the down_trylock() return values! Be careful
1405  * about this when converting semaphore users to mutexes.
1406  *
1407  * This function must not be used in interrupt context. The
1408  * mutex must be released by the same task that acquired it.
1409  */
mutex_trylock(struct mutex * lock)1410 int __sched mutex_trylock(struct mutex *lock)
1411 {
1412 	bool locked;
1413 
1414 #ifdef CONFIG_DEBUG_MUTEXES
1415 	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
1416 #endif
1417 
1418 	locked = __mutex_trylock(lock);
1419 	if (locked)
1420 		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1421 
1422 	return locked;
1423 }
1424 EXPORT_SYMBOL(mutex_trylock);
1425 
1426 #ifndef CONFIG_DEBUG_LOCK_ALLOC
1427 int __sched
ww_mutex_lock(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)1428 ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1429 {
1430 	might_sleep();
1431 
1432 	if (__mutex_trylock_fast(&lock->base)) {
1433 		if (ctx)
1434 			ww_mutex_set_context_fastpath(lock, ctx);
1435 		return 0;
1436 	}
1437 
1438 	return __ww_mutex_lock_slowpath(lock, ctx);
1439 }
1440 EXPORT_SYMBOL(ww_mutex_lock);
1441 
1442 int __sched
ww_mutex_lock_interruptible(struct ww_mutex * lock,struct ww_acquire_ctx * ctx)1443 ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1444 {
1445 	might_sleep();
1446 
1447 	if (__mutex_trylock_fast(&lock->base)) {
1448 		if (ctx)
1449 			ww_mutex_set_context_fastpath(lock, ctx);
1450 		return 0;
1451 	}
1452 
1453 	return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
1454 }
1455 EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1456 
1457 #endif
1458 
1459 /**
1460  * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1461  * @cnt: the atomic which we are to dec
1462  * @lock: the mutex to return holding if we dec to 0
1463  *
1464  * return true and hold lock if we dec to 0, return false otherwise
1465  */
atomic_dec_and_mutex_lock(atomic_t * cnt,struct mutex * lock)1466 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1467 {
1468 	/* dec if we can't possibly hit 0 */
1469 	if (atomic_add_unless(cnt, -1, 1))
1470 		return 0;
1471 	/* we might hit 0, so take the lock */
1472 	mutex_lock(lock);
1473 	if (!atomic_dec_and_test(cnt)) {
1474 		/* when we actually did the dec, we didn't hit 0 */
1475 		mutex_unlock(lock);
1476 		return 0;
1477 	}
1478 	/* we hit 0, and we hold the lock */
1479 	return 1;
1480 }
1481 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
1482