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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 | * | |
13 | * Also see Documentation/mutex-design.txt. | |
14 | */ | |
15 | #include <linux/mutex.h> | |
16 | #include <linux/sched.h> | |
17 | #include <linux/module.h> | |
18 | #include <linux/spinlock.h> | |
19 | #include <linux/interrupt.h> | |
9a11b49a | 20 | #include <linux/debug_locks.h> |
6053ee3b IM |
21 | |
22 | /* | |
23 | * In the DEBUG case we are using the "NULL fastpath" for mutexes, | |
24 | * which forces all calls into the slowpath: | |
25 | */ | |
26 | #ifdef CONFIG_DEBUG_MUTEXES | |
27 | # include "mutex-debug.h" | |
28 | # include <asm-generic/mutex-null.h> | |
29 | #else | |
30 | # include "mutex.h" | |
31 | # include <asm/mutex.h> | |
32 | #endif | |
33 | ||
34 | /*** | |
35 | * mutex_init - initialize the mutex | |
36 | * @lock: the mutex to be initialized | |
0e241ffd | 37 | * @key: the lock_class_key for the class; used by mutex lock debugging |
6053ee3b IM |
38 | * |
39 | * Initialize the mutex to unlocked state. | |
40 | * | |
41 | * It is not allowed to initialize an already locked mutex. | |
42 | */ | |
ef5d4707 IM |
43 | void |
44 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) | |
6053ee3b IM |
45 | { |
46 | atomic_set(&lock->count, 1); | |
47 | spin_lock_init(&lock->wait_lock); | |
48 | INIT_LIST_HEAD(&lock->wait_list); | |
49 | ||
ef5d4707 | 50 | debug_mutex_init(lock, name, key); |
6053ee3b IM |
51 | } |
52 | ||
53 | EXPORT_SYMBOL(__mutex_init); | |
54 | ||
e4564f79 | 55 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
56 | /* |
57 | * We split the mutex lock/unlock logic into separate fastpath and | |
58 | * slowpath functions, to reduce the register pressure on the fastpath. | |
59 | * We also put the fastpath first in the kernel image, to make sure the | |
60 | * branch is predicted by the CPU as default-untaken. | |
61 | */ | |
7918baa5 | 62 | static __used noinline void __sched |
9a11b49a | 63 | __mutex_lock_slowpath(atomic_t *lock_count); |
6053ee3b IM |
64 | |
65 | /*** | |
66 | * mutex_lock - acquire the mutex | |
67 | * @lock: the mutex to be acquired | |
68 | * | |
69 | * Lock the mutex exclusively for this task. If the mutex is not | |
70 | * available right now, it will sleep until it can get it. | |
71 | * | |
72 | * The mutex must later on be released by the same task that | |
73 | * acquired it. Recursive locking is not allowed. The task | |
74 | * may not exit without first unlocking the mutex. Also, kernel | |
75 | * memory where the mutex resides mutex must not be freed with | |
76 | * the mutex still locked. The mutex must first be initialized | |
77 | * (or statically defined) before it can be locked. memset()-ing | |
78 | * the mutex to 0 is not allowed. | |
79 | * | |
80 | * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging | |
81 | * checks that will enforce the restrictions and will also do | |
82 | * deadlock debugging. ) | |
83 | * | |
84 | * This function is similar to (but not equivalent to) down(). | |
85 | */ | |
7ad5b3a5 | 86 | void inline __sched mutex_lock(struct mutex *lock) |
6053ee3b | 87 | { |
c544bdb1 | 88 | might_sleep(); |
6053ee3b IM |
89 | /* |
90 | * The locking fastpath is the 1->0 transition from | |
91 | * 'unlocked' into 'locked' state. | |
6053ee3b IM |
92 | */ |
93 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); | |
94 | } | |
95 | ||
96 | EXPORT_SYMBOL(mutex_lock); | |
e4564f79 | 97 | #endif |
6053ee3b | 98 | |
7918baa5 | 99 | static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); |
6053ee3b IM |
100 | |
101 | /*** | |
102 | * mutex_unlock - release the mutex | |
103 | * @lock: the mutex to be released | |
104 | * | |
105 | * Unlock a mutex that has been locked by this task previously. | |
106 | * | |
107 | * This function must not be used in interrupt context. Unlocking | |
108 | * of a not locked mutex is not allowed. | |
109 | * | |
110 | * This function is similar to (but not equivalent to) up(). | |
111 | */ | |
7ad5b3a5 | 112 | void __sched mutex_unlock(struct mutex *lock) |
6053ee3b IM |
113 | { |
114 | /* | |
115 | * The unlocking fastpath is the 0->1 transition from 'locked' | |
116 | * into 'unlocked' state: | |
6053ee3b IM |
117 | */ |
118 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); | |
119 | } | |
120 | ||
121 | EXPORT_SYMBOL(mutex_unlock); | |
122 | ||
123 | /* | |
124 | * Lock a mutex (possibly interruptible), slowpath: | |
125 | */ | |
126 | static inline int __sched | |
e4564f79 PZ |
127 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
128 | unsigned long ip) | |
6053ee3b IM |
129 | { |
130 | struct task_struct *task = current; | |
131 | struct mutex_waiter waiter; | |
1fb00c6c | 132 | unsigned long flags; |
6053ee3b | 133 | |
41719b03 | 134 | preempt_disable(); |
1fb00c6c | 135 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b | 136 | |
9a11b49a | 137 | debug_mutex_lock_common(lock, &waiter); |
e4564f79 | 138 | mutex_acquire(&lock->dep_map, subclass, 0, ip); |
c9f4f06d | 139 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
6053ee3b IM |
140 | |
141 | /* add waiting tasks to the end of the waitqueue (FIFO): */ | |
142 | list_add_tail(&waiter.list, &lock->wait_list); | |
143 | waiter.task = task; | |
144 | ||
93d81d1a | 145 | if (atomic_xchg(&lock->count, -1) == 1) |
4fe87745 PZ |
146 | goto done; |
147 | ||
e4564f79 | 148 | lock_contended(&lock->dep_map, ip); |
4fe87745 | 149 | |
6053ee3b IM |
150 | for (;;) { |
151 | /* | |
152 | * Lets try to take the lock again - this is needed even if | |
153 | * we get here for the first time (shortly after failing to | |
154 | * acquire the lock), to make sure that we get a wakeup once | |
155 | * it's unlocked. Later on, if we sleep, this is the | |
156 | * operation that gives us the lock. We xchg it to -1, so | |
157 | * that when we release the lock, we properly wake up the | |
158 | * other waiters: | |
159 | */ | |
93d81d1a | 160 | if (atomic_xchg(&lock->count, -1) == 1) |
6053ee3b IM |
161 | break; |
162 | ||
163 | /* | |
164 | * got a signal? (This code gets eliminated in the | |
165 | * TASK_UNINTERRUPTIBLE case.) | |
166 | */ | |
6ad36762 | 167 | if (unlikely(signal_pending_state(state, task))) { |
ad776537 LH |
168 | mutex_remove_waiter(lock, &waiter, |
169 | task_thread_info(task)); | |
e4564f79 | 170 | mutex_release(&lock->dep_map, 1, ip); |
1fb00c6c | 171 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
172 | |
173 | debug_mutex_free_waiter(&waiter); | |
41719b03 | 174 | preempt_enable(); |
6053ee3b IM |
175 | return -EINTR; |
176 | } | |
177 | __set_task_state(task, state); | |
178 | ||
179 | /* didnt get the lock, go to sleep: */ | |
1fb00c6c | 180 | spin_unlock_mutex(&lock->wait_lock, flags); |
41719b03 | 181 | __schedule(); |
1fb00c6c | 182 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
183 | } |
184 | ||
4fe87745 | 185 | done: |
c7e78cff | 186 | lock_acquired(&lock->dep_map, ip); |
6053ee3b | 187 | /* got the lock - rejoice! */ |
c9f4f06d RZ |
188 | mutex_remove_waiter(lock, &waiter, task_thread_info(task)); |
189 | debug_mutex_set_owner(lock, task_thread_info(task)); | |
6053ee3b IM |
190 | |
191 | /* set it to 0 if there are no waiters left: */ | |
192 | if (likely(list_empty(&lock->wait_list))) | |
193 | atomic_set(&lock->count, 0); | |
194 | ||
1fb00c6c | 195 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
196 | |
197 | debug_mutex_free_waiter(&waiter); | |
41719b03 | 198 | preempt_enable(); |
6053ee3b | 199 | |
6053ee3b IM |
200 | return 0; |
201 | } | |
202 | ||
ef5d4707 IM |
203 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
204 | void __sched | |
205 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) | |
206 | { | |
207 | might_sleep(); | |
e4564f79 | 208 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_); |
ef5d4707 IM |
209 | } |
210 | ||
211 | EXPORT_SYMBOL_GPL(mutex_lock_nested); | |
d63a5a74 | 212 | |
ad776537 LH |
213 | int __sched |
214 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) | |
215 | { | |
216 | might_sleep(); | |
217 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_); | |
218 | } | |
219 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); | |
220 | ||
d63a5a74 N |
221 | int __sched |
222 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) | |
223 | { | |
224 | might_sleep(); | |
e4564f79 | 225 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_); |
d63a5a74 N |
226 | } |
227 | ||
228 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); | |
ef5d4707 IM |
229 | #endif |
230 | ||
6053ee3b IM |
231 | /* |
232 | * Release the lock, slowpath: | |
233 | */ | |
7ad5b3a5 | 234 | static inline void |
ef5d4707 | 235 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) |
6053ee3b | 236 | { |
02706647 | 237 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
1fb00c6c | 238 | unsigned long flags; |
6053ee3b | 239 | |
1fb00c6c | 240 | spin_lock_mutex(&lock->wait_lock, flags); |
ef5d4707 | 241 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
9a11b49a | 242 | debug_mutex_unlock(lock); |
6053ee3b IM |
243 | |
244 | /* | |
245 | * some architectures leave the lock unlocked in the fastpath failure | |
246 | * case, others need to leave it locked. In the later case we have to | |
247 | * unlock it here | |
248 | */ | |
249 | if (__mutex_slowpath_needs_to_unlock()) | |
250 | atomic_set(&lock->count, 1); | |
251 | ||
6053ee3b IM |
252 | if (!list_empty(&lock->wait_list)) { |
253 | /* get the first entry from the wait-list: */ | |
254 | struct mutex_waiter *waiter = | |
255 | list_entry(lock->wait_list.next, | |
256 | struct mutex_waiter, list); | |
257 | ||
258 | debug_mutex_wake_waiter(lock, waiter); | |
259 | ||
260 | wake_up_process(waiter->task); | |
261 | } | |
262 | ||
263 | debug_mutex_clear_owner(lock); | |
264 | ||
1fb00c6c | 265 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
266 | } |
267 | ||
9a11b49a IM |
268 | /* |
269 | * Release the lock, slowpath: | |
270 | */ | |
7918baa5 | 271 | static __used noinline void |
9a11b49a IM |
272 | __mutex_unlock_slowpath(atomic_t *lock_count) |
273 | { | |
ef5d4707 | 274 | __mutex_unlock_common_slowpath(lock_count, 1); |
9a11b49a IM |
275 | } |
276 | ||
e4564f79 | 277 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
278 | /* |
279 | * Here come the less common (and hence less performance-critical) APIs: | |
280 | * mutex_lock_interruptible() and mutex_trylock(). | |
281 | */ | |
7ad5b3a5 | 282 | static noinline int __sched |
ad776537 LH |
283 | __mutex_lock_killable_slowpath(atomic_t *lock_count); |
284 | ||
7ad5b3a5 | 285 | static noinline int __sched |
9a11b49a | 286 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
6053ee3b IM |
287 | |
288 | /*** | |
289 | * mutex_lock_interruptible - acquire the mutex, interruptable | |
290 | * @lock: the mutex to be acquired | |
291 | * | |
292 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has | |
293 | * been acquired or sleep until the mutex becomes available. If a | |
294 | * signal arrives while waiting for the lock then this function | |
295 | * returns -EINTR. | |
296 | * | |
297 | * This function is similar to (but not equivalent to) down_interruptible(). | |
298 | */ | |
7ad5b3a5 | 299 | int __sched mutex_lock_interruptible(struct mutex *lock) |
6053ee3b | 300 | { |
c544bdb1 | 301 | might_sleep(); |
6053ee3b IM |
302 | return __mutex_fastpath_lock_retval |
303 | (&lock->count, __mutex_lock_interruptible_slowpath); | |
304 | } | |
305 | ||
306 | EXPORT_SYMBOL(mutex_lock_interruptible); | |
307 | ||
7ad5b3a5 | 308 | int __sched mutex_lock_killable(struct mutex *lock) |
ad776537 LH |
309 | { |
310 | might_sleep(); | |
311 | return __mutex_fastpath_lock_retval | |
312 | (&lock->count, __mutex_lock_killable_slowpath); | |
313 | } | |
314 | EXPORT_SYMBOL(mutex_lock_killable); | |
315 | ||
7918baa5 | 316 | static __used noinline void __sched |
e4564f79 PZ |
317 | __mutex_lock_slowpath(atomic_t *lock_count) |
318 | { | |
319 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
320 | ||
321 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_); | |
322 | } | |
323 | ||
7ad5b3a5 | 324 | static noinline int __sched |
ad776537 LH |
325 | __mutex_lock_killable_slowpath(atomic_t *lock_count) |
326 | { | |
327 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
328 | ||
329 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_); | |
330 | } | |
331 | ||
7ad5b3a5 | 332 | static noinline int __sched |
9a11b49a | 333 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
6053ee3b IM |
334 | { |
335 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
336 | ||
e4564f79 | 337 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_); |
6053ee3b | 338 | } |
e4564f79 | 339 | #endif |
6053ee3b IM |
340 | |
341 | /* | |
342 | * Spinlock based trylock, we take the spinlock and check whether we | |
343 | * can get the lock: | |
344 | */ | |
345 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) | |
346 | { | |
347 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
1fb00c6c | 348 | unsigned long flags; |
6053ee3b IM |
349 | int prev; |
350 | ||
1fb00c6c | 351 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
352 | |
353 | prev = atomic_xchg(&lock->count, -1); | |
ef5d4707 | 354 | if (likely(prev == 1)) { |
9a11b49a | 355 | debug_mutex_set_owner(lock, current_thread_info()); |
ef5d4707 IM |
356 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
357 | } | |
6053ee3b IM |
358 | /* Set it back to 0 if there are no waiters: */ |
359 | if (likely(list_empty(&lock->wait_list))) | |
360 | atomic_set(&lock->count, 0); | |
361 | ||
1fb00c6c | 362 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
363 | |
364 | return prev == 1; | |
365 | } | |
366 | ||
367 | /*** | |
368 | * mutex_trylock - try acquire the mutex, without waiting | |
369 | * @lock: the mutex to be acquired | |
370 | * | |
371 | * Try to acquire the mutex atomically. Returns 1 if the mutex | |
372 | * has been acquired successfully, and 0 on contention. | |
373 | * | |
374 | * NOTE: this function follows the spin_trylock() convention, so | |
375 | * it is negated to the down_trylock() return values! Be careful | |
376 | * about this when converting semaphore users to mutexes. | |
377 | * | |
378 | * This function must not be used in interrupt context. The | |
379 | * mutex must be released by the same task that acquired it. | |
380 | */ | |
7ad5b3a5 | 381 | int __sched mutex_trylock(struct mutex *lock) |
6053ee3b IM |
382 | { |
383 | return __mutex_fastpath_trylock(&lock->count, | |
384 | __mutex_trylock_slowpath); | |
385 | } | |
386 | ||
387 | EXPORT_SYMBOL(mutex_trylock); |