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>
20
21 /*
22 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
23 * which forces all calls into the slowpath:
24 */
25 #ifdef CONFIG_DEBUG_MUTEXES
26 # include "mutex-debug.h"
27 # include <asm-generic/mutex-null.h>
28 #else
29 # include "mutex.h"
30 # include <asm/mutex.h>
31 #endif
32
33 /***
34 * mutex_init - initialize the mutex
35 * @lock: the mutex to be initialized
36 *
37 * Initialize the mutex to unlocked state.
38 *
39 * It is not allowed to initialize an already locked mutex.
40 */
41 void fastcall __mutex_init(struct mutex *lock, const char *name)
42 {
43 atomic_set(&lock->count, 1);
44 spin_lock_init(&lock->wait_lock);
45 INIT_LIST_HEAD(&lock->wait_list);
46
47 debug_mutex_init(lock, name);
48 }
49
50 EXPORT_SYMBOL(__mutex_init);
51
52 /*
53 * We split the mutex lock/unlock logic into separate fastpath and
54 * slowpath functions, to reduce the register pressure on the fastpath.
55 * We also put the fastpath first in the kernel image, to make sure the
56 * branch is predicted by the CPU as default-untaken.
57 */
58 static void fastcall noinline __sched
59 __mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__);
60
61 /***
62 * mutex_lock - acquire the mutex
63 * @lock: the mutex to be acquired
64 *
65 * Lock the mutex exclusively for this task. If the mutex is not
66 * available right now, it will sleep until it can get it.
67 *
68 * The mutex must later on be released by the same task that
69 * acquired it. Recursive locking is not allowed. The task
70 * may not exit without first unlocking the mutex. Also, kernel
71 * memory where the mutex resides mutex must not be freed with
72 * the mutex still locked. The mutex must first be initialized
73 * (or statically defined) before it can be locked. memset()-ing
74 * the mutex to 0 is not allowed.
75 *
76 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
77 * checks that will enforce the restrictions and will also do
78 * deadlock debugging. )
79 *
80 * This function is similar to (but not equivalent to) down().
81 */
82 void fastcall __sched mutex_lock(struct mutex *lock)
83 {
84 might_sleep();
85 /*
86 * The locking fastpath is the 1->0 transition from
87 * 'unlocked' into 'locked' state.
88 */
89 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
90 }
91
92 EXPORT_SYMBOL(mutex_lock);
93
94 static void fastcall noinline __sched
95 __mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__);
96
97 /***
98 * mutex_unlock - release the mutex
99 * @lock: the mutex to be released
100 *
101 * Unlock a mutex that has been locked by this task previously.
102 *
103 * This function must not be used in interrupt context. Unlocking
104 * of a not locked mutex is not allowed.
105 *
106 * This function is similar to (but not equivalent to) up().
107 */
108 void fastcall __sched mutex_unlock(struct mutex *lock)
109 {
110 /*
111 * The unlocking fastpath is the 0->1 transition from 'locked'
112 * into 'unlocked' state:
113 */
114 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
115 }
116
117 EXPORT_SYMBOL(mutex_unlock);
118
119 /*
120 * Lock a mutex (possibly interruptible), slowpath:
121 */
122 static inline int __sched
123 __mutex_lock_common(struct mutex *lock, long state __IP_DECL__)
124 {
125 struct task_struct *task = current;
126 struct mutex_waiter waiter;
127 unsigned int old_val;
128
129 debug_mutex_init_waiter(&waiter);
130
131 spin_lock_mutex(&lock->wait_lock);
132
133 debug_mutex_add_waiter(lock, &waiter, task->thread_info, ip);
134
135 /* add waiting tasks to the end of the waitqueue (FIFO): */
136 list_add_tail(&waiter.list, &lock->wait_list);
137 waiter.task = task;
138
139 for (;;) {
140 /*
141 * Lets try to take the lock again - this is needed even if
142 * we get here for the first time (shortly after failing to
143 * acquire the lock), to make sure that we get a wakeup once
144 * it's unlocked. Later on, if we sleep, this is the
145 * operation that gives us the lock. We xchg it to -1, so
146 * that when we release the lock, we properly wake up the
147 * other waiters:
148 */
149 old_val = atomic_xchg(&lock->count, -1);
150 if (old_val == 1)
151 break;
152
153 /*
154 * got a signal? (This code gets eliminated in the
155 * TASK_UNINTERRUPTIBLE case.)
156 */
157 if (unlikely(state == TASK_INTERRUPTIBLE &&
158 signal_pending(task))) {
159 mutex_remove_waiter(lock, &waiter, task->thread_info);
160 spin_unlock_mutex(&lock->wait_lock);
161
162 debug_mutex_free_waiter(&waiter);
163 return -EINTR;
164 }
165 __set_task_state(task, state);
166
167 /* didnt get the lock, go to sleep: */
168 spin_unlock_mutex(&lock->wait_lock);
169 schedule();
170 spin_lock_mutex(&lock->wait_lock);
171 }
172
173 /* got the lock - rejoice! */
174 mutex_remove_waiter(lock, &waiter, task->thread_info);
175 debug_mutex_set_owner(lock, task->thread_info __IP__);
176
177 /* set it to 0 if there are no waiters left: */
178 if (likely(list_empty(&lock->wait_list)))
179 atomic_set(&lock->count, 0);
180
181 spin_unlock_mutex(&lock->wait_lock);
182
183 debug_mutex_free_waiter(&waiter);
184
185 DEBUG_WARN_ON(list_empty(&lock->held_list));
186 DEBUG_WARN_ON(lock->owner != task->thread_info);
187
188 return 0;
189 }
190
191 static void fastcall noinline __sched
192 __mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__)
193 {
194 struct mutex *lock = container_of(lock_count, struct mutex, count);
195
196 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE __IP__);
197 }
198
199 /*
200 * Release the lock, slowpath:
201 */
202 static fastcall noinline void
203 __mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__)
204 {
205 struct mutex *lock = container_of(lock_count, struct mutex, count);
206
207 DEBUG_WARN_ON(lock->owner != current_thread_info());
208
209 spin_lock_mutex(&lock->wait_lock);
210
211 /*
212 * some architectures leave the lock unlocked in the fastpath failure
213 * case, others need to leave it locked. In the later case we have to
214 * unlock it here
215 */
216 if (__mutex_slowpath_needs_to_unlock())
217 atomic_set(&lock->count, 1);
218
219 debug_mutex_unlock(lock);
220
221 if (!list_empty(&lock->wait_list)) {
222 /* get the first entry from the wait-list: */
223 struct mutex_waiter *waiter =
224 list_entry(lock->wait_list.next,
225 struct mutex_waiter, list);
226
227 debug_mutex_wake_waiter(lock, waiter);
228
229 wake_up_process(waiter->task);
230 }
231
232 debug_mutex_clear_owner(lock);
233
234 spin_unlock_mutex(&lock->wait_lock);
235 }
236
237 /*
238 * Here come the less common (and hence less performance-critical) APIs:
239 * mutex_lock_interruptible() and mutex_trylock().
240 */
241 static int fastcall noinline __sched
242 __mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__);
243
244 /***
245 * mutex_lock_interruptible - acquire the mutex, interruptable
246 * @lock: the mutex to be acquired
247 *
248 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
249 * been acquired or sleep until the mutex becomes available. If a
250 * signal arrives while waiting for the lock then this function
251 * returns -EINTR.
252 *
253 * This function is similar to (but not equivalent to) down_interruptible().
254 */
255 int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
256 {
257 might_sleep();
258 return __mutex_fastpath_lock_retval
259 (&lock->count, __mutex_lock_interruptible_slowpath);
260 }
261
262 EXPORT_SYMBOL(mutex_lock_interruptible);
263
264 static int fastcall noinline __sched
265 __mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__)
266 {
267 struct mutex *lock = container_of(lock_count, struct mutex, count);
268
269 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE __IP__);
270 }
271
272 /*
273 * Spinlock based trylock, we take the spinlock and check whether we
274 * can get the lock:
275 */
276 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
277 {
278 struct mutex *lock = container_of(lock_count, struct mutex, count);
279 int prev;
280
281 spin_lock_mutex(&lock->wait_lock);
282
283 prev = atomic_xchg(&lock->count, -1);
284 if (likely(prev == 1))
285 debug_mutex_set_owner(lock, current_thread_info() __RET_IP__);
286 /* Set it back to 0 if there are no waiters: */
287 if (likely(list_empty(&lock->wait_list)))
288 atomic_set(&lock->count, 0);
289
290 spin_unlock_mutex(&lock->wait_lock);
291
292 return prev == 1;
293 }
294
295 /***
296 * mutex_trylock - try acquire the mutex, without waiting
297 * @lock: the mutex to be acquired
298 *
299 * Try to acquire the mutex atomically. Returns 1 if the mutex
300 * has been acquired successfully, and 0 on contention.
301 *
302 * NOTE: this function follows the spin_trylock() convention, so
303 * it is negated to the down_trylock() return values! Be careful
304 * about this when converting semaphore users to mutexes.
305 *
306 * This function must not be used in interrupt context. The
307 * mutex must be released by the same task that acquired it.
308 */
309 int fastcall mutex_trylock(struct mutex *lock)
310 {
311 return __mutex_fastpath_trylock(&lock->count,
312 __mutex_trylock_slowpath);
313 }
314
315 EXPORT_SYMBOL(mutex_trylock);
316
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