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