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 rcuwait_init(struct rcuwait * w)22static 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_ */ 53