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64 lines
1.8 KiB
64 lines
1.8 KiB
/* 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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