linux-kernel - Re: [PATCH -mm v2 1/3] mm/oom_kill: remove the wrong fatal_signal_pending() check in oom_kill

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Message-ID: <20151001154115.GA10342@redhat.com>
Date:	Thu, 1 Oct 2015 17:41:15 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Kyle Walker <kwalker@...hat.com>,
	Stanislav Kozina <skozina@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v2 1/3] mm/oom_kill: remove the wrong
	fatal_signal_pending() check in oom_kill_process()

On 10/01, Michal Hocko wrote:
>
> On Thu 01-10-15 17:00:10, Oleg Nesterov wrote:
> > On 10/01, Michal Hocko wrote:
> > >
> > > On Wed 30-09-15 20:24:05, Oleg Nesterov wrote:
> > > [...]
> > > > It is possible that the group leader
> > > > has the pending SIGKILL because its sub-thread originated the coredump,
> > > > in this case we must not skip this process.
> > >
> > > I do not understand this. If the group leader has SIGKILL pending it
> > > will die anyway regardless whether we send another sigkill or not, no?
> >
> > Yes it will die, but only after the coredump is finished.
> >
> > Suppose we have a thread group with the group leader P and another
> > thread T. If T starts the coredump, it sends SIGKILL to P and waits
> > until it parks in exit_mm(). Then T actually dumps the core which may
> > need more memory, a lot of time, etc.
> >
> > We need to kill this process. Yes, P is already killed and it sleeps
> > in TASK_UNINTERRUPTIBLE so this thread does not need SIGKILL. But
> > do_send_sig_info(P) will also find T and kill it too to make
> > dump_interrupted() == T.
>
> I am still utterly confused :( Where do we kill T if it is not in the
> same thread group with P?

But it is in the same thread group?

Oleg.

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