From: Mike Galbraith <efault@gmx.de>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: peterz@infradead.org, kosaki.motohiro@gmail.com, oleg@redhat.com,
y-goto@jp.fujitsu.com, mingo@elte.hu,
kamezawa.hiroyu@jp.fujitsu.com, linux-kernel@vger.kernel.org
Subject: Re: [BUG] TASK_DEAD task is able to be woken up in special condition
Date: Wed, 25 Jan 2012 07:15:17 +0100 [thread overview]
Message-ID: <1327472117.7591.12.camel@marge.simson.net> (raw)
In-Reply-To: <4F1EF1E8.4090909@jp.fujitsu.com>
On Tue, 2012-01-24 at 13:01 -0500, KOSAKI Motohiro wrote:
> On 1/24/2012 5:23 AM, Peter Zijlstra wrote:
> > 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.
>
> I'm sorry. I haven't catch your point. I think following step is
> valid kernel code. Do you disagree?
>
> >> task->state = TASK_UNINTERRUPTIBLE;
> >> schedule()
I think you meant:
__set_current_state(TASK_UNINTERRUPTIBLE);
schedule();
The way you wrote it, task doesn't have to be current, so could be doing
the bad thing Peter pointed out, diddling *another* tasks ->state.
-Mike
next prev parent reply other threads:[~2012-01-25 6:15 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-22 0:42 Yasunori Goto
2011-12-22 2:14 ` KOSAKI Motohiro
2011-12-22 8:22 ` Yasunori Goto
2011-12-22 20:02 ` KOSAKI Motohiro
2011-12-23 9:49 ` Peter Zijlstra
2011-12-23 15:41 ` Oleg Nesterov
2011-12-26 8:23 ` Yasunori Goto
2011-12-26 17:11 ` Oleg Nesterov
2011-12-27 6:48 ` Yasunori Goto
2012-01-06 10:22 ` Yasunori Goto
2012-01-06 11:01 ` Peter Zijlstra
2012-01-06 12:01 ` Yasunori Goto
2012-01-06 12:43 ` Peter Zijlstra
2012-01-06 14:12 ` Oleg Nesterov
2012-01-06 14:19 ` Oleg Nesterov
2012-01-07 1:31 ` Yasunori Goto
2012-01-16 11:51 ` Yasunori Goto
2012-01-16 13:38 ` Peter Zijlstra
2012-01-17 8:40 ` Yasunori Goto
2012-01-17 9:06 ` Ingo Molnar
2012-01-17 15:12 ` Oleg Nesterov
2012-01-18 9:42 ` Ingo Molnar
2012-01-18 14:20 ` Oleg Nesterov
2012-01-24 10:19 ` Peter Zijlstra
2012-01-24 10:55 ` Peter Zijlstra
2012-01-24 17:25 ` KOSAKI Motohiro
2012-01-25 15:45 ` Oleg Nesterov
2012-01-25 16:51 ` Peter Zijlstra
2012-01-25 17:43 ` Oleg Nesterov
2012-01-26 15:32 ` Peter Zijlstra
2012-01-26 16:26 ` Oleg Nesterov
2012-01-27 8:59 ` Peter Zijlstra
2012-01-24 10:11 ` Peter Zijlstra
2012-01-26 9:39 ` Ingo Molnar
2012-01-28 12:03 ` [tip:sched/core] sched: Fix ancient race in do_exit() tip-bot for Yasunori Goto
2012-01-28 21:12 ` Linus Torvalds
2012-01-29 16:07 ` Oleg Nesterov
2012-01-29 17:44 ` Linus Torvalds
2012-01-29 18:28 ` Linus Torvalds
2012-01-29 18:59 ` Oleg Nesterov
2012-01-30 16:27 ` Linus Torvalds
2012-01-06 13:48 ` [BUG] TASK_DEAD task is able to be woken up in special condition Oleg Nesterov
2011-12-28 21:07 ` KOSAKI Motohiro
2012-01-24 10:23 ` Peter Zijlstra
2012-01-24 18:01 ` KOSAKI Motohiro
2012-01-25 6:15 ` Mike Galbraith [this message]
2012-01-26 21:24 ` KOSAKI Motohiro
2012-01-25 10:10 ` Peter Zijlstra
2012-01-26 20:25 ` [tip:sched/urgent] sched: Fix rq->nr_uninterruptible update race tip-bot for Peter Zijlstra
2012-01-27 5:20 ` Rakib Mullick
2012-01-27 8:19 ` Peter Zijlstra
2012-01-27 14:11 ` Rakib Mullick
2012-01-26 21:21 ` [BUG] TASK_DEAD task is able to be woken up in special condition KOSAKI Motohiro
2012-01-27 8:21 ` Peter Zijlstra
2011-12-26 6:52 ` Yasunori Goto
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