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- /* SPDX-License-Identifier: GPL-2.0 */
- #ifndef _LINUX_SCHED_WAKE_Q_H
- #define _LINUX_SCHED_WAKE_Q_H
- /*
- * Wake-queues are lists of tasks with a pending wakeup, whose
- * callers have already marked the task as woken internally,
- * and can thus carry on. A common use case is being able to
- * do the wakeups once the corresponding user lock as been
- * released.
- *
- * We hold reference to each task in the list across the wakeup,
- * thus guaranteeing that the memory is still valid by the time
- * the actual wakeups are performed in wake_up_q().
- *
- * One per task suffices, because there's never a need for a task to be
- * in two wake queues simultaneously; it is forbidden to abandon a task
- * in a wake queue (a call to wake_up_q() _must_ follow), so if a task is
- * already in a wake queue, the wakeup will happen soon and the second
- * waker can just skip it.
- *
- * The DEFINE_WAKE_Q macro declares and initializes the list head.
- * wake_up_q() does NOT reinitialize the list; it's expected to be
- * called near the end of a function. Otherwise, the list can be
- * re-initialized for later re-use by wake_q_init().
- *
- * NOTE that this can cause spurious wakeups. schedule() callers
- * must ensure the call is done inside a loop, confirming that the
- * wakeup condition has in fact occurred.
- *
- * NOTE that there is no guarantee the wakeup will happen any later than the
- * wake_q_add() location. Therefore task must be ready to be woken at the
- * location of the wake_q_add().
- */
- #include <linux/sched.h>
- struct wake_q_head {
- struct wake_q_node *first;
- struct wake_q_node **lastp;
- int count;
- };
- #define WAKE_Q_TAIL ((struct wake_q_node *) 0x01)
- #define WAKE_Q_HEAD_INITIALIZER(name) \
- { WAKE_Q_TAIL, &name.first }
- #define DEFINE_WAKE_Q(name) \
- struct wake_q_head name = WAKE_Q_HEAD_INITIALIZER(name)
- static inline void wake_q_init(struct wake_q_head *head)
- {
- head->first = WAKE_Q_TAIL;
- head->lastp = &head->first;
- head->count = 0;
- }
- static inline bool wake_q_empty(struct wake_q_head *head)
- {
- return head->first == WAKE_Q_TAIL;
- }
- extern void wake_q_add(struct wake_q_head *head, struct task_struct *task);
- extern void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task);
- extern void wake_up_q(struct wake_q_head *head);
- #endif /* _LINUX_SCHED_WAKE_Q_H */
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