Commit f31e11d8 authored Aug 20, 2008 by Oleg Nesterov Committed by Ingo Molnar Aug 22, 2008

wait_task_inactive(): don't consider task->nivcsw



If wait_task_inactive() returns success the task was deactivated.  In that
case schedule() always increments ->nvcsw which alone can be used as a
"generation counter".

If the next call returns the same number, we can be sure that the task was
unscheduled.  Otherwise, because we know that .on_rq == 0 again, ->nvcsw
should have been changed in between.

Q: perhaps it is better to do "ncsw = (p->nvcsw << 1) | 1" ?  This
decreases the possibility of "was it unscheduled" false positive when
->nvcsw == 0.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 94d3d824

kernel/sched.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -1921,11 +1921,8 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state)
		running = task_running(rq, p);
		on_rq = p->se.on_rq;
		ncsw = 0;
		if (!match_state \|\| p->state == match_state) {
		ncsw = p->nivcsw + p->nvcsw;
		if (unlikely(!ncsw))
		ncsw = 1;
		}
		if (!match_state \|\| p->state == match_state)
		ncsw = p->nvcsw ?: 1;
		task_rq_unlock(rq, &flags);

		/*

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