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 
50 extern void finish_rcuwait(struct rcuwait *w);
51 
52 #define rcuwait_wait_event(w, condition, state)				\
53 ({									\
54 	int __ret = 0;							\
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 		schedule();						\
71 	}								\
72 	finish_rcuwait(w);						\
73 	__ret;								\
74 })
75 
76 #endif /* _LINUX_RCUWAIT_H_ */
77