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Date: Mon, 2 Nov 2015 17:36:54 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Roland McGrath <roland@hack.frob.com>,
        Andrew Morton <akpm@linux-foundation.org>, amanieu@gmail.com,
        pmoore@redhat.com, Ingo Molnar <mingo@kernel.org>,
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        palmer@dabbelt.com, LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>
Subject: Re: WARNING in task_participate_group_stop
Message-ID: <20151102163654.GA18804@redhat.com>
References: <CACT4Y+bbV2AM-v=T-pikxZX04T=b5Qzc7a2PY4HoakLcKr8RJw@mail.gmail.com> <20151102151333.GA17152@redhat.com>
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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".

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

Oleg.