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         set_current_state(state);
  76         spin_unlock_irqrestore(&q->lock, flags);
  77 }
  78 EXPORT_SYMBOL(prepare_to_wait);
  79
  80 void
  81 prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
  82 {
  83         unsigned long flags;
  84
  85         wait->flags |= WQ_FLAG_EXCLUSIVE;
  86         spin_lock_irqsave(&q->lock, flags);
  87         if (list_empty(&wait->task_list))
  88                 __add_wait_queue_tail(q, wait);
  89         set_current_state(state);
  90         spin_unlock_irqrestore(&q->lock, flags);
  91 }
  92 EXPORT_SYMBOL(prepare_to_wait_exclusive);
  93
  94 void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
  95 {
  96         unsigned long flags;
  97
  98         __set_current_state(TASK_RUNNING);
  99         /*
 100          * We can check for list emptiness outside the lock
 101          * IFF:
 102          *  - we use the "careful" check that verifies both
 103          *    the next and prev pointers, so that there cannot
 104          *    be any half-pending updates in progress on other
 105          *    CPU's that we haven't seen yet (and that might
 106          *    still change the stack area.
 107          * and
 108          *  - all other users take the lock (ie we can only
 109          *    have _one_ other CPU that looks at or modifies
 110          *    the list).
 111          */
 112         if (!list_empty_careful(&wait->task_list)) {
 113                 spin_lock_irqsave(&q->lock, flags);
 114                 list_del_init(&wait->task_list);
 115                 spin_unlock_irqrestore(&q->lock, flags);
 116         }
 117 }
 118 EXPORT_SYMBOL(finish_wait);
 119
 120 int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
 121 {
 122         int ret = default_wake_function(wait, mode, sync, key);
 123
 124         if (ret)
 125                 list_del_init(&wait->task_list);
 126         return ret;
 127 }
 128 EXPORT_SYMBOL(autoremove_wake_function);
 129
 130 int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
 131 {
 132         struct wait_bit_key *key = arg;
 133         struct wait_bit_queue *wait_bit
 134                 = container_of(wait, struct wait_bit_queue, wait);
 135
 136         if (wait_bit->key.flags != key->flags ||
 137                         wait_bit->key.bit_nr != key->bit_nr ||
 138                         test_bit(key->bit_nr, key->flags))
 139                 return 0;
 140         else
 141                 return autoremove_wake_function(wait, mode, sync, key);
 142 }
 143 EXPORT_SYMBOL(wake_bit_function);
 144
 145 /*
 146  * To allow interruptible waiting and asynchronous (i.e. nonblocking)
 147  * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
 148  * permitted return codes. Nonzero return codes halt waiting and return.
 149  */
 150 int __sched
 151 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
 152                         int (*action)(void *), unsigned mode)
 153 {
 154         int ret = 0;
 155
 156         do {
 157                 prepare_to_wait(wq, &q->wait, mode);
 158                 if (test_bit(q->key.bit_nr, q->key.flags))
 159                         ret = (*action)(q->key.flags);
 160         } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
 161         finish_wait(wq, &q->wait);
 162         return ret;
 163 }
 164 EXPORT_SYMBOL(__wait_on_bit);
 165
 166 int __sched out_of_line_wait_on_bit(void *word, int bit,
 167                                         int (*action)(void *), unsigned mode)
 168 {
 169         wait_queue_head_t *wq = bit_waitqueue(word, bit);
 170         DEFINE_WAIT_BIT(wait, word, bit);
 171
 172         return __wait_on_bit(wq, &wait, action, mode);
 173 }
 174 EXPORT_SYMBOL(out_of_line_wait_on_bit);
 175
 176 int __sched
 177 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
 178                         int (*action)(void *), unsigned mode)
 179 {
 180         int ret = 0;
 181
 182         do {
 183                 prepare_to_wait_exclusive(wq, &q->wait, mode);
 184                 if (test_bit(q->key.bit_nr, q->key.flags)) {
 185                         if ((ret = (*action)(q->key.flags)))
 186                                 break;
 187                 }
 188         } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
 189         finish_wait(wq, &q->wait);
 190         return ret;
 191 }
 192 EXPORT_SYMBOL(__wait_on_bit_lock);
 193
 194 int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
 195                                         int (*action)(void *), unsigned mode)
 196 {
 197         wait_queue_head_t *wq = bit_waitqueue(word, bit);
 198         DEFINE_WAIT_BIT(wait, word, bit);
 199
 200         return __wait_on_bit_lock(wq, &wait, action, mode);
 201 }
 202 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
 203
 204 void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
 205 {
 206         struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
 207         if (waitqueue_active(wq))
 208                 __wake_up(wq, TASK_NORMAL, 1, &key);
 209 }
 210 EXPORT_SYMBOL(__wake_up_bit);
 211
 212 /**
 213  * wake_up_bit - wake up a waiter on a bit
 214  * @word: the word being waited on, a kernel virtual address
 215  * @bit: the bit of the word being waited on
 216  *
 217  * There is a standard hashed waitqueue table for generic use. This
 218  * is the part of the hashtable's accessor API that wakes up waiters
 219  * on a bit. For instance, if one were to have waiters on a bitflag,
 220  * one would call wake_up_bit() after clearing the bit.
 221  *
 222  * In order for this to function properly, as it uses waitqueue_active()
 223  * internally, some kind of memory barrier must be done prior to calling
 224  * this. Typically, this will be smp_mb__after_clear_bit(), but in some
 225  * cases where bitflags are manipulated non-atomically under a lock, one
 226  * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
 227  * because spin_unlock() does not guarantee a memory barrier.
 228  */
 229 void wake_up_bit(void *word, int bit)
 230 {
 231         __wake_up_bit(bit_waitqueue(word, bit), word, bit);
 232 }
 233 EXPORT_SYMBOL(wake_up_bit);
 234
 235 wait_queue_head_t *bit_waitqueue(void *word, int bit)
 236 {
 237         const int shift = BITS_PER_LONG == 32 ? 5 : 6;
 238         const struct zone *zone = page_zone(virt_to_page(word));
 239         unsigned long val = (unsigned long)word << shift | bit;
 240
 241         return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
 242 }
 243 EXPORT_SYMBOL(bit_waitqueue);