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 */
16 struct rcuwait {
17 struct task_struct __rcu *task;
18 };
19
20 #define __RCUWAIT_INITIALIZER(name) \
21 { .task = NULL, }
22
rcuwait_init(struct rcuwait * w)23 static 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 */
rcuwait_active(struct rcuwait * w)32 static inline int rcuwait_active(struct rcuwait *w)
33 {
34 return !!rcu_access_pointer(w->task);
35 }
36
37 extern 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
prepare_to_rcuwait(struct rcuwait * w)45 static inline void prepare_to_rcuwait(struct rcuwait *w)
46 {
47 rcu_assign_pointer(w->task, current);
48 }
49
finish_rcuwait(struct rcuwait * w)50 static inline void finish_rcuwait(struct rcuwait *w)
51 {
52 rcu_assign_pointer(w->task, NULL);
53 __set_current_state(TASK_RUNNING);
54 }
55
56 #define rcuwait_wait_event(w, condition, state) \
57 ({ \
58 int __ret = 0; \
59 prepare_to_rcuwait(w); \
60 for (;;) { \
61 /* \
62 * Implicit barrier (A) pairs with (B) in \
63 * rcuwait_wake_up(). \
64 */ \
65 set_current_state(state); \
66 if (condition) \
67 break; \
68 \
69 if (signal_pending_state(state, current)) { \
70 __ret = -EINTR; \
71 break; \
72 } \
73 \
74 schedule(); \
75 } \
76 finish_rcuwait(w); \
77 __ret; \
78 })
79
80 #endif /* _LINUX_RCUWAIT_H_ */
81