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Eric W. Biederman
154abafc68
Remove work arounds that were written before there was a grace period after tasks left the runqueue in finish_task_switch(). In particular now that there tasks exiting the runqueue exprience a RCU grace period none of the work performed by task_rcu_dereference() excpet the rcu_dereference() is necessary so replace task_rcu_dereference() with rcu_dereference(). Remove the code in rcuwait_wait_event() that checks to ensure the current task has not exited. It is no longer necessary as it is guaranteed that any running task will experience a RCU grace period after it leaves the run queueue. Remove the comment in rcuwait_wake_up() as it is no longer relevant. Ref:8f95c90ceb("sched/wait, RCU: Introduce rcuwait machinery") Ref:150593bf86("sched/api: Introduce task_rcu_dereference() and try_get_task_struct()") Signed-off-by: Eric W. Biederman <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Kirill Tkhai <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Russell King - ARM Linux admin <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]>
53 lines
1.2 KiB
C
53 lines
1.2 KiB
C
/* 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.
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*
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* The only time @task is non-nil is when a user is blocked (or
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* checking if it needs to) on a condition, and reset as soon as we
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* know that the condition has succeeded and are awoken.
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*/
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struct rcuwait {
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struct task_struct __rcu *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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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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