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Commit | Line | Data |
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6053ee3b IM |
1 | /* |
2 | * kernel/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 | * | |
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 | * | |
6053ee3b IM |
18 | * Also see Documentation/mutex-design.txt. |
19 | */ | |
20 | #include <linux/mutex.h> | |
21 | #include <linux/sched.h> | |
8bd75c77 | 22 | #include <linux/sched/rt.h> |
9984de1a | 23 | #include <linux/export.h> |
6053ee3b IM |
24 | #include <linux/spinlock.h> |
25 | #include <linux/interrupt.h> | |
9a11b49a | 26 | #include <linux/debug_locks.h> |
6053ee3b IM |
27 | |
28 | /* | |
29 | * In the DEBUG case we are using the "NULL fastpath" for mutexes, | |
30 | * which forces all calls into the slowpath: | |
31 | */ | |
32 | #ifdef CONFIG_DEBUG_MUTEXES | |
33 | # include "mutex-debug.h" | |
34 | # include <asm-generic/mutex-null.h> | |
35 | #else | |
36 | # include "mutex.h" | |
37 | # include <asm/mutex.h> | |
38 | #endif | |
39 | ||
0dc8c730 WL |
40 | /* |
41 | * A mutex count of -1 indicates that waiters are sleeping waiting for the | |
42 | * mutex. Some architectures can allow any negative number, not just -1, for | |
43 | * this purpose. | |
44 | */ | |
45 | #ifdef __ARCH_ALLOW_ANY_NEGATIVE_MUTEX_COUNT | |
46 | #define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) >= 0) | |
47 | #else | |
48 | #define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) != -1) | |
49 | #endif | |
50 | ||
ef5d4707 IM |
51 | void |
52 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) | |
6053ee3b IM |
53 | { |
54 | atomic_set(&lock->count, 1); | |
55 | spin_lock_init(&lock->wait_lock); | |
56 | INIT_LIST_HEAD(&lock->wait_list); | |
0d66bf6d | 57 | mutex_clear_owner(lock); |
6053ee3b | 58 | |
ef5d4707 | 59 | debug_mutex_init(lock, name, key); |
6053ee3b IM |
60 | } |
61 | ||
62 | EXPORT_SYMBOL(__mutex_init); | |
63 | ||
e4564f79 | 64 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
65 | /* |
66 | * We split the mutex lock/unlock logic into separate fastpath and | |
67 | * slowpath functions, to reduce the register pressure on the fastpath. | |
68 | * We also put the fastpath first in the kernel image, to make sure the | |
69 | * branch is predicted by the CPU as default-untaken. | |
70 | */ | |
7918baa5 | 71 | static __used noinline void __sched |
9a11b49a | 72 | __mutex_lock_slowpath(atomic_t *lock_count); |
6053ee3b | 73 | |
ef5dc121 | 74 | /** |
6053ee3b IM |
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 mutex 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 | */ | |
b09d2501 | 95 | void __sched mutex_lock(struct mutex *lock) |
6053ee3b | 96 | { |
c544bdb1 | 97 | might_sleep(); |
6053ee3b IM |
98 | /* |
99 | * The locking fastpath is the 1->0 transition from | |
100 | * 'unlocked' into 'locked' state. | |
6053ee3b IM |
101 | */ |
102 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); | |
0d66bf6d | 103 | mutex_set_owner(lock); |
6053ee3b IM |
104 | } |
105 | ||
106 | EXPORT_SYMBOL(mutex_lock); | |
e4564f79 | 107 | #endif |
6053ee3b | 108 | |
41fcb9f2 WL |
109 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
110 | /* | |
111 | * Mutex spinning code migrated from kernel/sched/core.c | |
112 | */ | |
113 | ||
114 | static inline bool owner_running(struct mutex *lock, struct task_struct *owner) | |
115 | { | |
116 | if (lock->owner != owner) | |
117 | return false; | |
118 | ||
119 | /* | |
120 | * Ensure we emit the owner->on_cpu, dereference _after_ checking | |
121 | * lock->owner still matches owner, if that fails, owner might | |
122 | * point to free()d memory, if it still matches, the rcu_read_lock() | |
123 | * ensures the memory stays valid. | |
124 | */ | |
125 | barrier(); | |
126 | ||
127 | return owner->on_cpu; | |
128 | } | |
129 | ||
130 | /* | |
131 | * Look out! "owner" is an entirely speculative pointer | |
132 | * access and not reliable. | |
133 | */ | |
134 | static noinline | |
135 | int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) | |
136 | { | |
137 | rcu_read_lock(); | |
138 | while (owner_running(lock, owner)) { | |
139 | if (need_resched()) | |
140 | break; | |
141 | ||
142 | arch_mutex_cpu_relax(); | |
143 | } | |
144 | rcu_read_unlock(); | |
145 | ||
146 | /* | |
147 | * We break out the loop above on need_resched() and when the | |
148 | * owner changed, which is a sign for heavy contention. Return | |
149 | * success only when lock->owner is NULL. | |
150 | */ | |
151 | return lock->owner == NULL; | |
152 | } | |
153 | #endif | |
154 | ||
7918baa5 | 155 | static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); |
6053ee3b | 156 | |
ef5dc121 | 157 | /** |
6053ee3b IM |
158 | * mutex_unlock - release the mutex |
159 | * @lock: the mutex to be released | |
160 | * | |
161 | * Unlock a mutex that has been locked by this task previously. | |
162 | * | |
163 | * This function must not be used in interrupt context. Unlocking | |
164 | * of a not locked mutex is not allowed. | |
165 | * | |
166 | * This function is similar to (but not equivalent to) up(). | |
167 | */ | |
7ad5b3a5 | 168 | void __sched mutex_unlock(struct mutex *lock) |
6053ee3b IM |
169 | { |
170 | /* | |
171 | * The unlocking fastpath is the 0->1 transition from 'locked' | |
172 | * into 'unlocked' state: | |
6053ee3b | 173 | */ |
0d66bf6d PZ |
174 | #ifndef CONFIG_DEBUG_MUTEXES |
175 | /* | |
176 | * When debugging is enabled we must not clear the owner before time, | |
177 | * the slow path will always be taken, and that clears the owner field | |
178 | * after verifying that it was indeed current. | |
179 | */ | |
180 | mutex_clear_owner(lock); | |
181 | #endif | |
6053ee3b IM |
182 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); |
183 | } | |
184 | ||
185 | EXPORT_SYMBOL(mutex_unlock); | |
186 | ||
187 | /* | |
188 | * Lock a mutex (possibly interruptible), slowpath: | |
189 | */ | |
190 | static inline int __sched | |
e4564f79 | 191 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
e4c70a66 | 192 | struct lockdep_map *nest_lock, unsigned long ip) |
6053ee3b IM |
193 | { |
194 | struct task_struct *task = current; | |
195 | struct mutex_waiter waiter; | |
1fb00c6c | 196 | unsigned long flags; |
6053ee3b | 197 | |
41719b03 | 198 | preempt_disable(); |
e4c70a66 | 199 | mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); |
c0226027 FW |
200 | |
201 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER | |
0d66bf6d PZ |
202 | /* |
203 | * Optimistic spinning. | |
204 | * | |
205 | * We try to spin for acquisition when we find that there are no | |
206 | * pending waiters and the lock owner is currently running on a | |
207 | * (different) CPU. | |
208 | * | |
209 | * The rationale is that if the lock owner is running, it is likely to | |
210 | * release the lock soon. | |
211 | * | |
212 | * Since this needs the lock owner, and this mutex implementation | |
213 | * doesn't track the owner atomically in the lock field, we need to | |
214 | * track it non-atomically. | |
215 | * | |
216 | * We can't do this for DEBUG_MUTEXES because that relies on wait_lock | |
217 | * to serialize everything. | |
218 | */ | |
219 | ||
220 | for (;;) { | |
c6eb3dda | 221 | struct task_struct *owner; |
0d66bf6d | 222 | |
0d66bf6d PZ |
223 | /* |
224 | * If there's an owner, wait for it to either | |
225 | * release the lock or go to sleep. | |
226 | */ | |
227 | owner = ACCESS_ONCE(lock->owner); | |
228 | if (owner && !mutex_spin_on_owner(lock, owner)) | |
229 | break; | |
230 | ||
0dc8c730 WL |
231 | if ((atomic_read(&lock->count) == 1) && |
232 | (atomic_cmpxchg(&lock->count, 1, 0) == 1)) { | |
ac6e60ee CM |
233 | lock_acquired(&lock->dep_map, ip); |
234 | mutex_set_owner(lock); | |
235 | preempt_enable(); | |
236 | return 0; | |
237 | } | |
238 | ||
0d66bf6d PZ |
239 | /* |
240 | * When there's no owner, we might have preempted between the | |
241 | * owner acquiring the lock and setting the owner field. If | |
242 | * we're an RT task that will live-lock because we won't let | |
243 | * the owner complete. | |
244 | */ | |
245 | if (!owner && (need_resched() || rt_task(task))) | |
246 | break; | |
247 | ||
0d66bf6d PZ |
248 | /* |
249 | * The cpu_relax() call is a compiler barrier which forces | |
250 | * everything in this loop to be re-loaded. We don't need | |
251 | * memory barriers as we'll eventually observe the right | |
252 | * values at the cost of a few extra spins. | |
253 | */ | |
335d7afb | 254 | arch_mutex_cpu_relax(); |
0d66bf6d PZ |
255 | } |
256 | #endif | |
1fb00c6c | 257 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b | 258 | |
9a11b49a | 259 | debug_mutex_lock_common(lock, &waiter); |
c9f4f06d | 260 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
6053ee3b IM |
261 | |
262 | /* add waiting tasks to the end of the waitqueue (FIFO): */ | |
263 | list_add_tail(&waiter.list, &lock->wait_list); | |
264 | waiter.task = task; | |
265 | ||
0dc8c730 | 266 | if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, -1) == 1)) |
4fe87745 PZ |
267 | goto done; |
268 | ||
e4564f79 | 269 | lock_contended(&lock->dep_map, ip); |
4fe87745 | 270 | |
6053ee3b IM |
271 | for (;;) { |
272 | /* | |
273 | * Lets try to take the lock again - this is needed even if | |
274 | * we get here for the first time (shortly after failing to | |
275 | * acquire the lock), to make sure that we get a wakeup once | |
276 | * it's unlocked. Later on, if we sleep, this is the | |
277 | * operation that gives us the lock. We xchg it to -1, so | |
278 | * that when we release the lock, we properly wake up the | |
279 | * other waiters: | |
280 | */ | |
0dc8c730 WL |
281 | if (MUTEX_SHOW_NO_WAITER(lock) && |
282 | (atomic_xchg(&lock->count, -1) == 1)) | |
6053ee3b IM |
283 | break; |
284 | ||
285 | /* | |
286 | * got a signal? (This code gets eliminated in the | |
287 | * TASK_UNINTERRUPTIBLE case.) | |
288 | */ | |
6ad36762 | 289 | if (unlikely(signal_pending_state(state, task))) { |
ad776537 LH |
290 | mutex_remove_waiter(lock, &waiter, |
291 | task_thread_info(task)); | |
e4564f79 | 292 | mutex_release(&lock->dep_map, 1, ip); |
1fb00c6c | 293 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
294 | |
295 | debug_mutex_free_waiter(&waiter); | |
41719b03 | 296 | preempt_enable(); |
6053ee3b IM |
297 | return -EINTR; |
298 | } | |
299 | __set_task_state(task, state); | |
300 | ||
25985edc | 301 | /* didn't get the lock, go to sleep: */ |
1fb00c6c | 302 | spin_unlock_mutex(&lock->wait_lock, flags); |
bd2f5536 | 303 | schedule_preempt_disabled(); |
1fb00c6c | 304 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
305 | } |
306 | ||
4fe87745 | 307 | done: |
c7e78cff | 308 | lock_acquired(&lock->dep_map, ip); |
6053ee3b | 309 | /* got the lock - rejoice! */ |
0d66bf6d PZ |
310 | mutex_remove_waiter(lock, &waiter, current_thread_info()); |
311 | mutex_set_owner(lock); | |
6053ee3b IM |
312 | |
313 | /* set it to 0 if there are no waiters left: */ | |
314 | if (likely(list_empty(&lock->wait_list))) | |
315 | atomic_set(&lock->count, 0); | |
316 | ||
1fb00c6c | 317 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
318 | |
319 | debug_mutex_free_waiter(&waiter); | |
41719b03 | 320 | preempt_enable(); |
6053ee3b | 321 | |
6053ee3b IM |
322 | return 0; |
323 | } | |
324 | ||
ef5d4707 IM |
325 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
326 | void __sched | |
327 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) | |
328 | { | |
329 | might_sleep(); | |
e4c70a66 | 330 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_); |
ef5d4707 IM |
331 | } |
332 | ||
333 | EXPORT_SYMBOL_GPL(mutex_lock_nested); | |
d63a5a74 | 334 | |
e4c70a66 PZ |
335 | void __sched |
336 | _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest) | |
337 | { | |
338 | might_sleep(); | |
339 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_); | |
340 | } | |
341 | ||
342 | EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); | |
343 | ||
ad776537 LH |
344 | int __sched |
345 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) | |
346 | { | |
347 | might_sleep(); | |
e4c70a66 | 348 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_); |
ad776537 LH |
349 | } |
350 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); | |
351 | ||
d63a5a74 N |
352 | int __sched |
353 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) | |
354 | { | |
355 | might_sleep(); | |
0d66bf6d | 356 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, |
e4c70a66 | 357 | subclass, NULL, _RET_IP_); |
d63a5a74 N |
358 | } |
359 | ||
360 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); | |
ef5d4707 IM |
361 | #endif |
362 | ||
6053ee3b IM |
363 | /* |
364 | * Release the lock, slowpath: | |
365 | */ | |
7ad5b3a5 | 366 | static inline void |
ef5d4707 | 367 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) |
6053ee3b | 368 | { |
02706647 | 369 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
1fb00c6c | 370 | unsigned long flags; |
6053ee3b | 371 | |
1fb00c6c | 372 | spin_lock_mutex(&lock->wait_lock, flags); |
ef5d4707 | 373 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
9a11b49a | 374 | debug_mutex_unlock(lock); |
6053ee3b IM |
375 | |
376 | /* | |
377 | * some architectures leave the lock unlocked in the fastpath failure | |
378 | * case, others need to leave it locked. In the later case we have to | |
379 | * unlock it here | |
380 | */ | |
381 | if (__mutex_slowpath_needs_to_unlock()) | |
382 | atomic_set(&lock->count, 1); | |
383 | ||
6053ee3b IM |
384 | if (!list_empty(&lock->wait_list)) { |
385 | /* get the first entry from the wait-list: */ | |
386 | struct mutex_waiter *waiter = | |
387 | list_entry(lock->wait_list.next, | |
388 | struct mutex_waiter, list); | |
389 | ||
390 | debug_mutex_wake_waiter(lock, waiter); | |
391 | ||
392 | wake_up_process(waiter->task); | |
393 | } | |
394 | ||
1fb00c6c | 395 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
396 | } |
397 | ||
9a11b49a IM |
398 | /* |
399 | * Release the lock, slowpath: | |
400 | */ | |
7918baa5 | 401 | static __used noinline void |
9a11b49a IM |
402 | __mutex_unlock_slowpath(atomic_t *lock_count) |
403 | { | |
ef5d4707 | 404 | __mutex_unlock_common_slowpath(lock_count, 1); |
9a11b49a IM |
405 | } |
406 | ||
e4564f79 | 407 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
408 | /* |
409 | * Here come the less common (and hence less performance-critical) APIs: | |
410 | * mutex_lock_interruptible() and mutex_trylock(). | |
411 | */ | |
7ad5b3a5 | 412 | static noinline int __sched |
ad776537 LH |
413 | __mutex_lock_killable_slowpath(atomic_t *lock_count); |
414 | ||
7ad5b3a5 | 415 | static noinline int __sched |
9a11b49a | 416 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
6053ee3b | 417 | |
ef5dc121 RD |
418 | /** |
419 | * mutex_lock_interruptible - acquire the mutex, interruptible | |
6053ee3b IM |
420 | * @lock: the mutex to be acquired |
421 | * | |
422 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has | |
423 | * been acquired or sleep until the mutex becomes available. If a | |
424 | * signal arrives while waiting for the lock then this function | |
425 | * returns -EINTR. | |
426 | * | |
427 | * This function is similar to (but not equivalent to) down_interruptible(). | |
428 | */ | |
7ad5b3a5 | 429 | int __sched mutex_lock_interruptible(struct mutex *lock) |
6053ee3b | 430 | { |
0d66bf6d PZ |
431 | int ret; |
432 | ||
c544bdb1 | 433 | might_sleep(); |
0d66bf6d | 434 | ret = __mutex_fastpath_lock_retval |
6053ee3b | 435 | (&lock->count, __mutex_lock_interruptible_slowpath); |
0d66bf6d PZ |
436 | if (!ret) |
437 | mutex_set_owner(lock); | |
438 | ||
439 | return ret; | |
6053ee3b IM |
440 | } |
441 | ||
442 | EXPORT_SYMBOL(mutex_lock_interruptible); | |
443 | ||
7ad5b3a5 | 444 | int __sched mutex_lock_killable(struct mutex *lock) |
ad776537 | 445 | { |
0d66bf6d PZ |
446 | int ret; |
447 | ||
ad776537 | 448 | might_sleep(); |
0d66bf6d | 449 | ret = __mutex_fastpath_lock_retval |
ad776537 | 450 | (&lock->count, __mutex_lock_killable_slowpath); |
0d66bf6d PZ |
451 | if (!ret) |
452 | mutex_set_owner(lock); | |
453 | ||
454 | return ret; | |
ad776537 LH |
455 | } |
456 | EXPORT_SYMBOL(mutex_lock_killable); | |
457 | ||
7918baa5 | 458 | static __used noinline void __sched |
e4564f79 PZ |
459 | __mutex_lock_slowpath(atomic_t *lock_count) |
460 | { | |
461 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
462 | ||
e4c70a66 | 463 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_); |
e4564f79 PZ |
464 | } |
465 | ||
7ad5b3a5 | 466 | static noinline int __sched |
ad776537 LH |
467 | __mutex_lock_killable_slowpath(atomic_t *lock_count) |
468 | { | |
469 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
470 | ||
e4c70a66 | 471 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, NULL, _RET_IP_); |
ad776537 LH |
472 | } |
473 | ||
7ad5b3a5 | 474 | static noinline int __sched |
9a11b49a | 475 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
6053ee3b IM |
476 | { |
477 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
478 | ||
e4c70a66 | 479 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_); |
6053ee3b | 480 | } |
e4564f79 | 481 | #endif |
6053ee3b IM |
482 | |
483 | /* | |
484 | * Spinlock based trylock, we take the spinlock and check whether we | |
485 | * can get the lock: | |
486 | */ | |
487 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) | |
488 | { | |
489 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
1fb00c6c | 490 | unsigned long flags; |
6053ee3b IM |
491 | int prev; |
492 | ||
1fb00c6c | 493 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
494 | |
495 | prev = atomic_xchg(&lock->count, -1); | |
ef5d4707 | 496 | if (likely(prev == 1)) { |
0d66bf6d | 497 | mutex_set_owner(lock); |
ef5d4707 IM |
498 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
499 | } | |
0d66bf6d | 500 | |
6053ee3b IM |
501 | /* Set it back to 0 if there are no waiters: */ |
502 | if (likely(list_empty(&lock->wait_list))) | |
503 | atomic_set(&lock->count, 0); | |
504 | ||
1fb00c6c | 505 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
506 | |
507 | return prev == 1; | |
508 | } | |
509 | ||
ef5dc121 RD |
510 | /** |
511 | * mutex_trylock - try to acquire the mutex, without waiting | |
6053ee3b IM |
512 | * @lock: the mutex to be acquired |
513 | * | |
514 | * Try to acquire the mutex atomically. Returns 1 if the mutex | |
515 | * has been acquired successfully, and 0 on contention. | |
516 | * | |
517 | * NOTE: this function follows the spin_trylock() convention, so | |
ef5dc121 | 518 | * it is negated from the down_trylock() return values! Be careful |
6053ee3b IM |
519 | * about this when converting semaphore users to mutexes. |
520 | * | |
521 | * This function must not be used in interrupt context. The | |
522 | * mutex must be released by the same task that acquired it. | |
523 | */ | |
7ad5b3a5 | 524 | int __sched mutex_trylock(struct mutex *lock) |
6053ee3b | 525 | { |
0d66bf6d PZ |
526 | int ret; |
527 | ||
528 | ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); | |
529 | if (ret) | |
530 | mutex_set_owner(lock); | |
531 | ||
532 | return ret; | |
6053ee3b | 533 | } |
6053ee3b | 534 | EXPORT_SYMBOL(mutex_trylock); |
a511e3f9 AM |
535 | |
536 | /** | |
537 | * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 | |
538 | * @cnt: the atomic which we are to dec | |
539 | * @lock: the mutex to return holding if we dec to 0 | |
540 | * | |
541 | * return true and hold lock if we dec to 0, return false otherwise | |
542 | */ | |
543 | int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) | |
544 | { | |
545 | /* dec if we can't possibly hit 0 */ | |
546 | if (atomic_add_unless(cnt, -1, 1)) | |
547 | return 0; | |
548 | /* we might hit 0, so take the lock */ | |
549 | mutex_lock(lock); | |
550 | if (!atomic_dec_and_test(cnt)) { | |
551 | /* when we actually did the dec, we didn't hit 0 */ | |
552 | mutex_unlock(lock); | |
553 | return 0; | |
554 | } | |
555 | /* we hit 0, and we hold the lock */ | |
556 | return 1; | |
557 | } | |
558 | EXPORT_SYMBOL(atomic_dec_and_mutex_lock); |