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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 | |
1fb00c6c | 134 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b | 135 | |
9a11b49a | 136 | debug_mutex_lock_common(lock, &waiter); |
e4564f79 | 137 | mutex_acquire(&lock->dep_map, subclass, 0, ip); |
c9f4f06d | 138 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
6053ee3b IM |
139 | |
140 | /* add waiting tasks to the end of the waitqueue (FIFO): */ | |
141 | list_add_tail(&waiter.list, &lock->wait_list); | |
142 | waiter.task = task; | |
143 | ||
93d81d1a | 144 | if (atomic_xchg(&lock->count, -1) == 1) |
4fe87745 PZ |
145 | goto done; |
146 | ||
e4564f79 | 147 | lock_contended(&lock->dep_map, ip); |
4fe87745 | 148 | |
6053ee3b IM |
149 | for (;;) { |
150 | /* | |
151 | * Lets try to take the lock again - this is needed even if | |
152 | * we get here for the first time (shortly after failing to | |
153 | * acquire the lock), to make sure that we get a wakeup once | |
154 | * it's unlocked. Later on, if we sleep, this is the | |
155 | * operation that gives us the lock. We xchg it to -1, so | |
156 | * that when we release the lock, we properly wake up the | |
157 | * other waiters: | |
158 | */ | |
93d81d1a | 159 | if (atomic_xchg(&lock->count, -1) == 1) |
6053ee3b IM |
160 | break; |
161 | ||
162 | /* | |
163 | * got a signal? (This code gets eliminated in the | |
164 | * TASK_UNINTERRUPTIBLE case.) | |
165 | */ | |
6ad36762 | 166 | if (unlikely(signal_pending_state(state, task))) { |
ad776537 LH |
167 | mutex_remove_waiter(lock, &waiter, |
168 | task_thread_info(task)); | |
e4564f79 | 169 | mutex_release(&lock->dep_map, 1, ip); |
1fb00c6c | 170 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
171 | |
172 | debug_mutex_free_waiter(&waiter); | |
173 | return -EINTR; | |
174 | } | |
175 | __set_task_state(task, state); | |
176 | ||
177 | /* didnt get the lock, go to sleep: */ | |
1fb00c6c | 178 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b | 179 | schedule(); |
1fb00c6c | 180 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
181 | } |
182 | ||
4fe87745 | 183 | done: |
c7e78cff | 184 | lock_acquired(&lock->dep_map, ip); |
6053ee3b | 185 | /* got the lock - rejoice! */ |
c9f4f06d RZ |
186 | mutex_remove_waiter(lock, &waiter, task_thread_info(task)); |
187 | debug_mutex_set_owner(lock, task_thread_info(task)); | |
6053ee3b IM |
188 | |
189 | /* set it to 0 if there are no waiters left: */ | |
190 | if (likely(list_empty(&lock->wait_list))) | |
191 | atomic_set(&lock->count, 0); | |
192 | ||
1fb00c6c | 193 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
194 | |
195 | debug_mutex_free_waiter(&waiter); | |
196 | ||
6053ee3b IM |
197 | return 0; |
198 | } | |
199 | ||
ef5d4707 IM |
200 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
201 | void __sched | |
202 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) | |
203 | { | |
204 | might_sleep(); | |
e4564f79 | 205 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_); |
ef5d4707 IM |
206 | } |
207 | ||
208 | EXPORT_SYMBOL_GPL(mutex_lock_nested); | |
d63a5a74 | 209 | |
ad776537 LH |
210 | int __sched |
211 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) | |
212 | { | |
213 | might_sleep(); | |
214 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_); | |
215 | } | |
216 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); | |
217 | ||
d63a5a74 N |
218 | int __sched |
219 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) | |
220 | { | |
221 | might_sleep(); | |
e4564f79 | 222 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_); |
d63a5a74 N |
223 | } |
224 | ||
225 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); | |
ef5d4707 IM |
226 | #endif |
227 | ||
6053ee3b IM |
228 | /* |
229 | * Release the lock, slowpath: | |
230 | */ | |
7ad5b3a5 | 231 | static inline void |
ef5d4707 | 232 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) |
6053ee3b | 233 | { |
02706647 | 234 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
1fb00c6c | 235 | unsigned long flags; |
6053ee3b | 236 | |
1fb00c6c | 237 | spin_lock_mutex(&lock->wait_lock, flags); |
ef5d4707 | 238 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
9a11b49a | 239 | debug_mutex_unlock(lock); |
6053ee3b IM |
240 | |
241 | /* | |
242 | * some architectures leave the lock unlocked in the fastpath failure | |
243 | * case, others need to leave it locked. In the later case we have to | |
244 | * unlock it here | |
245 | */ | |
246 | if (__mutex_slowpath_needs_to_unlock()) | |
247 | atomic_set(&lock->count, 1); | |
248 | ||
6053ee3b IM |
249 | if (!list_empty(&lock->wait_list)) { |
250 | /* get the first entry from the wait-list: */ | |
251 | struct mutex_waiter *waiter = | |
252 | list_entry(lock->wait_list.next, | |
253 | struct mutex_waiter, list); | |
254 | ||
255 | debug_mutex_wake_waiter(lock, waiter); | |
256 | ||
257 | wake_up_process(waiter->task); | |
258 | } | |
259 | ||
260 | debug_mutex_clear_owner(lock); | |
261 | ||
1fb00c6c | 262 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
263 | } |
264 | ||
9a11b49a IM |
265 | /* |
266 | * Release the lock, slowpath: | |
267 | */ | |
7918baa5 | 268 | static __used noinline void |
9a11b49a IM |
269 | __mutex_unlock_slowpath(atomic_t *lock_count) |
270 | { | |
ef5d4707 | 271 | __mutex_unlock_common_slowpath(lock_count, 1); |
9a11b49a IM |
272 | } |
273 | ||
e4564f79 | 274 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
275 | /* |
276 | * Here come the less common (and hence less performance-critical) APIs: | |
277 | * mutex_lock_interruptible() and mutex_trylock(). | |
278 | */ | |
7ad5b3a5 | 279 | static noinline int __sched |
ad776537 LH |
280 | __mutex_lock_killable_slowpath(atomic_t *lock_count); |
281 | ||
7ad5b3a5 | 282 | static noinline int __sched |
9a11b49a | 283 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
6053ee3b IM |
284 | |
285 | /*** | |
286 | * mutex_lock_interruptible - acquire the mutex, interruptable | |
287 | * @lock: the mutex to be acquired | |
288 | * | |
289 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has | |
290 | * been acquired or sleep until the mutex becomes available. If a | |
291 | * signal arrives while waiting for the lock then this function | |
292 | * returns -EINTR. | |
293 | * | |
294 | * This function is similar to (but not equivalent to) down_interruptible(). | |
295 | */ | |
7ad5b3a5 | 296 | int __sched mutex_lock_interruptible(struct mutex *lock) |
6053ee3b | 297 | { |
c544bdb1 | 298 | might_sleep(); |
6053ee3b IM |
299 | return __mutex_fastpath_lock_retval |
300 | (&lock->count, __mutex_lock_interruptible_slowpath); | |
301 | } | |
302 | ||
303 | EXPORT_SYMBOL(mutex_lock_interruptible); | |
304 | ||
7ad5b3a5 | 305 | int __sched mutex_lock_killable(struct mutex *lock) |
ad776537 LH |
306 | { |
307 | might_sleep(); | |
308 | return __mutex_fastpath_lock_retval | |
309 | (&lock->count, __mutex_lock_killable_slowpath); | |
310 | } | |
311 | EXPORT_SYMBOL(mutex_lock_killable); | |
312 | ||
7918baa5 | 313 | static __used noinline void __sched |
e4564f79 PZ |
314 | __mutex_lock_slowpath(atomic_t *lock_count) |
315 | { | |
316 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
317 | ||
318 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_); | |
319 | } | |
320 | ||
7ad5b3a5 | 321 | static noinline int __sched |
ad776537 LH |
322 | __mutex_lock_killable_slowpath(atomic_t *lock_count) |
323 | { | |
324 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
325 | ||
326 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_); | |
327 | } | |
328 | ||
7ad5b3a5 | 329 | static noinline int __sched |
9a11b49a | 330 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
6053ee3b IM |
331 | { |
332 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
333 | ||
e4564f79 | 334 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_); |
6053ee3b | 335 | } |
e4564f79 | 336 | #endif |
6053ee3b IM |
337 | |
338 | /* | |
339 | * Spinlock based trylock, we take the spinlock and check whether we | |
340 | * can get the lock: | |
341 | */ | |
342 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) | |
343 | { | |
344 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
1fb00c6c | 345 | unsigned long flags; |
6053ee3b IM |
346 | int prev; |
347 | ||
1fb00c6c | 348 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
349 | |
350 | prev = atomic_xchg(&lock->count, -1); | |
ef5d4707 | 351 | if (likely(prev == 1)) { |
9a11b49a | 352 | debug_mutex_set_owner(lock, current_thread_info()); |
ef5d4707 IM |
353 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
354 | } | |
6053ee3b IM |
355 | /* Set it back to 0 if there are no waiters: */ |
356 | if (likely(list_empty(&lock->wait_list))) | |
357 | atomic_set(&lock->count, 0); | |
358 | ||
1fb00c6c | 359 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
360 | |
361 | return prev == 1; | |
362 | } | |
363 | ||
364 | /*** | |
365 | * mutex_trylock - try acquire the mutex, without waiting | |
366 | * @lock: the mutex to be acquired | |
367 | * | |
368 | * Try to acquire the mutex atomically. Returns 1 if the mutex | |
369 | * has been acquired successfully, and 0 on contention. | |
370 | * | |
371 | * NOTE: this function follows the spin_trylock() convention, so | |
372 | * it is negated to the down_trylock() return values! Be careful | |
373 | * about this when converting semaphore users to mutexes. | |
374 | * | |
375 | * This function must not be used in interrupt context. The | |
376 | * mutex must be released by the same task that acquired it. | |
377 | */ | |
7ad5b3a5 | 378 | int __sched mutex_trylock(struct mutex *lock) |
6053ee3b IM |
379 | { |
380 | return __mutex_fastpath_trylock(&lock->count, | |
381 | __mutex_trylock_slowpath); | |
382 | } | |
383 | ||
384 | EXPORT_SYMBOL(mutex_trylock); |