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; where it is forbidden to use 10 * after exit_notify(). task_struct is not properly rcu protected, 11 * unless dealing with rcu-aware lists, ie: find_task_by_*(). 12 * 13 * Alternatively we have task_rcu_dereference(), but the return 14 * semantics have different implications which would break the 15 * wakeup side. The only time @task is non-nil is when a user is 16 * blocked (or checking if it needs to) on a condition, and reset 17 * as soon as we know that the condition has succeeded and are 18 * awoken. 19 */ 20 struct rcuwait { 21 struct task_struct __rcu *task; 22 }; 23 24 #define __RCUWAIT_INITIALIZER(name) \ 25 { .task = NULL, } 26 27 static inline void rcuwait_init(struct rcuwait *w) 28 { 29 w->task = NULL; 30 } 31 32 extern void rcuwait_wake_up(struct rcuwait *w); 33 34 /* 35 * The caller is responsible for locking around rcuwait_wait_event(), 36 * such that writes to @task are properly serialized. 37 */ 38 #define rcuwait_wait_event(w, condition) \ 39 ({ \ 40 /* \ 41 * Complain if we are called after do_exit()/exit_notify(), \ 42 * as we cannot rely on the rcu critical region for the \ 43 * wakeup side. \ 44 */ \ 45 WARN_ON(current->exit_state); \ 46 \ 47 rcu_assign_pointer((w)->task, current); \ 48 for (;;) { \ 49 /* \ 50 * Implicit barrier (A) pairs with (B) in \ 51 * rcuwait_wake_up(). \ 52 */ \ 53 set_current_state(TASK_UNINTERRUPTIBLE); \ 54 if (condition) \ 55 break; \ 56 \ 57 schedule(); \ 58 } \ 59 \ 60 WRITE_ONCE((w)->task, NULL); \ 61 __set_current_state(TASK_RUNNING); \ 62 }) 63 64 #endif /* _LINUX_RCUWAIT_H_ */ 65