Release 4.12 include/linux/rcuwait.h

#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;
}

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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_ */
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Directory: include/linux

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