/* 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; }; #define WAKE_Q_TAIL ((struct wake_q_node *) 0x01) #define DEFINE_WAKE_Q(name) \ struct wake_q_head name = { WAKE_Q_TAIL, &name.first } static inline void wake_q_init(struct wake_q_head *head) { head->first = WAKE_Q_TAIL; head->lastp = &head->first; } extern void wake_q_add(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 */