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/* SPDX-License-Identifier: GPL-2.0 */
#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 __rcu *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_ */
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