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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   */
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