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- /* SPDX-License-Identifier: GPL-2.0 */
- #ifndef _LINUX_SWAIT_H
- #define _LINUX_SWAIT_H
- #include <linux/list.h>
- #include <linux/stddef.h>
- #include <linux/spinlock.h>
- #include <linux/wait.h>
- #include <asm/current.h>
- /*
- * Simple waitqueues are semantically very different to regular wait queues
- * (wait.h). The most important difference is that the simple waitqueue allows
- * for deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold
- * times.
- *
- * Mainly, this is accomplished by two things. Firstly not allowing swake_up_all
- * from IRQ disabled, and dropping the lock upon every wakeup, giving a higher
- * priority task a chance to run.
- *
- * Secondly, we had to drop a fair number of features of the other waitqueue
- * code; notably:
- *
- * - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue;
- * all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right
- * sleeper state.
- *
- * - the !exclusive mode; because that leads to O(n) wakeups, everything is
- * exclusive. As such swake_up_one will only ever awake _one_ waiter.
- *
- * - custom wake callback functions; because you cannot give any guarantees
- * about random code. This also allows swait to be used in RT, such that
- * raw spinlock can be used for the swait queue head.
- *
- * As a side effect of these; the data structures are slimmer albeit more ad-hoc.
- * For all the above, note that simple wait queues should _only_ be used under
- * very specific realtime constraints -- it is best to stick with the regular
- * wait queues in most cases.
- */
- struct task_struct;
- struct swait_queue_head {
- raw_spinlock_t lock;
- struct list_head task_list;
- };
- struct swait_queue {
- struct task_struct *task;
- struct list_head task_list;
- };
- #define __SWAITQUEUE_INITIALIZER(name) { \
- .task = current, \
- .task_list = LIST_HEAD_INIT((name).task_list), \
- }
- #define DECLARE_SWAITQUEUE(name) \
- struct swait_queue name = __SWAITQUEUE_INITIALIZER(name)
- #define __SWAIT_QUEUE_HEAD_INITIALIZER(name) { \
- .lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \
- .task_list = LIST_HEAD_INIT((name).task_list), \
- }
- #define DECLARE_SWAIT_QUEUE_HEAD(name) \
- struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INITIALIZER(name)
- extern void __init_swait_queue_head(struct swait_queue_head *q, const char *name,
- struct lock_class_key *key);
- #define init_swait_queue_head(q) \
- do { \
- static struct lock_class_key __key; \
- __init_swait_queue_head((q), #q, &__key); \
- } while (0)
- #ifdef CONFIG_LOCKDEP
- # define __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name) \
- ({ init_swait_queue_head(&name); name; })
- # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \
- struct swait_queue_head name = __SWAIT_QUEUE_HEAD_INIT_ONSTACK(name)
- #else
- # define DECLARE_SWAIT_QUEUE_HEAD_ONSTACK(name) \
- DECLARE_SWAIT_QUEUE_HEAD(name)
- #endif
- /**
- * swait_active -- locklessly test for waiters on the queue
- * @wq: the waitqueue to test for waiters
- *
- * returns true if the wait list is not empty
- *
- * NOTE: this function is lockless and requires care, incorrect usage _will_
- * lead to sporadic and non-obvious failure.
- *
- * NOTE2: this function has the same above implications as regular waitqueues.
- *
- * Use either while holding swait_queue_head::lock or when used for wakeups
- * with an extra smp_mb() like:
- *
- * CPU0 - waker CPU1 - waiter
- *
- * for (;;) {
- * @cond = true; prepare_to_swait_exclusive(&wq_head, &wait, state);
- * smp_mb(); // smp_mb() from set_current_state()
- * if (swait_active(wq_head)) if (@cond)
- * wake_up(wq_head); break;
- * schedule();
- * }
- * finish_swait(&wq_head, &wait);
- *
- * Because without the explicit smp_mb() it's possible for the
- * swait_active() load to get hoisted over the @cond store such that we'll
- * observe an empty wait list while the waiter might not observe @cond.
- * This, in turn, can trigger missing wakeups.
- *
- * Also note that this 'optimization' trades a spin_lock() for an smp_mb(),
- * which (when the lock is uncontended) are of roughly equal cost.
- */
- static inline int swait_active(struct swait_queue_head *wq)
- {
- return !list_empty(&wq->task_list);
- }
- /**
- * swq_has_sleeper - check if there are any waiting processes
- * @wq: the waitqueue to test for waiters
- *
- * Returns true if @wq has waiting processes
- *
- * Please refer to the comment for swait_active.
- */
- static inline bool swq_has_sleeper(struct swait_queue_head *wq)
- {
- /*
- * We need to be sure we are in sync with the list_add()
- * modifications to the wait queue (task_list).
- *
- * This memory barrier should be paired with one on the
- * waiting side.
- */
- smp_mb();
- return swait_active(wq);
- }
- extern void swake_up_one(struct swait_queue_head *q);
- extern void swake_up_all(struct swait_queue_head *q);
- extern void swake_up_locked(struct swait_queue_head *q);
- extern void prepare_to_swait_exclusive(struct swait_queue_head *q, struct swait_queue *wait, int state);
- extern long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state);
- extern void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
- extern void finish_swait(struct swait_queue_head *q, struct swait_queue *wait);
- /* as per ___wait_event() but for swait, therefore "exclusive == 1" */
- #define ___swait_event(wq, condition, state, ret, cmd) \
- ({ \
- __label__ __out; \
- struct swait_queue __wait; \
- long __ret = ret; \
- \
- INIT_LIST_HEAD(&__wait.task_list); \
- for (;;) { \
- long __int = prepare_to_swait_event(&wq, &__wait, state);\
- \
- if (condition) \
- break; \
- \
- if (___wait_is_interruptible(state) && __int) { \
- __ret = __int; \
- goto __out; \
- } \
- \
- cmd; \
- } \
- finish_swait(&wq, &__wait); \
- __out: __ret; \
- })
- #define __swait_event(wq, condition) \
- (void)___swait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, \
- schedule())
- #define swait_event_exclusive(wq, condition) \
- do { \
- if (condition) \
- break; \
- __swait_event(wq, condition); \
- } while (0)
- #define __swait_event_timeout(wq, condition, timeout) \
- ___swait_event(wq, ___wait_cond_timeout(condition), \
- TASK_UNINTERRUPTIBLE, timeout, \
- __ret = schedule_timeout(__ret))
- #define swait_event_timeout_exclusive(wq, condition, timeout) \
- ({ \
- long __ret = timeout; \
- if (!___wait_cond_timeout(condition)) \
- __ret = __swait_event_timeout(wq, condition, timeout); \
- __ret; \
- })
- #define __swait_event_interruptible(wq, condition) \
- ___swait_event(wq, condition, TASK_INTERRUPTIBLE, 0, \
- schedule())
- #define swait_event_interruptible_exclusive(wq, condition) \
- ({ \
- int __ret = 0; \
- if (!(condition)) \
- __ret = __swait_event_interruptible(wq, condition); \
- __ret; \
- })
- #define __swait_event_interruptible_timeout(wq, condition, timeout) \
- ___swait_event(wq, ___wait_cond_timeout(condition), \
- TASK_INTERRUPTIBLE, timeout, \
- __ret = schedule_timeout(__ret))
- #define swait_event_interruptible_timeout_exclusive(wq, condition, timeout)\
- ({ \
- long __ret = timeout; \
- if (!___wait_cond_timeout(condition)) \
- __ret = __swait_event_interruptible_timeout(wq, \
- condition, timeout); \
- __ret; \
- })
- #define __swait_event_idle(wq, condition) \
- (void)___swait_event(wq, condition, TASK_IDLE, 0, schedule())
- /**
- * swait_event_idle_exclusive - wait without system load contribution
- * @wq: the waitqueue to wait on
- * @condition: a C expression for the event to wait for
- *
- * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
- * true. The @condition is checked each time the waitqueue @wq is woken up.
- *
- * This function is mostly used when a kthread or workqueue waits for some
- * condition and doesn't want to contribute to system load. Signals are
- * ignored.
- */
- #define swait_event_idle_exclusive(wq, condition) \
- do { \
- if (condition) \
- break; \
- __swait_event_idle(wq, condition); \
- } while (0)
- #define __swait_event_idle_timeout(wq, condition, timeout) \
- ___swait_event(wq, ___wait_cond_timeout(condition), \
- TASK_IDLE, timeout, \
- __ret = schedule_timeout(__ret))
- /**
- * swait_event_idle_timeout_exclusive - wait up to timeout without load contribution
- * @wq: the waitqueue to wait on
- * @condition: a C expression for the event to wait for
- * @timeout: timeout at which we'll give up in jiffies
- *
- * The process is put to sleep (TASK_IDLE) until the @condition evaluates to
- * true. The @condition is checked each time the waitqueue @wq is woken up.
- *
- * This function is mostly used when a kthread or workqueue waits for some
- * condition and doesn't want to contribute to system load. Signals are
- * ignored.
- *
- * Returns:
- * 0 if the @condition evaluated to %false after the @timeout elapsed,
- * 1 if the @condition evaluated to %true after the @timeout elapsed,
- * or the remaining jiffies (at least 1) if the @condition evaluated
- * to %true before the @timeout elapsed.
- */
- #define swait_event_idle_timeout_exclusive(wq, condition, timeout) \
- ({ \
- long __ret = timeout; \
- if (!___wait_cond_timeout(condition)) \
- __ret = __swait_event_idle_timeout(wq, \
- condition, timeout); \
- __ret; \
- })
- #endif /* _LINUX_SWAIT_H */
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