kernel/wait.c

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