kernel/wait.c

   1 /*
   2  * Generic waiting primitives.
   3  *
   4  * (C) 2004 William Irwin, Oracle
   5  */
   6 #include <linux/config.h>
   7 #include <linux/init.h>
   8 #include <linux/module.h>
   9 #include <linux/sched.h>
  10 #include <linux/mm.h>
  11 #include <linux/wait.h>
  12 #include <linux/hash.h>
  13
  14 void fastcall add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
  15 {
  16         unsigned long flags;
  17
  18         wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  19         spin_lock_irqsave(&q->lock, flags);
  20         __add_wait_queue(q, wait);
  21         spin_unlock_irqrestore(&q->lock, flags);
  22 }
  23 EXPORT_SYMBOL(add_wait_queue);
  24
  25 void fastcall add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
  26 {
  27         unsigned long flags;
  28
  29         wait->flags |= WQ_FLAG_EXCLUSIVE;
  30         spin_lock_irqsave(&q->lock, flags);
  31         __add_wait_queue_tail(q, wait);
  32         spin_unlock_irqrestore(&q->lock, flags);
  33 }
  34 EXPORT_SYMBOL(add_wait_queue_exclusive);
  35
  36 void fastcall remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
  37 {
  38         unsigned long flags;
  39
  40         spin_lock_irqsave(&q->lock, flags);
  41         __remove_wait_queue(q, wait);
  42         spin_unlock_irqrestore(&q->lock, flags);
  43 }
  44 EXPORT_SYMBOL(remove_wait_queue);
  45
  46
  47 /*
  48  * Note: we use "set_current_state()" _after_ the wait-queue add,
  49  * because we need a memory barrier there on SMP, so that any
  50  * wake-function that tests for the wait-queue being active
  51  * will be guaranteed to see waitqueue addition _or_ subsequent
  52  * tests in this thread will see the wakeup having taken place.
  53  *
  54  * The spin_unlock() itself is semi-permeable and only protects
  55  * one way (it only protects stuff inside the critical region and
  56  * stops them from bleeding out - it would still allow subsequent
  57  * loads to move into the the critical region).
  58  */
  59 void fastcall
  60 prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
  61 {
  62         unsigned long flags;
  63
  64         wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  65         spin_lock_irqsave(&q->lock, flags);
  66         if (list_empty(&wait->task_list))
  67                 __add_wait_queue(q, wait);
  68         /*
  69          * don't alter the task state if this is just going to
  70          * queue an async wait queue callback
  71          */
  72         if (is_sync_wait(wait))
  73                 set_current_state(state);
  74         spin_unlock_irqrestore(&q->lock, flags);
  75 }
  76 EXPORT_SYMBOL(prepare_to_wait);
  77
  78 void fastcall
  79 prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
  80 {
  81         unsigned long flags;
  82
  83         wait->flags |= WQ_FLAG_EXCLUSIVE;
  84         spin_lock_irqsave(&q->lock, flags);
  85         if (list_empty(&wait->task_list))
  86                 __add_wait_queue_tail(q, wait);
  87         /*
  88          * don't alter the task state if this is just going to
  89          * queue an async wait queue callback
  90          */
  91         if (is_sync_wait(wait))
  92                 set_current_state(state);
  93         spin_unlock_irqrestore(&q->lock, flags);
  94 }
  95 EXPORT_SYMBOL(prepare_to_wait_exclusive);
  96
  97 void fastcall finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
  98 {
  99         unsigned long flags;
 100
 101         __set_current_state(TASK_RUNNING);
 102         /*
 103          * We can check for list emptiness outside the lock
 104          * IFF:
 105          *  - we use the "careful" check that verifies both
 106          *    the next and prev pointers, so that there cannot
 107          *    be any half-pending updates in progress on other
 108          *    CPU's that we haven't seen yet (and that might
 109          *    still change the stack area.
 110          * and
 111          *  - all other users take the lock (ie we can only
 112          *    have _one_ other CPU that looks at or modifies
 113          *    the list).
 114          */
 115         if (!list_empty_careful(&wait->task_list)) {
 116                 spin_lock_irqsave(&q->lock, flags);
 117                 list_del_init(&wait->task_list);
 118                 spin_unlock_irqrestore(&q->lock, flags);
 119         }
 120 }
 121 EXPORT_SYMBOL(finish_wait);
 122
 123 int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
 124 {
 125         int ret = default_wake_function(wait, mode, sync, key);
 126
 127         if (ret)
 128                 list_del_init(&wait->task_list);
 129         return ret;
 130 }
 131 EXPORT_SYMBOL(autoremove_wake_function);
 132
 133 int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
 134 {
 135         struct wait_bit_key *key = arg;
 136         struct wait_bit_queue *wait_bit
 137                 = container_of(wait, struct wait_bit_queue, wait);
 138
 139         if (wait_bit->key.flags != key->flags ||
 140                         wait_bit->key.bit_nr != key->bit_nr ||
 141                         test_bit(key->bit_nr, key->flags))
 142                 return 0;
 143         else
 144                 return autoremove_wake_function(wait, mode, sync, key);
 145 }
 146 EXPORT_SYMBOL(wake_bit_function);
 147
 148 /*
 149  * To allow interruptible waiting and asynchronous (i.e. nonblocking)
 150  * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
 151  * permitted return codes. Nonzero return codes halt waiting and return.
 152  */
 153 int __sched fastcall
 154 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
 155                         int (*action)(void *), unsigned mode)
 156 {
 157         int ret = 0;
 158
 159         do {
 160                 prepare_to_wait(wq, &q->wait, mode);
 161                 if (test_bit(q->key.bit_nr, q->key.flags))
 162                         ret = (*action)(q->key.flags);
 163         } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
 164         finish_wait(wq, &q->wait);
 165         return ret;
 166 }
 167 EXPORT_SYMBOL(__wait_on_bit);
 168
 169 int __sched fastcall out_of_line_wait_on_bit(void *word, int bit,
 170                                         int (*action)(void *), unsigned mode)
 171 {
 172         wait_queue_head_t *wq = bit_waitqueue(word, bit);
 173         DEFINE_WAIT_BIT(wait, word, bit);
 174
 175         return __wait_on_bit(wq, &wait, action, mode);
 176 }
 177 EXPORT_SYMBOL(out_of_line_wait_on_bit);
 178
 179 int __sched fastcall
 180 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
 181                         int (*action)(void *), unsigned mode)
 182 {
 183         int ret = 0;
 184
 185         do {
 186                 prepare_to_wait_exclusive(wq, &q->wait, mode);
 187                 if (test_bit(q->key.bit_nr, q->key.flags)) {
 188                         if ((ret = (*action)(q->key.flags)))
 189                                 break;
 190                 }
 191         } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
 192         finish_wait(wq, &q->wait);
 193         return ret;
 194 }
 195 EXPORT_SYMBOL(__wait_on_bit_lock);
 196
 197 int __sched fastcall out_of_line_wait_on_bit_lock(void *word, int bit,
 198                                         int (*action)(void *), unsigned mode)
 199 {
 200         wait_queue_head_t *wq = bit_waitqueue(word, bit);
 201         DEFINE_WAIT_BIT(wait, word, bit);
 202
 203         return __wait_on_bit_lock(wq, &wait, action, mode);
 204 }
 205 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
 206
 207 void fastcall __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
 208 {
 209         struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
 210         if (waitqueue_active(wq))
 211                 __wake_up(wq, TASK_INTERRUPTIBLE|TASK_UNINTERRUPTIBLE, 1, &key);
 212 }
 213 EXPORT_SYMBOL(__wake_up_bit);
 214
 215 /**
 216  * wake_up_bit - wake up a waiter on a bit
 217  * @word: the word being waited on, a kernel virtual address
 218  * @bit: the bit of the word being waited on
 219  *
 220  * There is a standard hashed waitqueue table for generic use. This
 221  * is the part of the hashtable's accessor API that wakes up waiters
 222  * on a bit. For instance, if one were to have waiters on a bitflag,
 223  * one would call wake_up_bit() after clearing the bit.
 224  *
 225  * In order for this to function properly, as it uses waitqueue_active()
 226  * internally, some kind of memory barrier must be done prior to calling
 227  * this. Typically, this will be smp_mb__after_clear_bit(), but in some
 228  * cases where bitflags are manipulated non-atomically under a lock, one
 229  * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
 230  * because spin_unlock() does not guarantee a memory barrier.
 231  */
 232 void fastcall wake_up_bit(void *word, int bit)
 233 {
 234         __wake_up_bit(bit_waitqueue(word, bit), word, bit);
 235 }
 236 EXPORT_SYMBOL(wake_up_bit);
 237
 238 fastcall wait_queue_head_t *bit_waitqueue(void *word, int bit)
 239 {
 240         const int shift = BITS_PER_LONG == 32 ? 5 : 6;
 241         const struct zone *zone = page_zone(virt_to_page(word));
 242         unsigned long val = (unsigned long)word << shift | bit;
 243
 244         return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
 245 }
 246 EXPORT_SYMBOL(bit_waitqueue);