linux-kernel - Re: WARNING in task_participate_group

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Message-ID: <20151102180624.GA24361@redhat.com>
Date:	Mon, 2 Nov 2015 19:06:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Roland McGrath <roland@...k.frob.com>,
	Andrew Morton <akpm@...ux-foundation.org>, amanieu@...il.com,
	pmoore@...hat.com, Ingo Molnar <mingo@...nel.org>,
	vdavydov@...allels.com, qiaowei.ren@...el.com, dave@...olabs.net,
	palmer@...belt.com, LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: WARNING in task_participate_group_stop

On 11/02, Oleg Nesterov wrote:
>
> On 11/02, Oleg Nesterov wrote:
> >
> > On 11/02, Dmitry Vyukov wrote:
> > >
> > > But I wasn't able
> > > to figure out what's the root cause (why task does not have
> > > JOBCTL_STOP_PENDING) and maybe the same WARNING can be triggered
> > > without root and/or with other than init process. So still posting it
> > > here.
> >
> > Yes I think you are right. SIGSTOP can race with SIGKILL which (unlike SIGCONT)
> > doesn't clear JOBCTL_STOP_DEQUEUED/PENDING/etc.
>
> I was wrong... I forgot that complete_signal(SIGKILL) sets SIGNAL_GROUP_EXIT.
> Unless SIGNAL_UNKILLABLE is set, and this is what makes init "special".

and I think this should be fixed anyway, if nothing else to make this logic more
correct. I'll try to recheck this all later.

> So it seems that everything is clear. Except I can't understand why your
> test-case doesn't work for me ;) It should.

Damn. Sorry Dmitry it actually works. Just I didn't see the output from
pr_warn()'s on the serial console due to the wrong console_loglevel.

Oleg.

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