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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_RCUWAIT_H_
3#define _LINUX_RCUWAIT_H_
4
5#include <linux/rcupdate.h>
6
7/*
8 * rcuwait provides a way of blocking and waking up a single
9 * task in an rcu-safe manner.
10 *
11 * The only time @task is non-nil is when a user is blocked (or
12 * checking if it needs to) on a condition, and reset as soon as we
13 * know that the condition has succeeded and are awoken.
14 */
15struct rcuwait {
16 struct task_struct __rcu *task;
17};
18
19#define __RCUWAIT_INITIALIZER(name) \
20 { .task = NULL, }
21
22static inline void rcuwait_init(struct rcuwait *w)
23{
24 w->task = NULL;
25}
26
27extern void rcuwait_wake_up(struct rcuwait *w);
28
29/*
30 * The caller is responsible for locking around rcuwait_wait_event(),
31 * such that writes to @task are properly serialized.
32 */
33#define rcuwait_wait_event(w, condition) \
34({ \
35 rcu_assign_pointer((w)->task, current); \
36 for (;;) { \
37 /* \
38 * Implicit barrier (A) pairs with (B) in \
39 * rcuwait_wake_up(). \
40 */ \
41 set_current_state(TASK_UNINTERRUPTIBLE); \
42 if (condition) \
43 break; \
44 \
45 schedule(); \
46 } \
47 \
48 WRITE_ONCE((w)->task, NULL); \
49 __set_current_state(TASK_RUNNING); \
50})
51
52#endif /* _LINUX_RCUWAIT_H_ */