include/linux/swait.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_SWAIT_H
   3 #define _LINUX_SWAIT_H
   4
   5 #include <linux/list.h>
   6 #include <linux/stddef.h>
   7 #include <linux/spinlock.h>
   8 #include <asm/current.h>
   9
  10 /*
  11  * Simple wait queues
  12  *
  13  * While these are very similar to the other/complex wait queues (wait.h) the
  14  * most important difference is that the simple waitqueue allows for
  15  * deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold
  16  * times.
  17  *
  18  * In order to make this so, we had to drop a fair number of features of the
  19  * other waitqueue code; notably:
  20  *
  21  *  - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;
  22  *    all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
  23  *    sleeper state.
  24  *
  25  *  - the exclusive mode; because this requires preserving the list order
  26  *    and this is hard.
  27  *
  28  *  - custom wake functions; because you cannot give any guarantees about
  29  *    random code.
  30  *
  31  * As a side effect of this; the data structures are slimmer.
  32  *
  33  * One would recommend using this wait queue where possible.
  34  */
  35
  36 struct task_struct;
  37
  38 struct swait_queue_head {
  39         raw_spinlock_t          lock;
  40         struct list_head        task_list;
  41 };
  42
  43 struct swait_queue {
  44         struct task_struct      *task;
  45         struct list_head        task_list;
  46 };
  47
  48 #define __SWAITQUEUE_INITIALIZER(name) {                                \
  49         .task           = current,                                      \
  50         .task_list      = LIST_HEAD_INIT((name).task_list),             \
  51 }
  52
  53 #define DECLARE_SWAITQUEUE(name)                                        \
  54         struct swait_queue name = __SWAITQUEUE_INITIALIZER(name)
  55
  56 #define __SWAIT_QUEUE_HEAD_INITIALIZER(name) {                          \
  57         .lock           = __RAW_SPIN_LOCK_UNLOCKED(name.lock),          \
  58         .task_list      = LIST_HEAD_INIT((name).task_list),             \
  59 }
  60
  61 #define DECLARE_SWAIT_QUEUE_HEAD(name)                                  \
  62         struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name)
  63
  64 extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name,
  65                                     struct lock_class_key *key);
  66
  67 #define init_swait_queue_head(q)                                \
  68         do {                                                    \
  69                 static struct lock_class_key __key;             \
  70                 __init_swait_queue_head((q), #q, &__key);       \
  71         } while (0)
  72
  73 #ifdef CONFIG_LOCKDEP
  74 # define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)                  \
  75         ({ init_swait_queue_head(&name); name; })
  76 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)                 \
  77         struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)
  78 #else
  79 # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name)                 \
  80         DECLARE_SWAIT_QUEUE_HEAD(name)
  81 #endif
  82
  83 /**
  84  * swait_active -- locklessly test for waiters on the queue
  85  * @wq: the waitqueue to test for waiters
  86  *
  87  * returns true if the wait list is not empty
  88  *
  89  * NOTE: this function is lockless and requires care, incorrect usage _will_
  90  * lead to sporadic and non-obvious failure.
  91  *
  92  * NOTE2: this function has the same above implications as regular waitqueues.
  93  *
  94  * Use either while holding swait_queue_head::lock or when used for wakeups
  95  * with an extra smp_mb() like:
  96  *
  97  *      CPU0 - waker                    CPU1 - waiter
  98  *
  99  *                                      for (;;) {
 100  *      @cond = true;                     prepare_to_swait(&wq_head, &wait, state);
 101  *      smp_mb();                         // smp_mb() from set_current_state()
 102  *      if (swait_active(wq_head))        if (@cond)
 103  *        wake_up(wq_head);                      break;
 104  *                                        schedule();
 105  *                                      }
 106  *                                      finish_swait(&wq_head, &wait);
 107  *
 108  * Because without the explicit smp_mb() it's possible for the
 109  * swait_active() load to get hoisted over the @cond store such that we'll
 110  * observe an empty wait list while the waiter might not observe @cond.
 111  * This, in turn, can trigger missing wakeups.
 112  *
 113  * Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
 114  * which (when the lock is uncontended) are of roughly equal cost.
 115  */
 116 static inline int swait_active(struct swait_queue_head *wq)
 117 {
 118         return !list_empty(&wq->task_list);
 119 }
 120
 121 /**
 122  * swq_has_sleeper - check if there are any waiting processes
 123  * @wq: the waitqueue to test for waiters
 124  *
 125  * Returns true if @wq has waiting processes
 126  *
 127  * Please refer to the comment for swait_active.
 128  */
 129 static inline bool swq_has_sleeper(struct swait_queue_head *wq)
 130 {
 131         /*
 132          * We need to be sure we are in sync with the list_add()
 133          * modifications to the wait queue (task_list).
 134          *
 135          * This memory barrier should be paired with one on the
 136          * waiting side.
 137          */
 138         smp_mb();
 139         return swait_active(wq);
 140 }
 141
 142 extern void swake_up(struct swait_queue_head *q);
 143 extern void swake_up_all(struct swait_queue_head *q);
 144 extern void swake_up_locked(struct swait_queue_head *q);
 145
 146 extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
 147 extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state);
 148 extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);
 149
 150 extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
 151 extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
 152
 153 /* as per ___wait_event() but for swait, therefore "exclusive == 0" */
 154 #define ___swait_event(wq, condition, state, ret, cmd)                  \
 155 ({                                                                      \
 156         struct swait_queue __wait;                                      \
 157         long __ret = ret;                                               \
 158                                                                         \
 159         INIT_LIST_HEAD(&__wait.task_list);                              \
 160         for (;;) {                                                      \
 161                 long __int = prepare_to_swait_event(&wq, &__wait, state);\
 162                                                                         \
 163                 if (condition)                                          \
 164                         break;                                          \
 165                                                                         \
 166                 if (___wait_is_interruptible(state) && __int) {         \
 167                         __ret = __int;                                  \
 168                         break;                                          \
 169                 }                                                       \
 170                                                                         \
 171                 cmd;                                                    \
 172         }                                                               \
 173         finish_swait(&wq, &__wait);                                     \
 174         __ret;                                                          \
 175 })
 176
 177 #define __swait_event(wq, condition)                                    \
 178         (void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0,    \
 179                             schedule())
 180
 181 #define swait_event(wq, condition)                                      \
 182 do {                                                                    \
 183         if (condition)                                                  \
 184                 break;                                                  \
 185         __swait_event(wq, condition);                                   \
 186 } while (0)
 187
 188 #define __swait_event_timeout(wq, condition, timeout)                   \
 189         ___swait_event(wq, ___wait_cond_timeout(condition),             \
 190                       TASK_UNINTERRUPTIBLE, timeout,                    \
 191                       __ret = schedule_timeout(__ret))
 192
 193 #define swait_event_timeout(wq, condition, timeout)                     \
 194 ({                                                                      \
 195         long __ret = timeout;                                           \
 196         if (!___wait_cond_timeout(condition))                           \
 197                 __ret = __swait_event_timeout(wq, condition, timeout);  \
 198         __ret;                                                          \
 199 })
 200
 201 #define __swait_event_interruptible(wq, condition)                      \
 202         ___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0,            \
 203                       schedule())
 204
 205 #define swait_event_interruptible(wq, condition)                        \
 206 ({                                                                      \
 207         int __ret = 0;                                                  \
 208         if (!(condition))                                               \
 209                 __ret = __swait_event_interruptible(wq, condition);     \
 210         __ret;                                                          \
 211 })
 212
 213 #define __swait_event_interruptible_timeout(wq, condition, timeout)     \
 214         ___swait_event(wq, ___wait_cond_timeout(condition),             \
 215                       TASK_INTERRUPTIBLE, timeout,                      \
 216                       __ret = schedule_timeout(__ret))
 217
 218 #define swait_event_interruptible_timeout(wq, condition, timeout)       \
 219 ({                                                                      \
 220         long __ret = timeout;                                           \
 221         if (!___wait_cond_timeout(condition))                           \
 222                 __ret = __swait_event_interruptible_timeout(wq,         \
 223                                                 condition, timeout);    \
 224         __ret;                                                          \
 225 })
 226
 227 #define __swait_event_idle(wq, condition)                               \
 228         (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule())
 229
 230 /**
 231  * swait_event_idle - wait without system load contribution
 232  * @wq: the waitqueue to wait on
 233  * @condition: a C expression for the event to wait for
 234  *
 235  * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
 236  * true. The @condition is checked each time the waitqueue @wq is woken up.
 237  *
 238  * This function is mostly used when a kthread or workqueue waits for some
 239  * condition and doesn't want to contribute to system load. Signals are
 240  * ignored.
 241  */
 242 #define swait_event_idle(wq, condition)                                 \
 243 do {                                                                    \
 244         if (condition)                                                  \
 245                 break;                                                  \
 246         __swait_event_idle(wq, condition);                              \
 247 } while (0)
 248
 249 #define __swait_event_idle_timeout(wq, condition, timeout)              \
 250         ___swait_event(wq, ___wait_cond_timeout(condition),             \
 251                        TASK_IDLE, timeout,                              \
 252                        __ret = schedule_timeout(__ret))
 253
 254 /**
 255  * swait_event_idle_timeout - wait up to timeout without load contribution
 256  * @wq: the waitqueue to wait on
 257  * @condition: a C expression for the event to wait for
 258  * @timeout: timeout at which we'll give up in jiffies
 259  *
 260  * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
 261  * true. The @condition is checked each time the waitqueue @wq is woken up.
 262  *
 263  * This function is mostly used when a kthread or workqueue waits for some
 264  * condition and doesn't want to contribute to system load. Signals are
 265  * ignored.
 266  *
 267  * Returns:
 268  * 0 if the @condition evaluated to %false after the @timeout elapsed,
 269  * 1 if the @condition evaluated to %true after the @timeout elapsed,
 270  * or the remaining jiffies (at least 1) if the @condition evaluated
 271  * to %true before the @timeout elapsed.
 272  */
 273 #define swait_event_idle_timeout(wq, condition, timeout)                \
 274 ({                                                                      \
 275         long __ret = timeout;                                           \
 276         if (!___wait_cond_timeout(condition))                           \
 277                 __ret = __swait_event_idle_timeout(wq,                  \
 278                                                    condition, timeout); \
 279         __ret;                                                          \
 280 })
 281
 282 #endif /* _LINUX_SWAIT_H */