1/* SPDX-License-Identifier: GPL-2.0 */ 2#ifndef _LINUX_SCHED_WAKE_Q_H 3#define _LINUX_SCHED_WAKE_Q_H 4 5/* 6 * Wake-queues are lists of tasks with a pending wakeup, whose 7 * callers have already marked the task as woken internally, 8 * and can thus carry on. A common use case is being able to 9 * do the wakeups once the corresponding user lock as been 10 * released. 11 * 12 * We hold reference to each task in the list across the wakeup, 13 * thus guaranteeing that the memory is still valid by the time 14 * the actual wakeups are performed in wake_up_q(). 15 * 16 * One per task suffices, because there's never a need for a task to be 17 * in two wake queues simultaneously; it is forbidden to abandon a task 18 * in a wake queue (a call to wake_up_q() _must_ follow), so if a task is 19 * already in a wake queue, the wakeup will happen soon and the second 20 * waker can just skip it. 21 * 22 * The DEFINE_WAKE_Q macro declares and initializes the list head. 23 * wake_up_q() does NOT reinitialize the list; it's expected to be 24 * called near the end of a function. Otherwise, the list can be 25 * re-initialized for later re-use by wake_q_init(). 26 * 27 * Note that this can cause spurious wakeups. schedule() callers 28 * must ensure the call is done inside a loop, confirming that the 29 * wakeup condition has in fact occurred. 30 */ 31 32#include <linux/sched.h> 33 34struct wake_q_head { 35 struct wake_q_node *first; 36 struct wake_q_node **lastp; 37}; 38 39#define WAKE_Q_TAIL ((struct wake_q_node *) 0x01) 40 41#define DEFINE_WAKE_Q(name) \ 42 struct wake_q_head name = { WAKE_Q_TAIL, &name.first } 43 44static inline void wake_q_init(struct wake_q_head *head) 45{ 46 head->first = WAKE_Q_TAIL; 47 head->lastp = &head->first; 48} 49 50extern void wake_q_add(struct wake_q_head *head, 51 struct task_struct *task); 52extern void wake_up_q(struct wake_q_head *head); 53 54#endif /* _LINUX_SCHED_WAKE_Q_H */ 55