include/linux/swait.h

   1 #ifndef _LINUX_SWAIT_H
   2 #define _LINUX_SWAIT_H
   3
   4 #include <linux/list.h>
   5 #include <linux/stddef.h>
   6 #include <linux/spinlock.h>
   7 #include <asm/current.h>
   8
   9 /*
  10  * Simple wait queues
  11  *
  12  * While these are very similar to the other/complex wait queues (wait.h) the
  13  * most important difference is that the simple waitqueue allows for
  14  * deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold
  15  * times.
  16  *
  17  * In order to make this so, we had to drop a fair number of features of the
  18  * other waitqueue code; notably:
  19  *
  20  *  - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;
  21  *    all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
  22  *    sleeper state.
  23  *
  24  *  - the exclusive mode; because this requires preserving the list order
  25  *    and this is hard.
  26  *
  27  *  - custom wake functions; because you cannot give any guarantees about
  28  *    random code.
  29  *
  30  * As a side effect of this; the data structures are slimmer.
  31  *
  32  * One would recommend using this wait queue where possible.
  33  */
  34
  35 struct task_struct;
  36
  37 struct swait_queue_head {
  38         raw_spinlock_t          lock;
  39         struct list_head        task_list;
  40 };
  41
  42 struct swait_queue {
  43         struct task_struct      *task;
  44         struct list_head        task_list;
  45 };
  46
  47 #define __SWAITQUEUE_INITIALIZER(name) {                                \
  48         .task           = current,                                      \
  49         .task_list      = LIST_HEAD_INIT((name).task_list),             \
  50 }
  51
  52 #define DECLARE_SWAITQUEUE(name)                                        \
  53         struct swait_queue name = __SWAITQUEUE_INITIALIZER(name)
  54
  55 #define __SWAIT_QUEUE_HEAD_INITIALIZER(name) {                          \
  56         .lock           = __RAW_SPIN_LOCK_UNLOCKED(name.lock),          \
  57         .task_list      = LIST_HEAD_INIT((name).task_list),             \
  58 }
  59
  60 #define DECLARE_SWAIT_QUEUE_HEAD(name)                                  \
  61         struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name)
  62
  63 extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name,
  64                                     struct lock_class_key *key);
  65
  66 #define init_swait_queue_head(q)                                \
  67         do {                                                    \
  68                 static struct lock_class_key __key;             \
  69                 __init_swait_queue_head((q), #q, &__key);       \
  70         } while (0)
  71
  72 #ifdef CONFIG_LOCKDEP
  73 # define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)                  \
  74         ({ init_swait_queue_head(&name); name; })
  75 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)                 \
  76         struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)
  77 #else
  78 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)                 \
  79         DECLARE_SWAIT_QUEUE_HEAD(name)
  80 #endif
  81
  82 /**
  83  * swait_active -- locklessly test for waiters on the queue
  84  * @wq: the waitqueue to test for waiters
  85  *
  86  * returns true if the wait list is not empty
  87  *
  88  * NOTE: this function is lockless and requires care, incorrect usage _will_
  89  * lead to sporadic and non-obvious failure.
  90  *
  91  * NOTE2: this function has the same above implications as regular waitqueues.
  92  *
  93  * Use either while holding swait_queue_head::lock or when used for wakeups
  94  * with an extra smp_mb() like:
  95  *
  96  *      CPU0 - waker                    CPU1 - waiter
  97  *
  98  *                                      for (;;) {
  99  *      @cond = true;                     prepare_to_swait(&wq_head, &wait, state);
 100  *      smp_mb();                         // smp_mb() from set_current_state()
 101  *      if (swait_active(wq_head))        if (@cond)
 102  *        wake_up(wq_head);                      break;
 103  *                                        schedule();
 104  *                                      }
 105  *                                      finish_swait(&wq_head, &wait);
 106  *
 107  * Because without the explicit smp_mb() it's possible for the
 108  * swait_active() load to get hoisted over the @cond store such that we'll
 109  * observe an empty wait list while the waiter might not observe @cond.
 110  * This, in turn, can trigger missing wakeups.
 111  *
 112  * Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
 113  * which (when the lock is uncontended) are of roughly equal cost.
 114  */
 115 static inline int swait_active(struct swait_queue_head *wq)
 116 {
 117         return !list_empty(&wq->task_list);
 118 }
 119
 120 /**
 121  * swq_has_sleeper - check if there are any waiting processes
 122  * @wq: the waitqueue to test for waiters
 123  *
 124  * Returns true if @wq has waiting processes
 125  *
 126  * Please refer to the comment for swait_active.
 127  */
 128 static inline bool swq_has_sleeper(struct swait_queue_head *wq)
 129 {
 130         /*
 131          * We need to be sure we are in sync with the list_add()
 132          * modifications to the wait queue (task_list).
 133          *
 134          * This memory barrier should be paired with one on the
 135          * waiting side.
 136          */
 137         smp_mb();
 138         return swait_active(wq);
 139 }
 140
 141 extern void swake_up(struct swait_queue_head *q);
 142 extern void swake_up_all(struct swait_queue_head *q);
 143 extern void swake_up_locked(struct swait_queue_head *q);
 144
 145 extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
 146 extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state);
 147 extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);
 148
 149 extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
 150 extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
 151
 152 /* as per ___wait_event() but for swait, therefore "exclusive == 0" */
 153 #define ___swait_event(wq, condition, state, ret, cmd)                  \
 154 ({                                                                      \
 155         struct swait_queue __wait;                                      \
 156         long __ret = ret;                                               \
 157                                                                         \
 158         INIT_LIST_HEAD(&__wait.task_list);                              \
 159         for (;;) {                                                      \
 160                 long __int = prepare_to_swait_event(&wq, &__wait, state);\
 161                                                                         \
 162                 if (condition)                                          \
 163                         break;                                          \
 164                                                                         \
 165                 if (___wait_is_interruptible(state) && __int) {         \
 166                         __ret = __int;                                  \
 167                         break;                                          \
 168                 }                                                       \
 169                                                                         \
 170                 cmd;                                                    \
 171         }                                                               \
 172         finish_swait(&wq, &__wait);                                     \
 173         __ret;                                                          \
 174 })
 175
 176 #define __swait_event(wq, condition)                                    \
 177         (void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0,    \
 178                             schedule())
 179
 180 #define swait_event(wq, condition)                                      \
 181 do {                                                                    \
 182         if (condition)                                                  \
 183                 break;                                                  \
 184         __swait_event(wq, condition);                                   \
 185 } while (0)
 186
 187 #define __swait_event_timeout(wq, condition, timeout)                   \
 188         ___swait_event(wq, ___wait_cond_timeout(condition),             \
 189                       TASK_UNINTERRUPTIBLE, timeout,                    \
 190                       __ret = schedule_timeout(__ret))
 191
 192 #define swait_event_timeout(wq, condition, timeout)                     \
 193 ({                                                                      \
 194         long __ret = timeout;                                           \
 195         if (!___wait_cond_timeout(condition))                           \
 196                 __ret = __swait_event_timeout(wq, condition, timeout);  \
 197         __ret;                                                          \
 198 })
 199
 200 #define __swait_event_interruptible(wq, condition)                      \
 201         ___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0,            \
 202                       schedule())
 203
 204 #define swait_event_interruptible(wq, condition)                        \
 205 ({                                                                      \
 206         int __ret = 0;                                                  \
 207         if (!(condition))                                               \
 208                 __ret = __swait_event_interruptible(wq, condition);     \
 209         __ret;                                                          \
 210 })
 211
 212 #define __swait_event_interruptible_timeout(wq, condition, timeout)     \
 213         ___swait_event(wq, ___wait_cond_timeout(condition),             \
 214                       TASK_INTERRUPTIBLE, timeout,                      \
 215                       __ret = schedule_timeout(__ret))
 216
 217 #define swait_event_interruptible_timeout(wq, condition, timeout)       \
 218 ({                                                                      \
 219         long __ret = timeout;                                           \
 220         if (!___wait_cond_timeout(condition))                           \
 221                 __ret = __swait_event_interruptible_timeout(wq,         \
 222                                                 condition, timeout);    \
 223         __ret;                                                          \
 224 })
 225
 226 #define __swait_event_idle(wq, condition)                               \
 227         (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule())
 228
 229 /**
 230  * swait_event_idle - wait without system load contribution
 231  * @wq: the waitqueue to wait on
 232  * @condition: a C expression for the event to wait for
 233  *
 234  * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
 235  * true. The @condition is checked each time the waitqueue @wq is woken up.
 236  *
 237  * This function is mostly used when a kthread or workqueue waits for some
 238  * condition and doesn't want to contribute to system load. Signals are
 239  * ignored.
 240  */
 241 #define swait_event_idle(wq, condition)                                 \
 242 do {                                                                    \
 243         if (condition)                                                  \
 244                 break;                                                  \
 245         __swait_event_idle(wq, condition);                              \
 246 } while (0)
 247
 248 #define __swait_event_idle_timeout(wq, condition, timeout)              \
 249         ___swait_event(wq, ___wait_cond_timeout(condition),             \
 250                        TASK_IDLE, timeout,                              \
 251                        __ret = schedule_timeout(__ret))
 252
 253 /**
 254  * swait_event_idle_timeout - wait up to timeout without load contribution
 255  * @wq: the waitqueue to wait on
 256  * @condition: a C expression for the event to wait for
 257  * @timeout: timeout at which we'll give up in jiffies
 258  *
 259  * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
 260  * true. The @condition is checked each time the waitqueue @wq is woken up.
 261  *
 262  * This function is mostly used when a kthread or workqueue waits for some
 263  * condition and doesn't want to contribute to system load. Signals are
 264  * ignored.
 265  *
 266  * Returns:
 267  * 0 if the @condition evaluated to %false after the @timeout elapsed,
 268  * 1 if the @condition evaluated to %true after the @timeout elapsed,
 269  * or the remaining jiffies (at least 1) if the @condition evaluated
 270  * to %true before the @timeout elapsed.
 271  */
 272 #define swait_event_idle_timeout(wq, condition, timeout)                \
 273 ({                                                                      \
 274         long __ret = timeout;                                           \
 275         if (!___wait_cond_timeout(condition))                           \
 276                 __ret = __swait_event_idle_timeout(wq,                  \
 277                                                    condition, timeout); \
 278         __ret;                                                          \
 279 })
 280
 281 #endif /* _LINUX_SWAIT_H */