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
28/*
29 * Note: this provides no serialization and, just as with waitqueues,
30 * requires care to estimate as to whether or not the wait is active.
31 */
32static inline int rcuwait_active(struct rcuwait *w)
33{
34	return !!rcu_access_pointer(w->task);
35}
36
37extern int rcuwait_wake_up(struct rcuwait *w);
38
39/*
40 * The caller is responsible for locking around rcuwait_wait_event(),
41 * and [prepare_to/finish]_rcuwait() such that writes to @task are
42 * properly serialized.
43 */
44
45static inline void prepare_to_rcuwait(struct rcuwait *w)
46{
47	rcu_assign_pointer(w->task, current);
48}
49
50extern void finish_rcuwait(struct rcuwait *w);
51
52#define ___rcuwait_wait_event(w, condition, state, ret, cmd)		\
53({									\
54	long __ret = ret;						\
55	prepare_to_rcuwait(w);						\
56	for (;;) {							\
57		/*							\
58		 * Implicit barrier (A) pairs with (B) in		\
59		 * rcuwait_wake_up().					\
60		 */							\
61		set_current_state(state);				\
62		if (condition)						\
63			break;						\
64									\
65		if (signal_pending_state(state, current)) {		\
66			__ret = -EINTR;					\
67			break;						\
68		}							\
69									\
70		cmd;							\
71	}								\
72	finish_rcuwait(w);						\
73	__ret;								\
74})
75
76#define rcuwait_wait_event(w, condition, state)				\
77	___rcuwait_wait_event(w, condition, state, 0, schedule())
78
79#define __rcuwait_wait_event_timeout(w, condition, state, timeout)	\
80	___rcuwait_wait_event(w, ___wait_cond_timeout(condition),	\
81			      state, timeout,				\
82			      __ret = schedule_timeout(__ret))
83
84#define rcuwait_wait_event_timeout(w, condition, state, timeout)	\
85({									\
86	long __ret = timeout;						\
87	if (!___wait_cond_timeout(condition))				\
88		__ret = __rcuwait_wait_event_timeout(w, condition,	\
89						     state, timeout);	\
90	__ret;								\
91})
92
93#endif /* _LINUX_RCUWAIT_H_ */
94