On Wed, Jun 25, 2014 at 10:00:22PM -0400, Steven Rostedt wrote:
> On Thu, Jun 26, 2014 at 02:43:56AM +0200, Thomas Gleixner wrote:
> >
> > Subject: kthread: Plug park/ unplug race
> > From: Thomas Gleixner <t...@linutronix.de>
> > Date: Thu, 26 Jun 2014 01:24:36 +0200
> >
> > The kthread park/unpark logic has the following issue:
> >
> > Task CPU 0 CPU 1
> >
> > T1 unplug cpu1
> > kthread_park(T2)
> > set_bit(KTHREAD_SHOULD_PARK);
> > wait_for_completion()
> > T2 parkme(X)
>
> But with your patch, isn't it possible for T1 to call thread_unpark here?
Let me answer that.... No, it can't.
I missed the wait_for_completion() above, which will prevent this from
happening.
Nevermind, I'll go work on something less brain intensive.
-- Steve
>
> Then looking at the code I see this turn of events:
>
> if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
> __kthread_bind(k, kthread->cpu, TASK_PARKED);
>
> Which in __kthread_bind() (state == TASK_PARKED)
>
> if (!wait_task_inactive(p, state)) {
> WARN_ON(1);
> return;
> }
>
> Where wait_task_inactive() does:
>
> while (task_running(rq, p)) {
> if (match_state && unlikely(p->state != match_state))
> return 0;
>
> As match_state is non zero and p->state != match_state because it hasn't been
> set yet. The wait_task_inactive() returns zero, and then we hit the WARN_ON()
> in __kthread_bind().
>
> -- Steve
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
