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 WAKE_Q_HEAD_INITIALIZER(name) \ |
46 | { WAKE_Q_TAIL, &name.first } |
47 | |
48 | #define DEFINE_WAKE_Q(name) \ |
49 | struct wake_q_head name = WAKE_Q_HEAD_INITIALIZER(name) |
50 | |
51 | static inline void wake_q_init(struct wake_q_head *head) |
52 | { |
53 | head->first = WAKE_Q_TAIL; |
54 | head->lastp = &head->first; |
55 | } |
56 | |
57 | static inline bool wake_q_empty(struct wake_q_head *head) |
58 | { |
59 | return head->first == WAKE_Q_TAIL; |
60 | } |
61 | |
62 | extern void wake_q_add(struct wake_q_head *head, struct task_struct *task); |
63 | extern void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task); |
64 | extern void wake_up_q(struct wake_q_head *head); |
65 | |
66 | #endif /* _LINUX_SCHED_WAKE_Q_H */ |
67 | |