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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>
This commit is contained in:
Oleg Nesterov 2008-08-20 16:54:44 -07:00 committed by Ingo Molnar
parent 94d3d8247d
commit f31e11d87a
1 changed files with 2 additions and 5 deletions
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7
kernel/sched.c
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@ -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);
/*