1 #ifndef _LINUX_RCUWAIT_H_ 2 #define _LINUX_RCUWAIT_H_ 3 4 #include <linux/rcupdate.h> 5 6 /* 7 * rcuwait provides a way of blocking and waking up a single 8 * task in an rcu-safe manner; where it is forbidden to use 9 * after exit_notify(). task_struct is not properly rcu protected, 10 * unless dealing with rcu-aware lists, ie: find_task_by_*(). 11 * 12 * Alternatively we have task_rcu_dereference(), but the return 13 * semantics have different implications which would break the 14 * wakeup side. The only time @task is non-nil is when a user is 15 * blocked (or checking if it needs to) on a condition, and reset 16 * as soon as we know that the condition has succeeded and are 17 * awoken. 18 */ 19 struct rcuwait { 20 struct task_struct *task; 21 }; 22 23 #define __RCUWAIT_INITIALIZER(name) \ 24 { .task = NULL, } 25 26 static inline void rcuwait_init(struct rcuwait *w) 27 { 28 w->task = NULL; 29 } 30 31 extern void rcuwait_wake_up(struct rcuwait *w); 32 33 /* 34 * The caller is responsible for locking around rcuwait_wait_event(), 35 * such that writes to @task are properly serialized. 36 */ 37 #define rcuwait_wait_event(w, condition) \ 38 ({ \ 39 /* \ 40 * Complain if we are called after do_exit()/exit_notify(), \ 41 * as we cannot rely on the rcu critical region for the \ 42 * wakeup side. \ 43 */ \ 44 WARN_ON(current->exit_state); \ 45 \ 46 rcu_assign_pointer((w)->task, current); \ 47 for (;;) { \ 48 /* \ 49 * Implicit barrier (A) pairs with (B) in \ 50 * rcuwait_wake_up(). \ 51 */ \ 52 set_current_state(TASK_UNINTERRUPTIBLE); \ 53 if (condition) \ 54 break; \ 55 \ 56 schedule(); \ 57 } \ 58 \ 59 WRITE_ONCE((w)->task, NULL); \ 60 __set_current_state(TASK_RUNNING); \ 61 }) 62 63 #endif /* _LINUX_RCUWAIT_H_ */ 64