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