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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#include <linux/sched/signal.h>
7
8/*
9 * rcuwait provides a way of blocking and waking up a single
10 * task in an rcu-safe manner.
11 *
12 * The only time @task is non-nil is when a user is blocked (or
13 * checking if it needs to) on a condition, and reset as soon as we
14 * know that the condition has succeeded and are awoken.
15 */
16struct rcuwait {
17 struct task_struct __rcu *task;
18};
19
20#define __RCUWAIT_INITIALIZER(name) \
21 { .task = NULL, }
22
23static inline void rcuwait_init(struct rcuwait *w)
24{
25 w->task = NULL;
26}
27
28extern void rcuwait_wake_up(struct rcuwait *w);
29
30/*
31 * The caller is responsible for locking around rcuwait_wait_event(),
32 * such that writes to @task are properly serialized.
33 */
34#define rcuwait_wait_event(w, condition, state) \
35({ \
36 int __ret = 0; \
37 rcu_assign_pointer((w)->task, current); \
38 for (;;) { \
39 /* \
40 * Implicit barrier (A) pairs with (B) in \
41 * rcuwait_wake_up(). \
42 */ \
43 set_current_state(state); \
44 if (condition) \
45 break; \
46 \
47 if (signal_pending_state(state, current)) { \
48 __ret = -EINTR; \
49 break; \
50 } \
51 \
52 schedule(); \
53 } \
54 \
55 WRITE_ONCE((w)->task, NULL); \
56 __set_current_state(TASK_RUNNING); \
57 __ret; \
58})
59
60#endif /* _LINUX_RCUWAIT_H_ */