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 #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
  23 static inline void rcuwait_init(struct rcuwait *w)
  24 {
  25         w->task = NULL;
  26 }
  27
  28 extern void rcuwait_wake_up(struct rcuwait *w);
  29
  30 /*
  31  * The caller is responsible for locking around rcuwait_wait_event(),
  32  * such that writes to @task are properly serialized.
  33  */
  34 #define rcuwait_wait_event(w, condition, state)                         \
  35 ({                                                                      \
  36         int __ret = 0;                                                  \
  37         rcu_assign_pointer((w)->task, current);                         \
  38         for (;;) {                                                      \
  39                 /*                                                      \
  40                  * Implicit barrier (A) pairs with (B) in               \
  41                  * rcuwait_wake_up().                                   \
  42                  */                                                     \
  43                 set_current_state(state);                               \
  44                 if (condition)                                          \
  45                         break;                                          \
  46                                                                         \
  47                 if (signal_pending_state(state, current)) {             \
  48                         __ret = -EINTR;                                 \
  49                         break;                                          \
  50                 }                                                       \
  51                                                                         \
  52                 schedule();                                             \
  53         }                                                               \
  54                                                                         \
  55         WRITE_ONCE((w)->task, NULL);                                    \
  56         __set_current_state(TASK_RUNNING);                              \
  57         __ret;                                                          \
  58 })
  59
  60 #endif /* _LINUX_RCUWAIT_H_ */