]>
Commit | Line | Data |
---|---|---|
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 | |
37 | * | |
38 | * Initialize the mutex to unlocked state. | |
39 | * | |
40 | * It is not allowed to initialize an already locked mutex. | |
41 | */ | |
9a11b49a | 42 | __always_inline void fastcall __mutex_init(struct mutex *lock, const char *name) |
6053ee3b IM |
43 | { |
44 | atomic_set(&lock->count, 1); | |
45 | spin_lock_init(&lock->wait_lock); | |
46 | INIT_LIST_HEAD(&lock->wait_list); | |
47 | ||
48 | debug_mutex_init(lock, name); | |
49 | } | |
50 | ||
51 | EXPORT_SYMBOL(__mutex_init); | |
52 | ||
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 void fastcall noinline __sched | |
9a11b49a | 60 | __mutex_lock_slowpath(atomic_t *lock_count); |
6053ee3b IM |
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 | */ | |
9a11b49a | 83 | void inline fastcall __sched mutex_lock(struct mutex *lock) |
6053ee3b | 84 | { |
c544bdb1 | 85 | might_sleep(); |
6053ee3b IM |
86 | /* |
87 | * The locking fastpath is the 1->0 transition from | |
88 | * 'unlocked' into 'locked' state. | |
6053ee3b IM |
89 | */ |
90 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); | |
91 | } | |
92 | ||
93 | EXPORT_SYMBOL(mutex_lock); | |
94 | ||
95 | static void fastcall noinline __sched | |
9a11b49a | 96 | __mutex_unlock_slowpath(atomic_t *lock_count); |
6053ee3b IM |
97 | |
98 | /*** | |
99 | * mutex_unlock - release the mutex | |
100 | * @lock: the mutex to be released | |
101 | * | |
102 | * Unlock a mutex that has been locked by this task previously. | |
103 | * | |
104 | * This function must not be used in interrupt context. Unlocking | |
105 | * of a not locked mutex is not allowed. | |
106 | * | |
107 | * This function is similar to (but not equivalent to) up(). | |
108 | */ | |
109 | void fastcall __sched mutex_unlock(struct mutex *lock) | |
110 | { | |
111 | /* | |
112 | * The unlocking fastpath is the 0->1 transition from 'locked' | |
113 | * into 'unlocked' state: | |
6053ee3b IM |
114 | */ |
115 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); | |
116 | } | |
117 | ||
118 | EXPORT_SYMBOL(mutex_unlock); | |
119 | ||
120 | /* | |
121 | * Lock a mutex (possibly interruptible), slowpath: | |
122 | */ | |
123 | static inline int __sched | |
9a11b49a | 124 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass) |
6053ee3b IM |
125 | { |
126 | struct task_struct *task = current; | |
127 | struct mutex_waiter waiter; | |
128 | unsigned int old_val; | |
1fb00c6c | 129 | unsigned long flags; |
6053ee3b | 130 | |
1fb00c6c | 131 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b | 132 | |
9a11b49a IM |
133 | debug_mutex_lock_common(lock, &waiter); |
134 | debug_mutex_add_waiter(lock, &waiter, task->thread_info); | |
6053ee3b IM |
135 | |
136 | /* add waiting tasks to the end of the waitqueue (FIFO): */ | |
137 | list_add_tail(&waiter.list, &lock->wait_list); | |
138 | waiter.task = task; | |
139 | ||
140 | for (;;) { | |
141 | /* | |
142 | * Lets try to take the lock again - this is needed even if | |
143 | * we get here for the first time (shortly after failing to | |
144 | * acquire the lock), to make sure that we get a wakeup once | |
145 | * it's unlocked. Later on, if we sleep, this is the | |
146 | * operation that gives us the lock. We xchg it to -1, so | |
147 | * that when we release the lock, we properly wake up the | |
148 | * other waiters: | |
149 | */ | |
150 | old_val = atomic_xchg(&lock->count, -1); | |
151 | if (old_val == 1) | |
152 | break; | |
153 | ||
154 | /* | |
155 | * got a signal? (This code gets eliminated in the | |
156 | * TASK_UNINTERRUPTIBLE case.) | |
157 | */ | |
158 | if (unlikely(state == TASK_INTERRUPTIBLE && | |
159 | signal_pending(task))) { | |
160 | mutex_remove_waiter(lock, &waiter, task->thread_info); | |
1fb00c6c | 161 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
162 | |
163 | debug_mutex_free_waiter(&waiter); | |
164 | return -EINTR; | |
165 | } | |
166 | __set_task_state(task, state); | |
167 | ||
168 | /* didnt get the lock, go to sleep: */ | |
1fb00c6c | 169 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b | 170 | schedule(); |
1fb00c6c | 171 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
172 | } |
173 | ||
174 | /* got the lock - rejoice! */ | |
175 | mutex_remove_waiter(lock, &waiter, task->thread_info); | |
9a11b49a | 176 | debug_mutex_set_owner(lock, task->thread_info); |
6053ee3b IM |
177 | |
178 | /* set it to 0 if there are no waiters left: */ | |
179 | if (likely(list_empty(&lock->wait_list))) | |
180 | atomic_set(&lock->count, 0); | |
181 | ||
1fb00c6c | 182 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
183 | |
184 | debug_mutex_free_waiter(&waiter); | |
185 | ||
6053ee3b IM |
186 | return 0; |
187 | } | |
188 | ||
189 | static void fastcall noinline __sched | |
9a11b49a | 190 | __mutex_lock_slowpath(atomic_t *lock_count) |
6053ee3b IM |
191 | { |
192 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
193 | ||
9a11b49a | 194 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0); |
6053ee3b IM |
195 | } |
196 | ||
197 | /* | |
198 | * Release the lock, slowpath: | |
199 | */ | |
9a11b49a IM |
200 | static fastcall inline void |
201 | __mutex_unlock_common_slowpath(atomic_t *lock_count) | |
6053ee3b | 202 | { |
02706647 | 203 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
1fb00c6c | 204 | unsigned long flags; |
6053ee3b | 205 | |
1fb00c6c | 206 | spin_lock_mutex(&lock->wait_lock, flags); |
9a11b49a | 207 | debug_mutex_unlock(lock); |
6053ee3b IM |
208 | |
209 | /* | |
210 | * some architectures leave the lock unlocked in the fastpath failure | |
211 | * case, others need to leave it locked. In the later case we have to | |
212 | * unlock it here | |
213 | */ | |
214 | if (__mutex_slowpath_needs_to_unlock()) | |
215 | atomic_set(&lock->count, 1); | |
216 | ||
6053ee3b IM |
217 | if (!list_empty(&lock->wait_list)) { |
218 | /* get the first entry from the wait-list: */ | |
219 | struct mutex_waiter *waiter = | |
220 | list_entry(lock->wait_list.next, | |
221 | struct mutex_waiter, list); | |
222 | ||
223 | debug_mutex_wake_waiter(lock, waiter); | |
224 | ||
225 | wake_up_process(waiter->task); | |
226 | } | |
227 | ||
228 | debug_mutex_clear_owner(lock); | |
229 | ||
1fb00c6c | 230 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
231 | } |
232 | ||
9a11b49a IM |
233 | /* |
234 | * Release the lock, slowpath: | |
235 | */ | |
236 | static fastcall noinline void | |
237 | __mutex_unlock_slowpath(atomic_t *lock_count) | |
238 | { | |
239 | __mutex_unlock_common_slowpath(lock_count); | |
240 | } | |
241 | ||
6053ee3b IM |
242 | /* |
243 | * Here come the less common (and hence less performance-critical) APIs: | |
244 | * mutex_lock_interruptible() and mutex_trylock(). | |
245 | */ | |
246 | static int fastcall noinline __sched | |
9a11b49a | 247 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
6053ee3b IM |
248 | |
249 | /*** | |
250 | * mutex_lock_interruptible - acquire the mutex, interruptable | |
251 | * @lock: the mutex to be acquired | |
252 | * | |
253 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has | |
254 | * been acquired or sleep until the mutex becomes available. If a | |
255 | * signal arrives while waiting for the lock then this function | |
256 | * returns -EINTR. | |
257 | * | |
258 | * This function is similar to (but not equivalent to) down_interruptible(). | |
259 | */ | |
260 | int fastcall __sched mutex_lock_interruptible(struct mutex *lock) | |
261 | { | |
c544bdb1 | 262 | might_sleep(); |
6053ee3b IM |
263 | return __mutex_fastpath_lock_retval |
264 | (&lock->count, __mutex_lock_interruptible_slowpath); | |
265 | } | |
266 | ||
267 | EXPORT_SYMBOL(mutex_lock_interruptible); | |
268 | ||
269 | static int fastcall noinline __sched | |
9a11b49a | 270 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
6053ee3b IM |
271 | { |
272 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
273 | ||
9a11b49a | 274 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0); |
6053ee3b IM |
275 | } |
276 | ||
277 | /* | |
278 | * Spinlock based trylock, we take the spinlock and check whether we | |
279 | * can get the lock: | |
280 | */ | |
281 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) | |
282 | { | |
283 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
1fb00c6c | 284 | unsigned long flags; |
6053ee3b IM |
285 | int prev; |
286 | ||
1fb00c6c | 287 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
288 | |
289 | prev = atomic_xchg(&lock->count, -1); | |
290 | if (likely(prev == 1)) | |
9a11b49a IM |
291 | debug_mutex_set_owner(lock, current_thread_info()); |
292 | ||
6053ee3b IM |
293 | /* Set it back to 0 if there are no waiters: */ |
294 | if (likely(list_empty(&lock->wait_list))) | |
295 | atomic_set(&lock->count, 0); | |
296 | ||
1fb00c6c | 297 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
298 | |
299 | return prev == 1; | |
300 | } | |
301 | ||
302 | /*** | |
303 | * mutex_trylock - try acquire the mutex, without waiting | |
304 | * @lock: the mutex to be acquired | |
305 | * | |
306 | * Try to acquire the mutex atomically. Returns 1 if the mutex | |
307 | * has been acquired successfully, and 0 on contention. | |
308 | * | |
309 | * NOTE: this function follows the spin_trylock() convention, so | |
310 | * it is negated to the down_trylock() return values! Be careful | |
311 | * about this when converting semaphore users to mutexes. | |
312 | * | |
313 | * This function must not be used in interrupt context. The | |
314 | * mutex must be released by the same task that acquired it. | |
315 | */ | |
9cebb552 | 316 | int fastcall __sched mutex_trylock(struct mutex *lock) |
6053ee3b IM |
317 | { |
318 | return __mutex_fastpath_trylock(&lock->count, | |
319 | __mutex_trylock_slowpath); | |
320 | } | |
321 | ||
322 | EXPORT_SYMBOL(mutex_trylock); |