diff options
Diffstat (limited to 'include/linux/rcuwait.h')
| -rw-r--r-- | include/linux/rcuwait.h | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h new file mode 100644 index 000000000000..a4ede51b3e7c --- /dev/null +++ b/include/linux/rcuwait.h @@ -0,0 +1,63 @@ +#ifndef _LINUX_RCUWAIT_H_ +#define _LINUX_RCUWAIT_H_ + +#include <linux/rcupdate.h> + +/* + * rcuwait provides a way of blocking and waking up a single + * task in an rcu-safe manner; where it is forbidden to use + * after exit_notify(). task_struct is not properly rcu protected, + * unless dealing with rcu-aware lists, ie: find_task_by_*(). + * + * Alternatively we have task_rcu_dereference(), but the return + * semantics have different implications which would break the + * wakeup side. The only time @task is non-nil is when a user is + * blocked (or checking if it needs to) on a condition, and reset + * as soon as we know that the condition has succeeded and are + * awoken. + */ +struct rcuwait { + struct task_struct *task; +}; + +#define __RCUWAIT_INITIALIZER(name) \ + { .task = NULL, } + +static inline void rcuwait_init(struct rcuwait *w) +{ + w->task = NULL; +} + +extern void rcuwait_wake_up(struct rcuwait *w); + +/* + * The caller is responsible for locking around rcuwait_wait_event(), + * such that writes to @task are properly serialized. + */ +#define rcuwait_wait_event(w, condition) \ +({ \ + /* \ + * Complain if we are called after do_exit()/exit_notify(), \ + * as we cannot rely on the rcu critical region for the \ + * wakeup side. \ + */ \ + WARN_ON(current->exit_state); \ + \ + rcu_assign_pointer((w)->task, current); \ + for (;;) { \ + /* \ + * Implicit barrier (A) pairs with (B) in \ + * rcuwait_wake_up(). \ + */ \ + set_current_state(TASK_UNINTERRUPTIBLE); \ + if (condition) \ + break; \ + \ + schedule(); \ + } \ + \ + WRITE_ONCE((w)->task, NULL); \ + __set_current_state(TASK_RUNNING); \ +}) + +#endif /* _LINUX_RCUWAIT_H_ */ |