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Source at commit b13e7eb172b6f08e5fc22da162bdde5fcde201b5 created 11 years 11 months ago. By Maarten ter Huurne, fbcon: Add 6x10 font | |
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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 | * |
13 | * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline |
14 | * from the -rt tree, where it was originally implemented for rtmutexes |
15 | * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale |
16 | * and Sven Dietrich. |
17 | * |
18 | * Also see Documentation/mutex-design.txt. |
19 | */ |
20 | #include <linux/mutex.h> |
21 | #include <linux/sched.h> |
22 | #include <linux/export.h> |
23 | #include <linux/spinlock.h> |
24 | #include <linux/interrupt.h> |
25 | #include <linux/debug_locks.h> |
26 | |
27 | /* |
28 | * In the DEBUG case we are using the "NULL fastpath" for mutexes, |
29 | * which forces all calls into the slowpath: |
30 | */ |
31 | #ifdef CONFIG_DEBUG_MUTEXES |
32 | # include "mutex-debug.h" |
33 | # include <asm-generic/mutex-null.h> |
34 | #else |
35 | # include "mutex.h" |
36 | # include <asm/mutex.h> |
37 | #endif |
38 | |
39 | void |
40 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) |
41 | { |
42 | atomic_set(&lock->count, 1); |
43 | spin_lock_init(&lock->wait_lock); |
44 | INIT_LIST_HEAD(&lock->wait_list); |
45 | mutex_clear_owner(lock); |
46 | |
47 | debug_mutex_init(lock, name, key); |
48 | } |
49 | |
50 | EXPORT_SYMBOL(__mutex_init); |
51 | |
52 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
53 | /* |
54 | * We split the mutex lock/unlock logic into separate fastpath and |
55 | * slowpath functions, to reduce the register pressure on the fastpath. |
56 | * We also put the fastpath first in the kernel image, to make sure the |
57 | * branch is predicted by the CPU as default-untaken. |
58 | */ |
59 | static __used noinline void __sched |
60 | __mutex_lock_slowpath(atomic_t *lock_count); |
61 | |
62 | /** |
63 | * mutex_lock - acquire the mutex |
64 | * @lock: the mutex to be acquired |
65 | * |
66 | * Lock the mutex exclusively for this task. If the mutex is not |
67 | * available right now, it will sleep until it can get it. |
68 | * |
69 | * The mutex must later on be released by the same task that |
70 | * acquired it. Recursive locking is not allowed. The task |
71 | * may not exit without first unlocking the mutex. Also, kernel |
72 | * memory where the mutex resides mutex must not be freed with |
73 | * the mutex still locked. The mutex must first be initialized |
74 | * (or statically defined) before it can be locked. memset()-ing |
75 | * the mutex to 0 is not allowed. |
76 | * |
77 | * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging |
78 | * checks that will enforce the restrictions and will also do |
79 | * deadlock debugging. ) |
80 | * |
81 | * This function is similar to (but not equivalent to) down(). |
82 | */ |
83 | void __sched mutex_lock(struct mutex *lock) |
84 | { |
85 | might_sleep(); |
86 | /* |
87 | * The locking fastpath is the 1->0 transition from |
88 | * 'unlocked' into 'locked' state. |
89 | */ |
90 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); |
91 | mutex_set_owner(lock); |
92 | } |
93 | |
94 | EXPORT_SYMBOL(mutex_lock); |
95 | #endif |
96 | |
97 | static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); |
98 | |
99 | /** |
100 | * mutex_unlock - release the mutex |
101 | * @lock: the mutex to be released |
102 | * |
103 | * Unlock a mutex that has been locked by this task previously. |
104 | * |
105 | * This function must not be used in interrupt context. Unlocking |
106 | * of a not locked mutex is not allowed. |
107 | * |
108 | * This function is similar to (but not equivalent to) up(). |
109 | */ |
110 | void __sched mutex_unlock(struct mutex *lock) |
111 | { |
112 | /* |
113 | * The unlocking fastpath is the 0->1 transition from 'locked' |
114 | * into 'unlocked' state: |
115 | */ |
116 | #ifndef CONFIG_DEBUG_MUTEXES |
117 | /* |
118 | * When debugging is enabled we must not clear the owner before time, |
119 | * the slow path will always be taken, and that clears the owner field |
120 | * after verifying that it was indeed current. |
121 | */ |
122 | mutex_clear_owner(lock); |
123 | #endif |
124 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); |
125 | } |
126 | |
127 | EXPORT_SYMBOL(mutex_unlock); |
128 | |
129 | /* |
130 | * Lock a mutex (possibly interruptible), slowpath: |
131 | */ |
132 | static inline int __sched |
133 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
134 | struct lockdep_map *nest_lock, unsigned long ip) |
135 | { |
136 | struct task_struct *task = current; |
137 | struct mutex_waiter waiter; |
138 | unsigned long flags; |
139 | |
140 | preempt_disable(); |
141 | mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); |
142 | |
143 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
144 | /* |
145 | * Optimistic spinning. |
146 | * |
147 | * We try to spin for acquisition when we find that there are no |
148 | * pending waiters and the lock owner is currently running on a |
149 | * (different) CPU. |
150 | * |
151 | * The rationale is that if the lock owner is running, it is likely to |
152 | * release the lock soon. |
153 | * |
154 | * Since this needs the lock owner, and this mutex implementation |
155 | * doesn't track the owner atomically in the lock field, we need to |
156 | * track it non-atomically. |
157 | * |
158 | * We can't do this for DEBUG_MUTEXES because that relies on wait_lock |
159 | * to serialize everything. |
160 | */ |
161 | |
162 | for (;;) { |
163 | struct task_struct *owner; |
164 | |
165 | /* |
166 | * If there's an owner, wait for it to either |
167 | * release the lock or go to sleep. |
168 | */ |
169 | owner = ACCESS_ONCE(lock->owner); |
170 | if (owner && !mutex_spin_on_owner(lock, owner)) |
171 | break; |
172 | |
173 | if (atomic_cmpxchg(&lock->count, 1, 0) == 1) { |
174 | lock_acquired(&lock->dep_map, ip); |
175 | mutex_set_owner(lock); |
176 | preempt_enable(); |
177 | return 0; |
178 | } |
179 | |
180 | /* |
181 | * When there's no owner, we might have preempted between the |
182 | * owner acquiring the lock and setting the owner field. If |
183 | * we're an RT task that will live-lock because we won't let |
184 | * the owner complete. |
185 | */ |
186 | if (!owner && (need_resched() || rt_task(task))) |
187 | break; |
188 | |
189 | /* |
190 | * The cpu_relax() call is a compiler barrier which forces |
191 | * everything in this loop to be re-loaded. We don't need |
192 | * memory barriers as we'll eventually observe the right |
193 | * values at the cost of a few extra spins. |
194 | */ |
195 | arch_mutex_cpu_relax(); |
196 | } |
197 | #endif |
198 | spin_lock_mutex(&lock->wait_lock, flags); |
199 | |
200 | debug_mutex_lock_common(lock, &waiter); |
201 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
202 | |
203 | /* add waiting tasks to the end of the waitqueue (FIFO): */ |
204 | list_add_tail(&waiter.list, &lock->wait_list); |
205 | waiter.task = task; |
206 | |
207 | if (atomic_xchg(&lock->count, -1) == 1) |
208 | goto done; |
209 | |
210 | lock_contended(&lock->dep_map, ip); |
211 | |
212 | for (;;) { |
213 | /* |
214 | * Lets try to take the lock again - this is needed even if |
215 | * we get here for the first time (shortly after failing to |
216 | * acquire the lock), to make sure that we get a wakeup once |
217 | * it's unlocked. Later on, if we sleep, this is the |
218 | * operation that gives us the lock. We xchg it to -1, so |
219 | * that when we release the lock, we properly wake up the |
220 | * other waiters: |
221 | */ |
222 | if (atomic_xchg(&lock->count, -1) == 1) |
223 | break; |
224 | |
225 | /* |
226 | * got a signal? (This code gets eliminated in the |
227 | * TASK_UNINTERRUPTIBLE case.) |
228 | */ |
229 | if (unlikely(signal_pending_state(state, task))) { |
230 | mutex_remove_waiter(lock, &waiter, |
231 | task_thread_info(task)); |
232 | mutex_release(&lock->dep_map, 1, ip); |
233 | spin_unlock_mutex(&lock->wait_lock, flags); |
234 | |
235 | debug_mutex_free_waiter(&waiter); |
236 | preempt_enable(); |
237 | return -EINTR; |
238 | } |
239 | __set_task_state(task, state); |
240 | |
241 | /* didn't get the lock, go to sleep: */ |
242 | spin_unlock_mutex(&lock->wait_lock, flags); |
243 | preempt_enable_no_resched(); |
244 | schedule(); |
245 | preempt_disable(); |
246 | spin_lock_mutex(&lock->wait_lock, flags); |
247 | } |
248 | |
249 | done: |
250 | lock_acquired(&lock->dep_map, ip); |
251 | /* got the lock - rejoice! */ |
252 | mutex_remove_waiter(lock, &waiter, current_thread_info()); |
253 | mutex_set_owner(lock); |
254 | |
255 | /* set it to 0 if there are no waiters left: */ |
256 | if (likely(list_empty(&lock->wait_list))) |
257 | atomic_set(&lock->count, 0); |
258 | |
259 | spin_unlock_mutex(&lock->wait_lock, flags); |
260 | |
261 | debug_mutex_free_waiter(&waiter); |
262 | preempt_enable(); |
263 | |
264 | return 0; |
265 | } |
266 | |
267 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
268 | void __sched |
269 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) |
270 | { |
271 | might_sleep(); |
272 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_); |
273 | } |
274 | |
275 | EXPORT_SYMBOL_GPL(mutex_lock_nested); |
276 | |
277 | void __sched |
278 | _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest) |
279 | { |
280 | might_sleep(); |
281 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_); |
282 | } |
283 | |
284 | EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); |
285 | |
286 | int __sched |
287 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) |
288 | { |
289 | might_sleep(); |
290 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_); |
291 | } |
292 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); |
293 | |
294 | int __sched |
295 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) |
296 | { |
297 | might_sleep(); |
298 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, |
299 | subclass, NULL, _RET_IP_); |
300 | } |
301 | |
302 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); |
303 | #endif |
304 | |
305 | /* |
306 | * Release the lock, slowpath: |
307 | */ |
308 | static inline void |
309 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) |
310 | { |
311 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
312 | unsigned long flags; |
313 | |
314 | spin_lock_mutex(&lock->wait_lock, flags); |
315 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
316 | debug_mutex_unlock(lock); |
317 | |
318 | /* |
319 | * some architectures leave the lock unlocked in the fastpath failure |
320 | * case, others need to leave it locked. In the later case we have to |
321 | * unlock it here |
322 | */ |
323 | if (__mutex_slowpath_needs_to_unlock()) |
324 | atomic_set(&lock->count, 1); |
325 | |
326 | if (!list_empty(&lock->wait_list)) { |
327 | /* get the first entry from the wait-list: */ |
328 | struct mutex_waiter *waiter = |
329 | list_entry(lock->wait_list.next, |
330 | struct mutex_waiter, list); |
331 | |
332 | debug_mutex_wake_waiter(lock, waiter); |
333 | |
334 | wake_up_process(waiter->task); |
335 | } |
336 | |
337 | spin_unlock_mutex(&lock->wait_lock, flags); |
338 | } |
339 | |
340 | /* |
341 | * Release the lock, slowpath: |
342 | */ |
343 | static __used noinline void |
344 | __mutex_unlock_slowpath(atomic_t *lock_count) |
345 | { |
346 | __mutex_unlock_common_slowpath(lock_count, 1); |
347 | } |
348 | |
349 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
350 | /* |
351 | * Here come the less common (and hence less performance-critical) APIs: |
352 | * mutex_lock_interruptible() and mutex_trylock(). |
353 | */ |
354 | static noinline int __sched |
355 | __mutex_lock_killable_slowpath(atomic_t *lock_count); |
356 | |
357 | static noinline int __sched |
358 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
359 | |
360 | /** |
361 | * mutex_lock_interruptible - acquire the mutex, interruptible |
362 | * @lock: the mutex to be acquired |
363 | * |
364 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has |
365 | * been acquired or sleep until the mutex becomes available. If a |
366 | * signal arrives while waiting for the lock then this function |
367 | * returns -EINTR. |
368 | * |
369 | * This function is similar to (but not equivalent to) down_interruptible(). |
370 | */ |
371 | int __sched mutex_lock_interruptible(struct mutex *lock) |
372 | { |
373 | int ret; |
374 | |
375 | might_sleep(); |
376 | ret = __mutex_fastpath_lock_retval |
377 | (&lock->count, __mutex_lock_interruptible_slowpath); |
378 | if (!ret) |
379 | mutex_set_owner(lock); |
380 | |
381 | return ret; |
382 | } |
383 | |
384 | EXPORT_SYMBOL(mutex_lock_interruptible); |
385 | |
386 | int __sched mutex_lock_killable(struct mutex *lock) |
387 | { |
388 | int ret; |
389 | |
390 | might_sleep(); |
391 | ret = __mutex_fastpath_lock_retval |
392 | (&lock->count, __mutex_lock_killable_slowpath); |
393 | if (!ret) |
394 | mutex_set_owner(lock); |
395 | |
396 | return ret; |
397 | } |
398 | EXPORT_SYMBOL(mutex_lock_killable); |
399 | |
400 | static __used noinline void __sched |
401 | __mutex_lock_slowpath(atomic_t *lock_count) |
402 | { |
403 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
404 | |
405 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_); |
406 | } |
407 | |
408 | static noinline int __sched |
409 | __mutex_lock_killable_slowpath(atomic_t *lock_count) |
410 | { |
411 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
412 | |
413 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, NULL, _RET_IP_); |
414 | } |
415 | |
416 | static noinline int __sched |
417 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
418 | { |
419 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
420 | |
421 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_); |
422 | } |
423 | #endif |
424 | |
425 | /* |
426 | * Spinlock based trylock, we take the spinlock and check whether we |
427 | * can get the lock: |
428 | */ |
429 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) |
430 | { |
431 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
432 | unsigned long flags; |
433 | int prev; |
434 | |
435 | spin_lock_mutex(&lock->wait_lock, flags); |
436 | |
437 | prev = atomic_xchg(&lock->count, -1); |
438 | if (likely(prev == 1)) { |
439 | mutex_set_owner(lock); |
440 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
441 | } |
442 | |
443 | /* Set it back to 0 if there are no waiters: */ |
444 | if (likely(list_empty(&lock->wait_list))) |
445 | atomic_set(&lock->count, 0); |
446 | |
447 | spin_unlock_mutex(&lock->wait_lock, flags); |
448 | |
449 | return prev == 1; |
450 | } |
451 | |
452 | /** |
453 | * mutex_trylock - try to acquire the mutex, without waiting |
454 | * @lock: the mutex to be acquired |
455 | * |
456 | * Try to acquire the mutex atomically. Returns 1 if the mutex |
457 | * has been acquired successfully, and 0 on contention. |
458 | * |
459 | * NOTE: this function follows the spin_trylock() convention, so |
460 | * it is negated from the down_trylock() return values! Be careful |
461 | * about this when converting semaphore users to mutexes. |
462 | * |
463 | * This function must not be used in interrupt context. The |
464 | * mutex must be released by the same task that acquired it. |
465 | */ |
466 | int __sched mutex_trylock(struct mutex *lock) |
467 | { |
468 | int ret; |
469 | |
470 | ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); |
471 | if (ret) |
472 | mutex_set_owner(lock); |
473 | |
474 | return ret; |
475 | } |
476 | EXPORT_SYMBOL(mutex_trylock); |
477 | |
478 | /** |
479 | * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 |
480 | * @cnt: the atomic which we are to dec |
481 | * @lock: the mutex to return holding if we dec to 0 |
482 | * |
483 | * return true and hold lock if we dec to 0, return false otherwise |
484 | */ |
485 | int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) |
486 | { |
487 | /* dec if we can't possibly hit 0 */ |
488 | if (atomic_add_unless(cnt, -1, 1)) |
489 | return 0; |
490 | /* we might hit 0, so take the lock */ |
491 | mutex_lock(lock); |
492 | if (!atomic_dec_and_test(cnt)) { |
493 | /* when we actually did the dec, we didn't hit 0 */ |
494 | mutex_unlock(lock); |
495 | return 0; |
496 | } |
497 | /* we hit 0, and we hold the lock */ |
498 | return 1; |
499 | } |
500 | EXPORT_SYMBOL(atomic_dec_and_mutex_lock); |
501 |
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