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: <201510022336.IFF00059.OFFLOHJFtVSMQO@I-love.SAKURA.ne.jp>
Date:	Fri, 2 Oct 2015 23:36:47 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	oleg@...hat.com
Cc:	mhocko@...nel.org, akpm@...ux-foundation.org, rientjes@...gle.com,
	kwalker@...hat.com, skozina@...hat.com,
	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()

Oleg Nesterov wrote:
> Tetsuo, sorry, I don't understand your question...
> 
> > because it is possible that T starts the coredump, T sends SIGKILL to P,
> > P calls out_of_memory() on GFP_FS allocation,
> 
> yes, and since fatal_signal_pending() == T we do not even check
> task_will_free_mem().
> 
> > P misses to set SIGKILL on T?
> >
> > Since T sends SIGKILL to all clone(CLONE_VM) tasks upon coredump, P needs
> > to do
> >
> > [...snip...]
> 
> > after mark_oom_victim(current) in case T is not in the same thread group?
> 
> I do not see how this depends on "not in the same thread group". This
> fatal_signal_pending() doesn't look right in any case.

You already answered my question. ;-)
You confirmed this is a possible silent hang up path (I mean, hang up
without OOM killer messages).

> > If yes, what happens if some task failed to receive SIGKILL due to
> > p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN condition?
> 
> Oh. This is another issue. I already tried to suggest to remove this
> check. But this needs more discussion, hopefully we can do this later.

OK.
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