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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 : : * NOTE that there is no guarantee the wakeup will happen any later than the 32 : : * wake_q_add() location. Therefore task must be ready to be woken at the 33 : : * location of the wake_q_add(). 34 : : */ 35 : : 36 : : #include <linux/sched.h> 37 : : 38 : : struct wake_q_head { 39 : : struct wake_q_node *first; 40 : : struct wake_q_node **lastp; 41 : : }; 42 : : 43 : : #define WAKE_Q_TAIL ((struct wake_q_node *) 0x01) 44 : : 45 : : #define DEFINE_WAKE_Q(name) \ 46 : : struct wake_q_head name = { WAKE_Q_TAIL, &name.first } 47 : : 48 : 0 : static inline void wake_q_init(struct wake_q_head *head) 49 : : { 50 : 0 : head->first = WAKE_Q_TAIL; 51 : 0 : head->lastp = &head->first; 52 : : } 53 : : 54 : 3 : static inline bool wake_q_empty(struct wake_q_head *head) 55 : : { 56 [ - + ]: 3 : return head->first == WAKE_Q_TAIL; 57 : : } 58 : : 59 : : extern void wake_q_add(struct wake_q_head *head, struct task_struct *task); 60 : : extern void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task); 61 : : extern void wake_up_q(struct wake_q_head *head); 62 : : 63 : : #endif /* _LINUX_SCHED_WAKE_Q_H */