/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_RCUWAIT_H_
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#define _LINUX_RCUWAIT_H_
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#include <linux/rcupdate.h>
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/*
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* rcuwait provides a way of blocking and waking up a single
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* task in an rcu-safe manner; where it is forbidden to use
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* after exit_notify(). task_struct is not properly rcu protected,
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* unless dealing with rcu-aware lists, ie: find_task_by_*().
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*
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* Alternatively we have task_rcu_dereference(), but the return
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* semantics have different implications which would break the
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* wakeup side. The only time @task is non-nil is when a user is
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* blocked (or checking if it needs to) on a condition, and reset
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* as soon as we know that the condition has succeeded and are
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* awoken.
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*/
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struct rcuwait {
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struct task_struct *task;
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};
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#define __RCUWAIT_INITIALIZER(name) \
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{ .task = NULL, }
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static inline void rcuwait_init(struct rcuwait *w)
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{
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w->task = NULL;
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}
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extern void rcuwait_wake_up(struct rcuwait *w);
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/*
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* The caller is responsible for locking around rcuwait_wait_event(),
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* such that writes to @task are properly serialized.
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*/
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#define rcuwait_wait_event(w, condition) \
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({ \
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/* \
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* Complain if we are called after do_exit()/exit_notify(), \
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* as we cannot rely on the rcu critical region for the \
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* wakeup side. \
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*/ \
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WARN_ON(current->exit_state); \
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\
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rcu_assign_pointer((w)->task, current); \
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for (;;) { \
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/* \
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* Implicit barrier (A) pairs with (B) in \
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* rcuwait_wake_up(). \
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*/ \
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set_current_state(TASK_UNINTERRUPTIBLE); \
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if (condition) \
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break; \
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\
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schedule(); \
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} \
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\
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WRITE_ONCE((w)->task, NULL); \
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__set_current_state(TASK_RUNNING); \
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})
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#endif /* _LINUX_RCUWAIT_H_ */
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