Re: [BUG] TASK_DEAD task is able to be woken up in special condition

Peter Zijlstra
2012-01-24T10:24:01Z

On Wed, 2011-12-28 at 16:07 -0500, KOSAKI Motohiro wrote:
> I looked at scheduler code today briefly. now I'm afraid following code
> have similar race.
>
>
> if (task_contributes_to_load(p))
> rq->nr_uninterruptible--;
>
>
>
> Can't following schenario be happen?
>
>
> CPU0 CPU1
> --------------------------------------------------------
> deactivate_task()
> task->state = TASK_UNINTERRUPTIBLE;
> activate_task()
> rq->nr_uninterruptible--;
>
> schedule()
> deactivate_task()
> rq->nr_uninterruptible++;
>
> Totally, nr_uninterruptible wasn't incremented.
>
>
> I'm still not sure. I need to read more sched code.

You shouldn't ever set another tasks ->state.