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[linux-2.6/mini2440.git] / kernel / mutex.c
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1 /*
2 * kernel/mutex.c
4 * Mutexes: blocking mutual exclusion locks
6 * Started by Ingo Molnar:
8 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
10 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
11 * David Howells for suggestions and improvements.
13 * Also see Documentation/mutex-design.txt.
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 #include <linux/debug_locks.h>
23 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
24 * which forces all calls into the slowpath:
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
34 /***
35 * mutex_init - initialize the mutex
36 * @lock: the mutex to be initialized
38 * Initialize the mutex to unlocked state.
40 * It is not allowed to initialize an already locked mutex.
42 void
43 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
45 atomic_set(&lock->count, 1);
46 spin_lock_init(&lock->wait_lock);
47 INIT_LIST_HEAD(&lock->wait_list);
49 debug_mutex_init(lock, name, key);
52 EXPORT_SYMBOL(__mutex_init);
54 #ifndef CONFIG_DEBUG_LOCK_ALLOC
56 * We split the mutex lock/unlock logic into separate fastpath and
57 * slowpath functions, to reduce the register pressure on the fastpath.
58 * We also put the fastpath first in the kernel image, to make sure the
59 * branch is predicted by the CPU as default-untaken.
61 static void fastcall noinline __sched
62 __mutex_lock_slowpath(atomic_t *lock_count);
64 /***
65 * mutex_lock - acquire the mutex
66 * @lock: the mutex to be acquired
68 * Lock the mutex exclusively for this task. If the mutex is not
69 * available right now, it will sleep until it can get it.
71 * The mutex must later on be released by the same task that
72 * acquired it. Recursive locking is not allowed. The task
73 * may not exit without first unlocking the mutex. Also, kernel
74 * memory where the mutex resides mutex must not be freed with
75 * the mutex still locked. The mutex must first be initialized
76 * (or statically defined) before it can be locked. memset()-ing
77 * the mutex to 0 is not allowed.
79 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
80 * checks that will enforce the restrictions and will also do
81 * deadlock debugging. )
83 * This function is similar to (but not equivalent to) down().
85 void inline fastcall __sched mutex_lock(struct mutex *lock)
87 might_sleep();
89 * The locking fastpath is the 1->0 transition from
90 * 'unlocked' into 'locked' state.
92 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
95 EXPORT_SYMBOL(mutex_lock);
96 #endif
98 static void fastcall noinline __sched
99 __mutex_unlock_slowpath(atomic_t *lock_count);
101 /***
102 * mutex_unlock - release the mutex
103 * @lock: the mutex to be released
105 * Unlock a mutex that has been locked by this task previously.
107 * This function must not be used in interrupt context. Unlocking
108 * of a not locked mutex is not allowed.
110 * This function is similar to (but not equivalent to) up().
112 void fastcall __sched mutex_unlock(struct mutex *lock)
115 * The unlocking fastpath is the 0->1 transition from 'locked'
116 * into 'unlocked' state:
118 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
121 EXPORT_SYMBOL(mutex_unlock);
124 * Lock a mutex (possibly interruptible), slowpath:
126 static inline int __sched
127 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
128 unsigned long ip)
130 struct task_struct *task = current;
131 struct mutex_waiter waiter;
132 unsigned int old_val;
133 unsigned long flags;
135 spin_lock_mutex(&lock->wait_lock, flags);
137 debug_mutex_lock_common(lock, &waiter);
138 mutex_acquire(&lock->dep_map, subclass, 0, ip);
139 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
141 /* add waiting tasks to the end of the waitqueue (FIFO): */
142 list_add_tail(&waiter.list, &lock->wait_list);
143 waiter.task = task;
145 old_val = atomic_xchg(&lock->count, -1);
146 if (old_val == 1)
147 goto done;
149 lock_contended(&lock->dep_map, ip);
151 for (;;) {
153 * Lets try to take the lock again - this is needed even if
154 * we get here for the first time (shortly after failing to
155 * acquire the lock), to make sure that we get a wakeup once
156 * it's unlocked. Later on, if we sleep, this is the
157 * operation that gives us the lock. We xchg it to -1, so
158 * that when we release the lock, we properly wake up the
159 * other waiters:
161 old_val = atomic_xchg(&lock->count, -1);
162 if (old_val == 1)
163 break;
166 * got a signal? (This code gets eliminated in the
167 * TASK_UNINTERRUPTIBLE case.)
169 if (unlikely((state == TASK_INTERRUPTIBLE &&
170 signal_pending(task)) ||
171 (state == TASK_KILLABLE &&
172 fatal_signal_pending(task)))) {
173 mutex_remove_waiter(lock, &waiter,
174 task_thread_info(task));
175 mutex_release(&lock->dep_map, 1, ip);
176 spin_unlock_mutex(&lock->wait_lock, flags);
178 debug_mutex_free_waiter(&waiter);
179 return -EINTR;
181 __set_task_state(task, state);
183 /* didnt get the lock, go to sleep: */
184 spin_unlock_mutex(&lock->wait_lock, flags);
185 schedule();
186 spin_lock_mutex(&lock->wait_lock, flags);
189 done:
190 lock_acquired(&lock->dep_map);
191 /* got the lock - rejoice! */
192 mutex_remove_waiter(lock, &waiter, task_thread_info(task));
193 debug_mutex_set_owner(lock, task_thread_info(task));
195 /* set it to 0 if there are no waiters left: */
196 if (likely(list_empty(&lock->wait_list)))
197 atomic_set(&lock->count, 0);
199 spin_unlock_mutex(&lock->wait_lock, flags);
201 debug_mutex_free_waiter(&waiter);
203 return 0;
206 #ifdef CONFIG_DEBUG_LOCK_ALLOC
207 void __sched
208 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
210 might_sleep();
211 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_);
214 EXPORT_SYMBOL_GPL(mutex_lock_nested);
216 int __sched
217 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
219 might_sleep();
220 return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_);
222 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
224 int __sched
225 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
227 might_sleep();
228 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_);
231 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
232 #endif
235 * Release the lock, slowpath:
237 static fastcall inline void
238 __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
240 struct mutex *lock = container_of(lock_count, struct mutex, count);
241 unsigned long flags;
243 spin_lock_mutex(&lock->wait_lock, flags);
244 mutex_release(&lock->dep_map, nested, _RET_IP_);
245 debug_mutex_unlock(lock);
248 * some architectures leave the lock unlocked in the fastpath failure
249 * case, others need to leave it locked. In the later case we have to
250 * unlock it here
252 if (__mutex_slowpath_needs_to_unlock())
253 atomic_set(&lock->count, 1);
255 if (!list_empty(&lock->wait_list)) {
256 /* get the first entry from the wait-list: */
257 struct mutex_waiter *waiter =
258 list_entry(lock->wait_list.next,
259 struct mutex_waiter, list);
261 debug_mutex_wake_waiter(lock, waiter);
263 wake_up_process(waiter->task);
266 debug_mutex_clear_owner(lock);
268 spin_unlock_mutex(&lock->wait_lock, flags);
272 * Release the lock, slowpath:
274 static fastcall noinline void
275 __mutex_unlock_slowpath(atomic_t *lock_count)
277 __mutex_unlock_common_slowpath(lock_count, 1);
280 #ifndef CONFIG_DEBUG_LOCK_ALLOC
282 * Here come the less common (and hence less performance-critical) APIs:
283 * mutex_lock_interruptible() and mutex_trylock().
285 static int fastcall noinline __sched
286 __mutex_lock_killable_slowpath(atomic_t *lock_count);
288 static noinline int fastcall __sched
289 __mutex_lock_interruptible_slowpath(atomic_t *lock_count);
291 /***
292 * mutex_lock_interruptible - acquire the mutex, interruptable
293 * @lock: the mutex to be acquired
295 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
296 * been acquired or sleep until the mutex becomes available. If a
297 * signal arrives while waiting for the lock then this function
298 * returns -EINTR.
300 * This function is similar to (but not equivalent to) down_interruptible().
302 int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
304 might_sleep();
305 return __mutex_fastpath_lock_retval
306 (&lock->count, __mutex_lock_interruptible_slowpath);
309 EXPORT_SYMBOL(mutex_lock_interruptible);
311 int fastcall __sched mutex_lock_killable(struct mutex *lock)
313 might_sleep();
314 return __mutex_fastpath_lock_retval
315 (&lock->count, __mutex_lock_killable_slowpath);
317 EXPORT_SYMBOL(mutex_lock_killable);
319 static void fastcall noinline __sched
320 __mutex_lock_slowpath(atomic_t *lock_count)
322 struct mutex *lock = container_of(lock_count, struct mutex, count);
324 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_);
327 static int fastcall noinline __sched
328 __mutex_lock_killable_slowpath(atomic_t *lock_count)
330 struct mutex *lock = container_of(lock_count, struct mutex, count);
332 return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_);
335 static noinline int fastcall __sched
336 __mutex_lock_interruptible_slowpath(atomic_t *lock_count)
338 struct mutex *lock = container_of(lock_count, struct mutex, count);
340 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);
342 #endif
345 * Spinlock based trylock, we take the spinlock and check whether we
346 * can get the lock:
348 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
350 struct mutex *lock = container_of(lock_count, struct mutex, count);
351 unsigned long flags;
352 int prev;
354 spin_lock_mutex(&lock->wait_lock, flags);
356 prev = atomic_xchg(&lock->count, -1);
357 if (likely(prev == 1)) {
358 debug_mutex_set_owner(lock, current_thread_info());
359 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
361 /* Set it back to 0 if there are no waiters: */
362 if (likely(list_empty(&lock->wait_list)))
363 atomic_set(&lock->count, 0);
365 spin_unlock_mutex(&lock->wait_lock, flags);
367 return prev == 1;
370 /***
371 * mutex_trylock - try acquire the mutex, without waiting
372 * @lock: the mutex to be acquired
374 * Try to acquire the mutex atomically. Returns 1 if the mutex
375 * has been acquired successfully, and 0 on contention.
377 * NOTE: this function follows the spin_trylock() convention, so
378 * it is negated to the down_trylock() return values! Be careful
379 * about this when converting semaphore users to mutexes.
381 * This function must not be used in interrupt context. The
382 * mutex must be released by the same task that acquired it.
384 int fastcall __sched mutex_trylock(struct mutex *lock)
386 return __mutex_fastpath_trylock(&lock->count,
387 __mutex_trylock_slowpath);
390 EXPORT_SYMBOL(mutex_trylock);