include/linux/rcuwait.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_RCUWAIT_H_
   3 #define _LINUX_RCUWAIT_H_
   4
   5 #include <linux/rcupdate.h>
   6
   7 /*
   8  * rcuwait provides a way of blocking and waking up a single
   9  * task in an rcu-safe manner.
  10  *
  11  * The only time @task is non-nil is when a user is blocked (or
  12  * checking if it needs to) on a condition, and reset as soon as we
  13  * know that the condition has succeeded and are awoken.
  14  */
  15 struct rcuwait {
  16         struct task_struct __rcu *task;
  17 };
  18
  19 #define __RCUWAIT_INITIALIZER(name)             \
  20         { .task = NULL, }
  21
  22 static inline void rcuwait_init(struct rcuwait *w)
  23 {
  24         w->task = NULL;
  25 }
  26
  27 extern void rcuwait_wake_up(struct rcuwait *w);
  28
  29 /*
  30  * The caller is responsible for locking around rcuwait_wait_event(),
  31  * such that writes to @task are properly serialized.
  32  */
  33 #define rcuwait_wait_event(w, condition)                                \
  34 ({                                                                      \
  35         rcu_assign_pointer((w)->task, current);                         \
  36         for (;;) {                                                      \
  37                 /*                                                      \
  38                  * Implicit barrier (A) pairs with (B) in               \
  39                  * rcuwait_wake_up().                                   \
  40                  */                                                     \
  41                 set_current_state(TASK_UNINTERRUPTIBLE);                \
  42                 if (condition)                                          \
  43                         break;                                          \
  44                                                                         \
  45                 schedule();                                             \
  46         }                                                               \
  47                                                                         \
  48         WRITE_ONCE((w)->task, NULL);                                    \
  49         __set_current_state(TASK_RUNNING);                              \
  50 })
  51
  52 #endif /* _LINUX_RCUWAIT_H_ */