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6053ee3b | 1 | /* |
67a6de49 | 2 | * kernel/locking/mutex.c |
6053ee3b IM |
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 | * | |
0d66bf6d PZ |
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 | * | |
214e0aed | 18 | * Also see Documentation/locking/mutex-design.txt. |
6053ee3b IM |
19 | */ |
20 | #include <linux/mutex.h> | |
1b375dc3 | 21 | #include <linux/ww_mutex.h> |
6053ee3b | 22 | #include <linux/sched.h> |
8bd75c77 | 23 | #include <linux/sched/rt.h> |
9984de1a | 24 | #include <linux/export.h> |
6053ee3b IM |
25 | #include <linux/spinlock.h> |
26 | #include <linux/interrupt.h> | |
9a11b49a | 27 | #include <linux/debug_locks.h> |
7a215f89 | 28 | #include <linux/osq_lock.h> |
6053ee3b | 29 | |
6053ee3b IM |
30 | #ifdef CONFIG_DEBUG_MUTEXES |
31 | # include "mutex-debug.h" | |
6053ee3b IM |
32 | #else |
33 | # include "mutex.h" | |
6053ee3b IM |
34 | #endif |
35 | ||
ef5d4707 IM |
36 | void |
37 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) | |
6053ee3b | 38 | { |
3ca0ff57 | 39 | atomic_long_set(&lock->owner, 0); |
6053ee3b IM |
40 | spin_lock_init(&lock->wait_lock); |
41 | INIT_LIST_HEAD(&lock->wait_list); | |
2bd2c92c | 42 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
4d9d951e | 43 | osq_lock_init(&lock->osq); |
2bd2c92c | 44 | #endif |
6053ee3b | 45 | |
ef5d4707 | 46 | debug_mutex_init(lock, name, key); |
6053ee3b | 47 | } |
6053ee3b IM |
48 | EXPORT_SYMBOL(__mutex_init); |
49 | ||
3ca0ff57 PZ |
50 | /* |
51 | * @owner: contains: 'struct task_struct *' to the current lock owner, | |
52 | * NULL means not owned. Since task_struct pointers are aligned at | |
53 | * ARCH_MIN_TASKALIGN (which is at least sizeof(void *)), we have low | |
54 | * bits to store extra state. | |
55 | * | |
56 | * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup. | |
9d659ae1 | 57 | * Bit1 indicates unlock needs to hand the lock to the top-waiter |
3ca0ff57 PZ |
58 | */ |
59 | #define MUTEX_FLAG_WAITERS 0x01 | |
9d659ae1 | 60 | #define MUTEX_FLAG_HANDOFF 0x02 |
3ca0ff57 PZ |
61 | |
62 | #define MUTEX_FLAGS 0x03 | |
63 | ||
64 | static inline struct task_struct *__owner_task(unsigned long owner) | |
65 | { | |
66 | return (struct task_struct *)(owner & ~MUTEX_FLAGS); | |
67 | } | |
68 | ||
69 | static inline unsigned long __owner_flags(unsigned long owner) | |
70 | { | |
71 | return owner & MUTEX_FLAGS; | |
72 | } | |
73 | ||
74 | /* | |
75 | * Actual trylock that will work on any unlocked state. | |
9d659ae1 PZ |
76 | * |
77 | * When setting the owner field, we must preserve the low flag bits. | |
78 | * | |
79 | * Be careful with @handoff, only set that in a wait-loop (where you set | |
80 | * HANDOFF) to avoid recursive lock attempts. | |
3ca0ff57 | 81 | */ |
9d659ae1 | 82 | static inline bool __mutex_trylock(struct mutex *lock, const bool handoff) |
3ca0ff57 PZ |
83 | { |
84 | unsigned long owner, curr = (unsigned long)current; | |
85 | ||
86 | owner = atomic_long_read(&lock->owner); | |
87 | for (;;) { /* must loop, can race against a flag */ | |
9d659ae1 PZ |
88 | unsigned long old, flags = __owner_flags(owner); |
89 | ||
90 | if (__owner_task(owner)) { | |
91 | if (handoff && unlikely(__owner_task(owner) == current)) { | |
92 | /* | |
93 | * Provide ACQUIRE semantics for the lock-handoff. | |
94 | * | |
95 | * We cannot easily use load-acquire here, since | |
96 | * the actual load is a failed cmpxchg, which | |
97 | * doesn't imply any barriers. | |
98 | * | |
99 | * Also, this is a fairly unlikely scenario, and | |
100 | * this contains the cost. | |
101 | */ | |
102 | smp_mb(); /* ACQUIRE */ | |
103 | return true; | |
104 | } | |
3ca0ff57 | 105 | |
3ca0ff57 | 106 | return false; |
9d659ae1 PZ |
107 | } |
108 | ||
109 | /* | |
110 | * We set the HANDOFF bit, we must make sure it doesn't live | |
111 | * past the point where we acquire it. This would be possible | |
112 | * if we (accidentally) set the bit on an unlocked mutex. | |
113 | */ | |
114 | if (handoff) | |
115 | flags &= ~MUTEX_FLAG_HANDOFF; | |
3ca0ff57 | 116 | |
9d659ae1 | 117 | old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags); |
3ca0ff57 PZ |
118 | if (old == owner) |
119 | return true; | |
120 | ||
121 | owner = old; | |
122 | } | |
123 | } | |
124 | ||
125 | #ifndef CONFIG_DEBUG_LOCK_ALLOC | |
126 | /* | |
127 | * Lockdep annotations are contained to the slow paths for simplicity. | |
128 | * There is nothing that would stop spreading the lockdep annotations outwards | |
129 | * except more code. | |
130 | */ | |
131 | ||
132 | /* | |
133 | * Optimistic trylock that only works in the uncontended case. Make sure to | |
134 | * follow with a __mutex_trylock() before failing. | |
135 | */ | |
136 | static __always_inline bool __mutex_trylock_fast(struct mutex *lock) | |
137 | { | |
138 | unsigned long curr = (unsigned long)current; | |
139 | ||
140 | if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr)) | |
141 | return true; | |
142 | ||
143 | return false; | |
144 | } | |
145 | ||
146 | static __always_inline bool __mutex_unlock_fast(struct mutex *lock) | |
147 | { | |
148 | unsigned long curr = (unsigned long)current; | |
149 | ||
150 | if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr) | |
151 | return true; | |
152 | ||
153 | return false; | |
154 | } | |
155 | #endif | |
156 | ||
157 | static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag) | |
158 | { | |
159 | atomic_long_or(flag, &lock->owner); | |
160 | } | |
161 | ||
162 | static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag) | |
163 | { | |
164 | atomic_long_andnot(flag, &lock->owner); | |
165 | } | |
166 | ||
9d659ae1 PZ |
167 | static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter) |
168 | { | |
169 | return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter; | |
170 | } | |
171 | ||
172 | /* | |
173 | * Give up ownership to a specific task, when @task = NULL, this is equivalent | |
174 | * to a regular unlock. Clears HANDOFF, preserves WAITERS. Provides RELEASE | |
175 | * semantics like a regular unlock, the __mutex_trylock() provides matching | |
176 | * ACQUIRE semantics for the handoff. | |
177 | */ | |
178 | static void __mutex_handoff(struct mutex *lock, struct task_struct *task) | |
179 | { | |
180 | unsigned long owner = atomic_long_read(&lock->owner); | |
181 | ||
182 | for (;;) { | |
183 | unsigned long old, new; | |
184 | ||
185 | #ifdef CONFIG_DEBUG_MUTEXES | |
186 | DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current); | |
187 | #endif | |
188 | ||
189 | new = (owner & MUTEX_FLAG_WAITERS); | |
190 | new |= (unsigned long)task; | |
191 | ||
192 | old = atomic_long_cmpxchg_release(&lock->owner, owner, new); | |
193 | if (old == owner) | |
194 | break; | |
195 | ||
196 | owner = old; | |
197 | } | |
198 | } | |
199 | ||
e4564f79 | 200 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
201 | /* |
202 | * We split the mutex lock/unlock logic into separate fastpath and | |
203 | * slowpath functions, to reduce the register pressure on the fastpath. | |
204 | * We also put the fastpath first in the kernel image, to make sure the | |
205 | * branch is predicted by the CPU as default-untaken. | |
206 | */ | |
3ca0ff57 | 207 | static void __sched __mutex_lock_slowpath(struct mutex *lock); |
6053ee3b | 208 | |
ef5dc121 | 209 | /** |
6053ee3b IM |
210 | * mutex_lock - acquire the mutex |
211 | * @lock: the mutex to be acquired | |
212 | * | |
213 | * Lock the mutex exclusively for this task. If the mutex is not | |
214 | * available right now, it will sleep until it can get it. | |
215 | * | |
216 | * The mutex must later on be released by the same task that | |
217 | * acquired it. Recursive locking is not allowed. The task | |
218 | * may not exit without first unlocking the mutex. Also, kernel | |
139b6fd2 | 219 | * memory where the mutex resides must not be freed with |
6053ee3b IM |
220 | * the mutex still locked. The mutex must first be initialized |
221 | * (or statically defined) before it can be locked. memset()-ing | |
222 | * the mutex to 0 is not allowed. | |
223 | * | |
224 | * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging | |
225 | * checks that will enforce the restrictions and will also do | |
226 | * deadlock debugging. ) | |
227 | * | |
228 | * This function is similar to (but not equivalent to) down(). | |
229 | */ | |
b09d2501 | 230 | void __sched mutex_lock(struct mutex *lock) |
6053ee3b | 231 | { |
c544bdb1 | 232 | might_sleep(); |
6053ee3b | 233 | |
3ca0ff57 PZ |
234 | if (!__mutex_trylock_fast(lock)) |
235 | __mutex_lock_slowpath(lock); | |
236 | } | |
6053ee3b | 237 | EXPORT_SYMBOL(mutex_lock); |
e4564f79 | 238 | #endif |
6053ee3b | 239 | |
76916515 DB |
240 | static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww, |
241 | struct ww_acquire_ctx *ww_ctx) | |
242 | { | |
243 | #ifdef CONFIG_DEBUG_MUTEXES | |
244 | /* | |
245 | * If this WARN_ON triggers, you used ww_mutex_lock to acquire, | |
246 | * but released with a normal mutex_unlock in this call. | |
247 | * | |
248 | * This should never happen, always use ww_mutex_unlock. | |
249 | */ | |
250 | DEBUG_LOCKS_WARN_ON(ww->ctx); | |
251 | ||
252 | /* | |
253 | * Not quite done after calling ww_acquire_done() ? | |
254 | */ | |
255 | DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire); | |
256 | ||
257 | if (ww_ctx->contending_lock) { | |
258 | /* | |
259 | * After -EDEADLK you tried to | |
260 | * acquire a different ww_mutex? Bad! | |
261 | */ | |
262 | DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww); | |
263 | ||
264 | /* | |
265 | * You called ww_mutex_lock after receiving -EDEADLK, | |
266 | * but 'forgot' to unlock everything else first? | |
267 | */ | |
268 | DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0); | |
269 | ww_ctx->contending_lock = NULL; | |
270 | } | |
271 | ||
272 | /* | |
273 | * Naughty, using a different class will lead to undefined behavior! | |
274 | */ | |
275 | DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class); | |
276 | #endif | |
277 | ww_ctx->acquired++; | |
278 | } | |
279 | ||
280 | /* | |
4bd19084 | 281 | * After acquiring lock with fastpath or when we lost out in contested |
76916515 | 282 | * slowpath, set ctx and wake up any waiters so they can recheck. |
76916515 DB |
283 | */ |
284 | static __always_inline void | |
285 | ww_mutex_set_context_fastpath(struct ww_mutex *lock, | |
286 | struct ww_acquire_ctx *ctx) | |
287 | { | |
288 | unsigned long flags; | |
289 | struct mutex_waiter *cur; | |
290 | ||
291 | ww_mutex_lock_acquired(lock, ctx); | |
292 | ||
293 | lock->ctx = ctx; | |
294 | ||
295 | /* | |
296 | * The lock->ctx update should be visible on all cores before | |
297 | * the atomic read is done, otherwise contended waiters might be | |
298 | * missed. The contended waiters will either see ww_ctx == NULL | |
299 | * and keep spinning, or it will acquire wait_lock, add itself | |
300 | * to waiter list and sleep. | |
301 | */ | |
302 | smp_mb(); /* ^^^ */ | |
303 | ||
304 | /* | |
305 | * Check if lock is contended, if not there is nobody to wake up | |
306 | */ | |
3ca0ff57 | 307 | if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS))) |
76916515 DB |
308 | return; |
309 | ||
310 | /* | |
311 | * Uh oh, we raced in fastpath, wake up everyone in this case, | |
312 | * so they can see the new lock->ctx. | |
313 | */ | |
314 | spin_lock_mutex(&lock->base.wait_lock, flags); | |
315 | list_for_each_entry(cur, &lock->base.wait_list, list) { | |
316 | debug_mutex_wake_waiter(&lock->base, cur); | |
317 | wake_up_process(cur->task); | |
318 | } | |
319 | spin_unlock_mutex(&lock->base.wait_lock, flags); | |
320 | } | |
321 | ||
4bd19084 DB |
322 | /* |
323 | * After acquiring lock in the slowpath set ctx and wake up any | |
324 | * waiters so they can recheck. | |
325 | * | |
326 | * Callers must hold the mutex wait_lock. | |
327 | */ | |
328 | static __always_inline void | |
329 | ww_mutex_set_context_slowpath(struct ww_mutex *lock, | |
330 | struct ww_acquire_ctx *ctx) | |
331 | { | |
332 | struct mutex_waiter *cur; | |
333 | ||
334 | ww_mutex_lock_acquired(lock, ctx); | |
335 | lock->ctx = ctx; | |
336 | ||
337 | /* | |
338 | * Give any possible sleeping processes the chance to wake up, | |
339 | * so they can recheck if they have to back off. | |
340 | */ | |
341 | list_for_each_entry(cur, &lock->base.wait_list, list) { | |
342 | debug_mutex_wake_waiter(&lock->base, cur); | |
343 | wake_up_process(cur->task); | |
344 | } | |
345 | } | |
76916515 | 346 | |
41fcb9f2 | 347 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
41fcb9f2 WL |
348 | /* |
349 | * Look out! "owner" is an entirely speculative pointer | |
350 | * access and not reliable. | |
351 | */ | |
352 | static noinline | |
be1f7bf2 | 353 | bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) |
41fcb9f2 | 354 | { |
01ac33c1 | 355 | bool ret = true; |
be1f7bf2 | 356 | |
41fcb9f2 | 357 | rcu_read_lock(); |
3ca0ff57 | 358 | while (__mutex_owner(lock) == owner) { |
be1f7bf2 JL |
359 | /* |
360 | * Ensure we emit the owner->on_cpu, dereference _after_ | |
01ac33c1 JL |
361 | * checking lock->owner still matches owner. If that fails, |
362 | * owner might point to freed memory. If it still matches, | |
be1f7bf2 JL |
363 | * the rcu_read_lock() ensures the memory stays valid. |
364 | */ | |
365 | barrier(); | |
366 | ||
367 | if (!owner->on_cpu || need_resched()) { | |
368 | ret = false; | |
369 | break; | |
370 | } | |
41fcb9f2 | 371 | |
3a6bfbc9 | 372 | cpu_relax_lowlatency(); |
41fcb9f2 WL |
373 | } |
374 | rcu_read_unlock(); | |
375 | ||
be1f7bf2 | 376 | return ret; |
41fcb9f2 | 377 | } |
2bd2c92c WL |
378 | |
379 | /* | |
380 | * Initial check for entering the mutex spinning loop | |
381 | */ | |
382 | static inline int mutex_can_spin_on_owner(struct mutex *lock) | |
383 | { | |
1e40c2ed | 384 | struct task_struct *owner; |
2bd2c92c WL |
385 | int retval = 1; |
386 | ||
46af29e4 JL |
387 | if (need_resched()) |
388 | return 0; | |
389 | ||
2bd2c92c | 390 | rcu_read_lock(); |
3ca0ff57 | 391 | owner = __mutex_owner(lock); |
1e40c2ed PZ |
392 | if (owner) |
393 | retval = owner->on_cpu; | |
2bd2c92c | 394 | rcu_read_unlock(); |
3ca0ff57 | 395 | |
2bd2c92c | 396 | /* |
3ca0ff57 PZ |
397 | * If lock->owner is not set, the mutex has been released. Return true |
398 | * such that we'll trylock in the spin path, which is a faster option | |
399 | * than the blocking slow path. | |
2bd2c92c WL |
400 | */ |
401 | return retval; | |
402 | } | |
76916515 | 403 | |
76916515 DB |
404 | /* |
405 | * Optimistic spinning. | |
406 | * | |
407 | * We try to spin for acquisition when we find that the lock owner | |
408 | * is currently running on a (different) CPU and while we don't | |
409 | * need to reschedule. The rationale is that if the lock owner is | |
410 | * running, it is likely to release the lock soon. | |
411 | * | |
76916515 DB |
412 | * The mutex spinners are queued up using MCS lock so that only one |
413 | * spinner can compete for the mutex. However, if mutex spinning isn't | |
414 | * going to happen, there is no point in going through the lock/unlock | |
415 | * overhead. | |
416 | * | |
417 | * Returns true when the lock was taken, otherwise false, indicating | |
418 | * that we need to jump to the slowpath and sleep. | |
419 | */ | |
420 | static bool mutex_optimistic_spin(struct mutex *lock, | |
421 | struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) | |
422 | { | |
423 | struct task_struct *task = current; | |
424 | ||
425 | if (!mutex_can_spin_on_owner(lock)) | |
426 | goto done; | |
427 | ||
e42f678a DB |
428 | /* |
429 | * In order to avoid a stampede of mutex spinners trying to | |
430 | * acquire the mutex all at once, the spinners need to take a | |
431 | * MCS (queued) lock first before spinning on the owner field. | |
432 | */ | |
76916515 DB |
433 | if (!osq_lock(&lock->osq)) |
434 | goto done; | |
435 | ||
436 | while (true) { | |
437 | struct task_struct *owner; | |
438 | ||
439 | if (use_ww_ctx && ww_ctx->acquired > 0) { | |
440 | struct ww_mutex *ww; | |
441 | ||
442 | ww = container_of(lock, struct ww_mutex, base); | |
443 | /* | |
444 | * If ww->ctx is set the contents are undefined, only | |
445 | * by acquiring wait_lock there is a guarantee that | |
446 | * they are not invalid when reading. | |
447 | * | |
448 | * As such, when deadlock detection needs to be | |
449 | * performed the optimistic spinning cannot be done. | |
450 | */ | |
4d3199e4 | 451 | if (READ_ONCE(ww->ctx)) |
76916515 DB |
452 | break; |
453 | } | |
454 | ||
455 | /* | |
456 | * If there's an owner, wait for it to either | |
457 | * release the lock or go to sleep. | |
458 | */ | |
3ca0ff57 | 459 | owner = __mutex_owner(lock); |
76916515 DB |
460 | if (owner && !mutex_spin_on_owner(lock, owner)) |
461 | break; | |
462 | ||
463 | /* Try to acquire the mutex if it is unlocked. */ | |
9d659ae1 | 464 | if (__mutex_trylock(lock, false)) { |
76916515 DB |
465 | osq_unlock(&lock->osq); |
466 | return true; | |
467 | } | |
468 | ||
76916515 DB |
469 | /* |
470 | * The cpu_relax() call is a compiler barrier which forces | |
471 | * everything in this loop to be re-loaded. We don't need | |
472 | * memory barriers as we'll eventually observe the right | |
473 | * values at the cost of a few extra spins. | |
474 | */ | |
475 | cpu_relax_lowlatency(); | |
476 | } | |
477 | ||
478 | osq_unlock(&lock->osq); | |
479 | done: | |
480 | /* | |
481 | * If we fell out of the spin path because of need_resched(), | |
482 | * reschedule now, before we try-lock the mutex. This avoids getting | |
483 | * scheduled out right after we obtained the mutex. | |
484 | */ | |
6f942a1f PZ |
485 | if (need_resched()) { |
486 | /* | |
487 | * We _should_ have TASK_RUNNING here, but just in case | |
488 | * we do not, make it so, otherwise we might get stuck. | |
489 | */ | |
490 | __set_current_state(TASK_RUNNING); | |
76916515 | 491 | schedule_preempt_disabled(); |
6f942a1f | 492 | } |
76916515 DB |
493 | |
494 | return false; | |
495 | } | |
496 | #else | |
497 | static bool mutex_optimistic_spin(struct mutex *lock, | |
498 | struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) | |
499 | { | |
500 | return false; | |
501 | } | |
41fcb9f2 WL |
502 | #endif |
503 | ||
3ca0ff57 | 504 | static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip); |
6053ee3b | 505 | |
ef5dc121 | 506 | /** |
6053ee3b IM |
507 | * mutex_unlock - release the mutex |
508 | * @lock: the mutex to be released | |
509 | * | |
510 | * Unlock a mutex that has been locked by this task previously. | |
511 | * | |
512 | * This function must not be used in interrupt context. Unlocking | |
513 | * of a not locked mutex is not allowed. | |
514 | * | |
515 | * This function is similar to (but not equivalent to) up(). | |
516 | */ | |
7ad5b3a5 | 517 | void __sched mutex_unlock(struct mutex *lock) |
6053ee3b | 518 | { |
3ca0ff57 PZ |
519 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
520 | if (__mutex_unlock_fast(lock)) | |
521 | return; | |
0d66bf6d | 522 | #endif |
3ca0ff57 | 523 | __mutex_unlock_slowpath(lock, _RET_IP_); |
6053ee3b | 524 | } |
6053ee3b IM |
525 | EXPORT_SYMBOL(mutex_unlock); |
526 | ||
040a0a37 ML |
527 | /** |
528 | * ww_mutex_unlock - release the w/w mutex | |
529 | * @lock: the mutex to be released | |
530 | * | |
531 | * Unlock a mutex that has been locked by this task previously with any of the | |
532 | * ww_mutex_lock* functions (with or without an acquire context). It is | |
533 | * forbidden to release the locks after releasing the acquire context. | |
534 | * | |
535 | * This function must not be used in interrupt context. Unlocking | |
536 | * of a unlocked mutex is not allowed. | |
537 | */ | |
538 | void __sched ww_mutex_unlock(struct ww_mutex *lock) | |
539 | { | |
540 | /* | |
541 | * The unlocking fastpath is the 0->1 transition from 'locked' | |
542 | * into 'unlocked' state: | |
543 | */ | |
544 | if (lock->ctx) { | |
545 | #ifdef CONFIG_DEBUG_MUTEXES | |
546 | DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired); | |
547 | #endif | |
548 | if (lock->ctx->acquired > 0) | |
549 | lock->ctx->acquired--; | |
550 | lock->ctx = NULL; | |
551 | } | |
552 | ||
3ca0ff57 | 553 | mutex_unlock(&lock->base); |
040a0a37 ML |
554 | } |
555 | EXPORT_SYMBOL(ww_mutex_unlock); | |
556 | ||
557 | static inline int __sched | |
63dc47e9 | 558 | __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx) |
040a0a37 ML |
559 | { |
560 | struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); | |
4d3199e4 | 561 | struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx); |
040a0a37 ML |
562 | |
563 | if (!hold_ctx) | |
564 | return 0; | |
565 | ||
040a0a37 ML |
566 | if (ctx->stamp - hold_ctx->stamp <= LONG_MAX && |
567 | (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) { | |
568 | #ifdef CONFIG_DEBUG_MUTEXES | |
569 | DEBUG_LOCKS_WARN_ON(ctx->contending_lock); | |
570 | ctx->contending_lock = ww; | |
571 | #endif | |
572 | return -EDEADLK; | |
573 | } | |
574 | ||
575 | return 0; | |
576 | } | |
577 | ||
6053ee3b IM |
578 | /* |
579 | * Lock a mutex (possibly interruptible), slowpath: | |
580 | */ | |
040a0a37 | 581 | static __always_inline int __sched |
e4564f79 | 582 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
040a0a37 | 583 | struct lockdep_map *nest_lock, unsigned long ip, |
b0267507 | 584 | struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) |
6053ee3b IM |
585 | { |
586 | struct task_struct *task = current; | |
587 | struct mutex_waiter waiter; | |
1fb00c6c | 588 | unsigned long flags; |
9d659ae1 | 589 | bool first = false; |
a40ca565 | 590 | struct ww_mutex *ww; |
040a0a37 | 591 | int ret; |
6053ee3b | 592 | |
0422e83d | 593 | if (use_ww_ctx) { |
a40ca565 | 594 | ww = container_of(lock, struct ww_mutex, base); |
0422e83d CW |
595 | if (unlikely(ww_ctx == READ_ONCE(ww->ctx))) |
596 | return -EALREADY; | |
597 | } | |
598 | ||
41719b03 | 599 | preempt_disable(); |
e4c70a66 | 600 | mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); |
c0226027 | 601 | |
9d659ae1 PZ |
602 | if (__mutex_trylock(lock, false) || |
603 | mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx)) { | |
76916515 | 604 | /* got the lock, yay! */ |
3ca0ff57 | 605 | lock_acquired(&lock->dep_map, ip); |
a40ca565 | 606 | if (use_ww_ctx) |
3ca0ff57 | 607 | ww_mutex_set_context_fastpath(ww, ww_ctx); |
76916515 DB |
608 | preempt_enable(); |
609 | return 0; | |
0d66bf6d | 610 | } |
76916515 | 611 | |
1fb00c6c | 612 | spin_lock_mutex(&lock->wait_lock, flags); |
1e820c96 | 613 | /* |
3ca0ff57 | 614 | * After waiting to acquire the wait_lock, try again. |
1e820c96 | 615 | */ |
9d659ae1 | 616 | if (__mutex_trylock(lock, false)) |
ec83f425 DB |
617 | goto skip_wait; |
618 | ||
9a11b49a | 619 | debug_mutex_lock_common(lock, &waiter); |
6720a305 | 620 | debug_mutex_add_waiter(lock, &waiter, task); |
6053ee3b IM |
621 | |
622 | /* add waiting tasks to the end of the waitqueue (FIFO): */ | |
623 | list_add_tail(&waiter.list, &lock->wait_list); | |
624 | waiter.task = task; | |
625 | ||
9d659ae1 | 626 | if (__mutex_waiter_is_first(lock, &waiter)) |
3ca0ff57 PZ |
627 | __mutex_set_flag(lock, MUTEX_FLAG_WAITERS); |
628 | ||
e4564f79 | 629 | lock_contended(&lock->dep_map, ip); |
4fe87745 | 630 | |
5bbd7e64 | 631 | set_task_state(task, state); |
6053ee3b | 632 | for (;;) { |
5bbd7e64 PZ |
633 | /* |
634 | * Once we hold wait_lock, we're serialized against | |
635 | * mutex_unlock() handing the lock off to us, do a trylock | |
636 | * before testing the error conditions to make sure we pick up | |
637 | * the handoff. | |
638 | */ | |
9d659ae1 | 639 | if (__mutex_trylock(lock, first)) |
5bbd7e64 | 640 | goto acquired; |
6053ee3b IM |
641 | |
642 | /* | |
5bbd7e64 PZ |
643 | * Check for signals and wound conditions while holding |
644 | * wait_lock. This ensures the lock cancellation is ordered | |
645 | * against mutex_unlock() and wake-ups do not go missing. | |
6053ee3b | 646 | */ |
6ad36762 | 647 | if (unlikely(signal_pending_state(state, task))) { |
040a0a37 ML |
648 | ret = -EINTR; |
649 | goto err; | |
650 | } | |
6053ee3b | 651 | |
b0267507 | 652 | if (use_ww_ctx && ww_ctx->acquired > 0) { |
63dc47e9 | 653 | ret = __ww_mutex_lock_check_stamp(lock, ww_ctx); |
040a0a37 ML |
654 | if (ret) |
655 | goto err; | |
6053ee3b | 656 | } |
040a0a37 | 657 | |
1fb00c6c | 658 | spin_unlock_mutex(&lock->wait_lock, flags); |
bd2f5536 | 659 | schedule_preempt_disabled(); |
9d659ae1 PZ |
660 | |
661 | if (!first && __mutex_waiter_is_first(lock, &waiter)) { | |
662 | first = true; | |
663 | __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); | |
664 | } | |
5bbd7e64 PZ |
665 | |
666 | set_task_state(task, state); | |
667 | /* | |
668 | * Here we order against unlock; we must either see it change | |
669 | * state back to RUNNING and fall through the next schedule(), | |
670 | * or we must see its unlock and acquire. | |
671 | */ | |
672 | if (__mutex_trylock(lock, first)) | |
673 | break; | |
674 | ||
675 | spin_lock_mutex(&lock->wait_lock, flags); | |
6053ee3b | 676 | } |
5bbd7e64 PZ |
677 | spin_lock_mutex(&lock->wait_lock, flags); |
678 | acquired: | |
51587bcf DB |
679 | __set_task_state(task, TASK_RUNNING); |
680 | ||
6720a305 | 681 | mutex_remove_waiter(lock, &waiter, task); |
ec83f425 | 682 | if (likely(list_empty(&lock->wait_list))) |
9d659ae1 | 683 | __mutex_clear_flag(lock, MUTEX_FLAGS); |
3ca0ff57 | 684 | |
ec83f425 | 685 | debug_mutex_free_waiter(&waiter); |
6053ee3b | 686 | |
ec83f425 DB |
687 | skip_wait: |
688 | /* got the lock - cleanup and rejoice! */ | |
c7e78cff | 689 | lock_acquired(&lock->dep_map, ip); |
6053ee3b | 690 | |
a40ca565 | 691 | if (use_ww_ctx) |
4bd19084 | 692 | ww_mutex_set_context_slowpath(ww, ww_ctx); |
040a0a37 | 693 | |
1fb00c6c | 694 | spin_unlock_mutex(&lock->wait_lock, flags); |
41719b03 | 695 | preempt_enable(); |
6053ee3b | 696 | return 0; |
040a0a37 ML |
697 | |
698 | err: | |
5bbd7e64 | 699 | __set_task_state(task, TASK_RUNNING); |
6720a305 | 700 | mutex_remove_waiter(lock, &waiter, task); |
040a0a37 ML |
701 | spin_unlock_mutex(&lock->wait_lock, flags); |
702 | debug_mutex_free_waiter(&waiter); | |
703 | mutex_release(&lock->dep_map, 1, ip); | |
704 | preempt_enable(); | |
705 | return ret; | |
6053ee3b IM |
706 | } |
707 | ||
ef5d4707 IM |
708 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
709 | void __sched | |
710 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) | |
711 | { | |
712 | might_sleep(); | |
040a0a37 | 713 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, |
b0267507 | 714 | subclass, NULL, _RET_IP_, NULL, 0); |
ef5d4707 IM |
715 | } |
716 | ||
717 | EXPORT_SYMBOL_GPL(mutex_lock_nested); | |
d63a5a74 | 718 | |
e4c70a66 PZ |
719 | void __sched |
720 | _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest) | |
721 | { | |
722 | might_sleep(); | |
040a0a37 | 723 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, |
b0267507 | 724 | 0, nest, _RET_IP_, NULL, 0); |
e4c70a66 | 725 | } |
e4c70a66 PZ |
726 | EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); |
727 | ||
ad776537 LH |
728 | int __sched |
729 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) | |
730 | { | |
731 | might_sleep(); | |
040a0a37 | 732 | return __mutex_lock_common(lock, TASK_KILLABLE, |
b0267507 | 733 | subclass, NULL, _RET_IP_, NULL, 0); |
ad776537 LH |
734 | } |
735 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); | |
736 | ||
d63a5a74 N |
737 | int __sched |
738 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) | |
739 | { | |
740 | might_sleep(); | |
0d66bf6d | 741 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, |
b0267507 | 742 | subclass, NULL, _RET_IP_, NULL, 0); |
d63a5a74 | 743 | } |
d63a5a74 | 744 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); |
040a0a37 | 745 | |
23010027 DV |
746 | static inline int |
747 | ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) | |
748 | { | |
749 | #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH | |
750 | unsigned tmp; | |
751 | ||
752 | if (ctx->deadlock_inject_countdown-- == 0) { | |
753 | tmp = ctx->deadlock_inject_interval; | |
754 | if (tmp > UINT_MAX/4) | |
755 | tmp = UINT_MAX; | |
756 | else | |
757 | tmp = tmp*2 + tmp + tmp/2; | |
758 | ||
759 | ctx->deadlock_inject_interval = tmp; | |
760 | ctx->deadlock_inject_countdown = tmp; | |
761 | ctx->contending_lock = lock; | |
762 | ||
763 | ww_mutex_unlock(lock); | |
764 | ||
765 | return -EDEADLK; | |
766 | } | |
767 | #endif | |
768 | ||
769 | return 0; | |
770 | } | |
040a0a37 ML |
771 | |
772 | int __sched | |
773 | __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) | |
774 | { | |
23010027 DV |
775 | int ret; |
776 | ||
040a0a37 | 777 | might_sleep(); |
23010027 | 778 | ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, |
b0267507 | 779 | 0, &ctx->dep_map, _RET_IP_, ctx, 1); |
85f48961 | 780 | if (!ret && ctx->acquired > 1) |
23010027 DV |
781 | return ww_mutex_deadlock_injection(lock, ctx); |
782 | ||
783 | return ret; | |
040a0a37 ML |
784 | } |
785 | EXPORT_SYMBOL_GPL(__ww_mutex_lock); | |
786 | ||
787 | int __sched | |
788 | __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) | |
789 | { | |
23010027 DV |
790 | int ret; |
791 | ||
040a0a37 | 792 | might_sleep(); |
23010027 | 793 | ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, |
b0267507 | 794 | 0, &ctx->dep_map, _RET_IP_, ctx, 1); |
23010027 | 795 | |
85f48961 | 796 | if (!ret && ctx->acquired > 1) |
23010027 DV |
797 | return ww_mutex_deadlock_injection(lock, ctx); |
798 | ||
799 | return ret; | |
040a0a37 ML |
800 | } |
801 | EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible); | |
802 | ||
ef5d4707 IM |
803 | #endif |
804 | ||
6053ee3b IM |
805 | /* |
806 | * Release the lock, slowpath: | |
807 | */ | |
3ca0ff57 | 808 | static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip) |
6053ee3b | 809 | { |
9d659ae1 | 810 | struct task_struct *next = NULL; |
3ca0ff57 | 811 | unsigned long owner, flags; |
1329ce6f | 812 | WAKE_Q(wake_q); |
6053ee3b | 813 | |
3ca0ff57 PZ |
814 | mutex_release(&lock->dep_map, 1, ip); |
815 | ||
6053ee3b | 816 | /* |
9d659ae1 PZ |
817 | * Release the lock before (potentially) taking the spinlock such that |
818 | * other contenders can get on with things ASAP. | |
819 | * | |
820 | * Except when HANDOFF, in that case we must not clear the owner field, | |
821 | * but instead set it to the top waiter. | |
6053ee3b | 822 | */ |
9d659ae1 PZ |
823 | owner = atomic_long_read(&lock->owner); |
824 | for (;;) { | |
825 | unsigned long old; | |
826 | ||
827 | #ifdef CONFIG_DEBUG_MUTEXES | |
828 | DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current); | |
829 | #endif | |
830 | ||
831 | if (owner & MUTEX_FLAG_HANDOFF) | |
832 | break; | |
833 | ||
834 | old = atomic_long_cmpxchg_release(&lock->owner, owner, | |
835 | __owner_flags(owner)); | |
836 | if (old == owner) { | |
837 | if (owner & MUTEX_FLAG_WAITERS) | |
838 | break; | |
839 | ||
840 | return; | |
841 | } | |
842 | ||
843 | owner = old; | |
844 | } | |
6053ee3b | 845 | |
1d8fe7dc | 846 | spin_lock_mutex(&lock->wait_lock, flags); |
1d8fe7dc | 847 | debug_mutex_unlock(lock); |
6053ee3b IM |
848 | if (!list_empty(&lock->wait_list)) { |
849 | /* get the first entry from the wait-list: */ | |
850 | struct mutex_waiter *waiter = | |
9d659ae1 PZ |
851 | list_first_entry(&lock->wait_list, |
852 | struct mutex_waiter, list); | |
853 | ||
854 | next = waiter->task; | |
6053ee3b IM |
855 | |
856 | debug_mutex_wake_waiter(lock, waiter); | |
9d659ae1 | 857 | wake_q_add(&wake_q, next); |
6053ee3b IM |
858 | } |
859 | ||
9d659ae1 PZ |
860 | if (owner & MUTEX_FLAG_HANDOFF) |
861 | __mutex_handoff(lock, next); | |
862 | ||
1fb00c6c | 863 | spin_unlock_mutex(&lock->wait_lock, flags); |
9d659ae1 | 864 | |
1329ce6f | 865 | wake_up_q(&wake_q); |
6053ee3b IM |
866 | } |
867 | ||
e4564f79 | 868 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
869 | /* |
870 | * Here come the less common (and hence less performance-critical) APIs: | |
871 | * mutex_lock_interruptible() and mutex_trylock(). | |
872 | */ | |
7ad5b3a5 | 873 | static noinline int __sched |
a41b56ef | 874 | __mutex_lock_killable_slowpath(struct mutex *lock); |
ad776537 | 875 | |
7ad5b3a5 | 876 | static noinline int __sched |
a41b56ef | 877 | __mutex_lock_interruptible_slowpath(struct mutex *lock); |
6053ee3b | 878 | |
ef5dc121 RD |
879 | /** |
880 | * mutex_lock_interruptible - acquire the mutex, interruptible | |
6053ee3b IM |
881 | * @lock: the mutex to be acquired |
882 | * | |
883 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has | |
884 | * been acquired or sleep until the mutex becomes available. If a | |
885 | * signal arrives while waiting for the lock then this function | |
886 | * returns -EINTR. | |
887 | * | |
888 | * This function is similar to (but not equivalent to) down_interruptible(). | |
889 | */ | |
7ad5b3a5 | 890 | int __sched mutex_lock_interruptible(struct mutex *lock) |
6053ee3b | 891 | { |
c544bdb1 | 892 | might_sleep(); |
3ca0ff57 PZ |
893 | |
894 | if (__mutex_trylock_fast(lock)) | |
a41b56ef | 895 | return 0; |
3ca0ff57 PZ |
896 | |
897 | return __mutex_lock_interruptible_slowpath(lock); | |
6053ee3b IM |
898 | } |
899 | ||
900 | EXPORT_SYMBOL(mutex_lock_interruptible); | |
901 | ||
7ad5b3a5 | 902 | int __sched mutex_lock_killable(struct mutex *lock) |
ad776537 LH |
903 | { |
904 | might_sleep(); | |
3ca0ff57 PZ |
905 | |
906 | if (__mutex_trylock_fast(lock)) | |
a41b56ef | 907 | return 0; |
3ca0ff57 PZ |
908 | |
909 | return __mutex_lock_killable_slowpath(lock); | |
ad776537 LH |
910 | } |
911 | EXPORT_SYMBOL(mutex_lock_killable); | |
912 | ||
3ca0ff57 PZ |
913 | static noinline void __sched |
914 | __mutex_lock_slowpath(struct mutex *lock) | |
e4564f79 | 915 | { |
040a0a37 | 916 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, |
b0267507 | 917 | NULL, _RET_IP_, NULL, 0); |
e4564f79 PZ |
918 | } |
919 | ||
7ad5b3a5 | 920 | static noinline int __sched |
a41b56ef | 921 | __mutex_lock_killable_slowpath(struct mutex *lock) |
ad776537 | 922 | { |
040a0a37 | 923 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, |
b0267507 | 924 | NULL, _RET_IP_, NULL, 0); |
ad776537 LH |
925 | } |
926 | ||
7ad5b3a5 | 927 | static noinline int __sched |
a41b56ef | 928 | __mutex_lock_interruptible_slowpath(struct mutex *lock) |
6053ee3b | 929 | { |
040a0a37 | 930 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, |
b0267507 | 931 | NULL, _RET_IP_, NULL, 0); |
040a0a37 ML |
932 | } |
933 | ||
934 | static noinline int __sched | |
935 | __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) | |
936 | { | |
937 | return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0, | |
b0267507 | 938 | NULL, _RET_IP_, ctx, 1); |
6053ee3b | 939 | } |
040a0a37 ML |
940 | |
941 | static noinline int __sched | |
942 | __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock, | |
943 | struct ww_acquire_ctx *ctx) | |
944 | { | |
945 | return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0, | |
b0267507 | 946 | NULL, _RET_IP_, ctx, 1); |
040a0a37 ML |
947 | } |
948 | ||
e4564f79 | 949 | #endif |
6053ee3b | 950 | |
ef5dc121 RD |
951 | /** |
952 | * mutex_trylock - try to acquire the mutex, without waiting | |
6053ee3b IM |
953 | * @lock: the mutex to be acquired |
954 | * | |
955 | * Try to acquire the mutex atomically. Returns 1 if the mutex | |
956 | * has been acquired successfully, and 0 on contention. | |
957 | * | |
958 | * NOTE: this function follows the spin_trylock() convention, so | |
ef5dc121 | 959 | * it is negated from the down_trylock() return values! Be careful |
6053ee3b IM |
960 | * about this when converting semaphore users to mutexes. |
961 | * | |
962 | * This function must not be used in interrupt context. The | |
963 | * mutex must be released by the same task that acquired it. | |
964 | */ | |
7ad5b3a5 | 965 | int __sched mutex_trylock(struct mutex *lock) |
6053ee3b | 966 | { |
9d659ae1 | 967 | bool locked = __mutex_trylock(lock, false); |
0d66bf6d | 968 | |
3ca0ff57 PZ |
969 | if (locked) |
970 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); | |
0d66bf6d | 971 | |
3ca0ff57 | 972 | return locked; |
6053ee3b | 973 | } |
6053ee3b | 974 | EXPORT_SYMBOL(mutex_trylock); |
a511e3f9 | 975 | |
040a0a37 ML |
976 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
977 | int __sched | |
978 | __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) | |
979 | { | |
040a0a37 ML |
980 | might_sleep(); |
981 | ||
3ca0ff57 | 982 | if (__mutex_trylock_fast(&lock->base)) { |
040a0a37 | 983 | ww_mutex_set_context_fastpath(lock, ctx); |
3ca0ff57 PZ |
984 | return 0; |
985 | } | |
986 | ||
987 | return __ww_mutex_lock_slowpath(lock, ctx); | |
040a0a37 ML |
988 | } |
989 | EXPORT_SYMBOL(__ww_mutex_lock); | |
990 | ||
991 | int __sched | |
992 | __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) | |
993 | { | |
040a0a37 ML |
994 | might_sleep(); |
995 | ||
3ca0ff57 | 996 | if (__mutex_trylock_fast(&lock->base)) { |
040a0a37 | 997 | ww_mutex_set_context_fastpath(lock, ctx); |
3ca0ff57 PZ |
998 | return 0; |
999 | } | |
1000 | ||
1001 | return __ww_mutex_lock_interruptible_slowpath(lock, ctx); | |
040a0a37 ML |
1002 | } |
1003 | EXPORT_SYMBOL(__ww_mutex_lock_interruptible); | |
1004 | ||
1005 | #endif | |
1006 | ||
a511e3f9 AM |
1007 | /** |
1008 | * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 | |
1009 | * @cnt: the atomic which we are to dec | |
1010 | * @lock: the mutex to return holding if we dec to 0 | |
1011 | * | |
1012 | * return true and hold lock if we dec to 0, return false otherwise | |
1013 | */ | |
1014 | int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) | |
1015 | { | |
1016 | /* dec if we can't possibly hit 0 */ | |
1017 | if (atomic_add_unless(cnt, -1, 1)) | |
1018 | return 0; | |
1019 | /* we might hit 0, so take the lock */ | |
1020 | mutex_lock(lock); | |
1021 | if (!atomic_dec_and_test(cnt)) { | |
1022 | /* when we actually did the dec, we didn't hit 0 */ | |
1023 | mutex_unlock(lock); | |
1024 | return 0; | |
1025 | } | |
1026 | /* we hit 0, and we hold the lock */ | |
1027 | return 1; | |
1028 | } | |
1029 | EXPORT_SYMBOL(atomic_dec_and_mutex_lock); |