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b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
84f001e1 IM |
2 | #ifndef _LINUX_SCHED_WAKE_Q_H |
3 | #define _LINUX_SCHED_WAKE_Q_H | |
4 | ||
eb61baf6 IM |
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 | * | |
e6018c0f | 27 | * NOTE that this can cause spurious wakeups. schedule() callers |
eb61baf6 IM |
28 | * must ensure the call is done inside a loop, confirming that the |
29 | * wakeup condition has in fact occurred. | |
e6018c0f PZ |
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(). | |
eb61baf6 IM |
34 | */ |
35 | ||
84f001e1 IM |
36 | #include <linux/sched.h> |
37 | ||
eb61baf6 IM |
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 | static inline void wake_q_init(struct wake_q_head *head) | |
49 | { | |
50 | head->first = WAKE_Q_TAIL; | |
51 | head->lastp = &head->first; | |
52 | } | |
53 | ||
54 | extern void wake_q_add(struct wake_q_head *head, | |
55 | struct task_struct *task); | |
56 | extern void wake_up_q(struct wake_q_head *head); | |
57 | ||
84f001e1 | 58 | #endif /* _LINUX_SCHED_WAKE_Q_H */ |