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

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Date:	Thu, 26 Jan 2012 16:21:30 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Hiroyuki KAMEZAWA <kamezawa.hiroyu@...fujitsu.com>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] TASK_DEAD task is able to be woken up in special condition

2012/1/25 Peter Zijlstra <peterz@...radead.org>:
> On Wed, 2011-12-28 at 16:07 -0500, KOSAKI Motohiro wrote:
>>
>> CPU0                    CPU1
>> --------------------------------------------------------
>> deactivate_task()
>>                         task->state = TASK_UNINTERRUPTIBLE;
>> activate_task()
>>    rq->nr_uninterruptible--;
>>
>>                         schedule()
>>                           deactivate_task()
>>                             rq->nr_uninterruptible++;
>>
>>
>
> Hmm, I think you're right, when CPU0 does __sched_setscheduler() on the
> task running on CPU1 and CPU1's @task is current.
>
> I think only __sched_setscheduler() is really a problem, the other
> activate/deactivate users not schedule or wakeup are __migrate_task()
> and normalize_task().
>
> __migrate_task() will only run on tasks that aren't actually running
> anywhere so the above scenario can't happen, normalize_task() is never
> used on normal systems (sysrq-n).
>
> So I guess the below cures things and cleans up a bit.. no?

Sorry for the delay. Yeah, I think this should work. (even though I
don't understand __migrate_task() detail)

Thank you!

Ack-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
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