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