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TOMOYO Linux Cross Reference
Linux/kernel/wait.c

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  1 /*
  2  * Generic waiting primitives.
  3  *
  4  * (C) 2004 Nadia Yvette Chambers, Oracle
  5  */
  6 #include <linux/init.h>
  7 #include <linux/export.h>
  8 #include <linux/sched.h>
  9 #include <linux/mm.h>
 10 #include <linux/wait.h>
 11 #include <linux/hash.h>
 12 
 13 void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
 14 {
 15         spin_lock_init(&q->lock);
 16         lockdep_set_class_and_name(&q->lock, key, name);
 17         INIT_LIST_HEAD(&q->task_list);
 18 }
 19 
 20 EXPORT_SYMBOL(__init_waitqueue_head);
 21 
 22 void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
 23 {
 24         unsigned long flags;
 25 
 26         wait->flags &= ~WQ_FLAG_EXCLUSIVE;
 27         spin_lock_irqsave(&q->lock, flags);
 28         __add_wait_queue(q, wait);
 29         spin_unlock_irqrestore(&q->lock, flags);
 30 }
 31 EXPORT_SYMBOL(add_wait_queue);
 32 
 33 void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
 34 {
 35         unsigned long flags;
 36 
 37         wait->flags |= WQ_FLAG_EXCLUSIVE;
 38         spin_lock_irqsave(&q->lock, flags);
 39         __add_wait_queue_tail(q, wait);
 40         spin_unlock_irqrestore(&q->lock, flags);
 41 }
 42 EXPORT_SYMBOL(add_wait_queue_exclusive);
 43 
 44 void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
 45 {
 46         unsigned long flags;
 47 
 48         spin_lock_irqsave(&q->lock, flags);
 49         __remove_wait_queue(q, wait);
 50         spin_unlock_irqrestore(&q->lock, flags);
 51 }
 52 EXPORT_SYMBOL(remove_wait_queue);
 53 
 54 
 55 /*
 56  * Note: we use "set_current_state()" _after_ the wait-queue add,
 57  * because we need a memory barrier there on SMP, so that any
 58  * wake-function that tests for the wait-queue being active
 59  * will be guaranteed to see waitqueue addition _or_ subsequent
 60  * tests in this thread will see the wakeup having taken place.
 61  *
 62  * The spin_unlock() itself is semi-permeable and only protects
 63  * one way (it only protects stuff inside the critical region and
 64  * stops them from bleeding out - it would still allow subsequent
 65  * loads to move into the critical region).
 66  */
 67 void
 68 prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
 69 {
 70         unsigned long flags;
 71 
 72         wait->flags &= ~WQ_FLAG_EXCLUSIVE;
 73         spin_lock_irqsave(&q->lock, flags);
 74         if (list_empty(&wait->task_list))
 75                 __add_wait_queue(q, wait);
 76         set_current_state(state);
 77         spin_unlock_irqrestore(&q->lock, flags);
 78 }
 79 EXPORT_SYMBOL(prepare_to_wait);
 80 
 81 void
 82 prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
 83 {
 84         unsigned long flags;
 85 
 86         wait->flags |= WQ_FLAG_EXCLUSIVE;
 87         spin_lock_irqsave(&q->lock, flags);
 88         if (list_empty(&wait->task_list))
 89                 __add_wait_queue_tail(q, wait);
 90         set_current_state(state);
 91         spin_unlock_irqrestore(&q->lock, flags);
 92 }
 93 EXPORT_SYMBOL(prepare_to_wait_exclusive);
 94 
 95 /**
 96  * finish_wait - clean up after waiting in a queue
 97  * @q: waitqueue waited on
 98  * @wait: wait descriptor
 99  *
100  * Sets current thread back to running state and removes
101  * the wait descriptor from the given waitqueue if still
102  * queued.
103  */
104 void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
105 {
106         unsigned long flags;
107 
108         __set_current_state(TASK_RUNNING);
109         /*
110          * We can check for list emptiness outside the lock
111          * IFF:
112          *  - we use the "careful" check that verifies both
113          *    the next and prev pointers, so that there cannot
114          *    be any half-pending updates in progress on other
115          *    CPU's that we haven't seen yet (and that might
116          *    still change the stack area.
117          * and
118          *  - all other users take the lock (ie we can only
119          *    have _one_ other CPU that looks at or modifies
120          *    the list).
121          */
122         if (!list_empty_careful(&wait->task_list)) {
123                 spin_lock_irqsave(&q->lock, flags);
124                 list_del_init(&wait->task_list);
125                 spin_unlock_irqrestore(&q->lock, flags);
126         }
127 }
128 EXPORT_SYMBOL(finish_wait);
129 
130 /**
131  * abort_exclusive_wait - abort exclusive waiting in a queue
132  * @q: waitqueue waited on
133  * @wait: wait descriptor
134  * @mode: runstate of the waiter to be woken
135  * @key: key to identify a wait bit queue or %NULL
136  *
137  * Sets current thread back to running state and removes
138  * the wait descriptor from the given waitqueue if still
139  * queued.
140  *
141  * Wakes up the next waiter if the caller is concurrently
142  * woken up through the queue.
143  *
144  * This prevents waiter starvation where an exclusive waiter
145  * aborts and is woken up concurrently and no one wakes up
146  * the next waiter.
147  */
148 void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
149                         unsigned int mode, void *key)
150 {
151         unsigned long flags;
152 
153         __set_current_state(TASK_RUNNING);
154         spin_lock_irqsave(&q->lock, flags);
155         if (!list_empty(&wait->task_list))
156                 list_del_init(&wait->task_list);
157         else if (waitqueue_active(q))
158                 __wake_up_locked_key(q, mode, key);
159         spin_unlock_irqrestore(&q->lock, flags);
160 }
161 EXPORT_SYMBOL(abort_exclusive_wait);
162 
163 int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
164 {
165         int ret = default_wake_function(wait, mode, sync, key);
166 
167         if (ret)
168                 list_del_init(&wait->task_list);
169         return ret;
170 }
171 EXPORT_SYMBOL(autoremove_wake_function);
172 
173 int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
174 {
175         struct wait_bit_key *key = arg;
176         struct wait_bit_queue *wait_bit
177                 = container_of(wait, struct wait_bit_queue, wait);
178 
179         if (wait_bit->key.flags != key->flags ||
180                         wait_bit->key.bit_nr != key->bit_nr ||
181                         test_bit(key->bit_nr, key->flags))
182                 return 0;
183         else
184                 return autoremove_wake_function(wait, mode, sync, key);
185 }
186 EXPORT_SYMBOL(wake_bit_function);
187 
188 /*
189  * To allow interruptible waiting and asynchronous (i.e. nonblocking)
190  * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
191  * permitted return codes. Nonzero return codes halt waiting and return.
192  */
193 int __sched
194 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
195                         int (*action)(void *), unsigned mode)
196 {
197         int ret = 0;
198 
199         do {
200                 prepare_to_wait(wq, &q->wait, mode);
201                 if (test_bit(q->key.bit_nr, q->key.flags))
202                         ret = (*action)(q->key.flags);
203         } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
204         finish_wait(wq, &q->wait);
205         return ret;
206 }
207 EXPORT_SYMBOL(__wait_on_bit);
208 
209 int __sched out_of_line_wait_on_bit(void *word, int bit,
210                                         int (*action)(void *), unsigned mode)
211 {
212         wait_queue_head_t *wq = bit_waitqueue(word, bit);
213         DEFINE_WAIT_BIT(wait, word, bit);
214 
215         return __wait_on_bit(wq, &wait, action, mode);
216 }
217 EXPORT_SYMBOL(out_of_line_wait_on_bit);
218 
219 int __sched
220 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
221                         int (*action)(void *), unsigned mode)
222 {
223         do {
224                 int ret;
225 
226                 prepare_to_wait_exclusive(wq, &q->wait, mode);
227                 if (!test_bit(q->key.bit_nr, q->key.flags))
228                         continue;
229                 ret = action(q->key.flags);
230                 if (!ret)
231                         continue;
232                 abort_exclusive_wait(wq, &q->wait, mode, &q->key);
233                 return ret;
234         } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
235         finish_wait(wq, &q->wait);
236         return 0;
237 }
238 EXPORT_SYMBOL(__wait_on_bit_lock);
239 
240 int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
241                                         int (*action)(void *), unsigned mode)
242 {
243         wait_queue_head_t *wq = bit_waitqueue(word, bit);
244         DEFINE_WAIT_BIT(wait, word, bit);
245 
246         return __wait_on_bit_lock(wq, &wait, action, mode);
247 }
248 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
249 
250 void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
251 {
252         struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
253         if (waitqueue_active(wq))
254                 __wake_up(wq, TASK_NORMAL, 1, &key);
255 }
256 EXPORT_SYMBOL(__wake_up_bit);
257 
258 /**
259  * wake_up_bit - wake up a waiter on a bit
260  * @word: the word being waited on, a kernel virtual address
261  * @bit: the bit of the word being waited on
262  *
263  * There is a standard hashed waitqueue table for generic use. This
264  * is the part of the hashtable's accessor API that wakes up waiters
265  * on a bit. For instance, if one were to have waiters on a bitflag,
266  * one would call wake_up_bit() after clearing the bit.
267  *
268  * In order for this to function properly, as it uses waitqueue_active()
269  * internally, some kind of memory barrier must be done prior to calling
270  * this. Typically, this will be smp_mb__after_clear_bit(), but in some
271  * cases where bitflags are manipulated non-atomically under a lock, one
272  * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
273  * because spin_unlock() does not guarantee a memory barrier.
274  */
275 void wake_up_bit(void *word, int bit)
276 {
277         __wake_up_bit(bit_waitqueue(word, bit), word, bit);
278 }
279 EXPORT_SYMBOL(wake_up_bit);
280 
281 wait_queue_head_t *bit_waitqueue(void *word, int bit)
282 {
283         const int shift = BITS_PER_LONG == 32 ? 5 : 6;
284         const struct zone *zone = page_zone(virt_to_page(word));
285         unsigned long val = (unsigned long)word << shift | bit;
286 
287         return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
288 }
289 EXPORT_SYMBOL(bit_waitqueue);
290 
291 /*
292  * Manipulate the atomic_t address to produce a better bit waitqueue table hash
293  * index (we're keying off bit -1, but that would produce a horrible hash
294  * value).
295  */
296 static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
297 {
298         if (BITS_PER_LONG == 64) {
299                 unsigned long q = (unsigned long)p;
300                 return bit_waitqueue((void *)(q & ~1), q & 1);
301         }
302         return bit_waitqueue(p, 0);
303 }
304 
305 static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
306                                   void *arg)
307 {
308         struct wait_bit_key *key = arg;
309         struct wait_bit_queue *wait_bit
310                 = container_of(wait, struct wait_bit_queue, wait);
311         atomic_t *val = key->flags;
312 
313         if (wait_bit->key.flags != key->flags ||
314             wait_bit->key.bit_nr != key->bit_nr ||
315             atomic_read(val) != 0)
316                 return 0;
317         return autoremove_wake_function(wait, mode, sync, key);
318 }
319 
320 /*
321  * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
322  * the actions of __wait_on_atomic_t() are permitted return codes.  Nonzero
323  * return codes halt waiting and return.
324  */
325 static __sched
326 int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
327                        int (*action)(atomic_t *), unsigned mode)
328 {
329         atomic_t *val;
330         int ret = 0;
331 
332         do {
333                 prepare_to_wait(wq, &q->wait, mode);
334                 val = q->key.flags;
335                 if (atomic_read(val) == 0)
336                         break;
337                 ret = (*action)(val);
338         } while (!ret && atomic_read(val) != 0);
339         finish_wait(wq, &q->wait);
340         return ret;
341 }
342 
343 #define DEFINE_WAIT_ATOMIC_T(name, p)                                   \
344         struct wait_bit_queue name = {                                  \
345                 .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p),              \
346                 .wait   = {                                             \
347                         .private        = current,                      \
348                         .func           = wake_atomic_t_function,       \
349                         .task_list      =                               \
350                                 LIST_HEAD_INIT((name).wait.task_list),  \
351                 },                                                      \
352         }
353 
354 __sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
355                                          unsigned mode)
356 {
357         wait_queue_head_t *wq = atomic_t_waitqueue(p);
358         DEFINE_WAIT_ATOMIC_T(wait, p);
359 
360         return __wait_on_atomic_t(wq, &wait, action, mode);
361 }
362 EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
363 
364 /**
365  * wake_up_atomic_t - Wake up a waiter on a atomic_t
366  * @p: The atomic_t being waited on, a kernel virtual address
367  *
368  * Wake up anyone waiting for the atomic_t to go to zero.
369  *
370  * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
371  * check is done by the waiter's wake function, not the by the waker itself).
372  */
373 void wake_up_atomic_t(atomic_t *p)
374 {
375         __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
376 }
377 EXPORT_SYMBOL(wake_up_atomic_t);
378 

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