linux-kernel - Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes sharing mm

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Message-ID: <20181009132622.GR8528@dhcp22.suse.cz>
Date:   Tue, 9 Oct 2018 15:26:22 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     ytk.lee@...sung.com, "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes
 sharing mm

On Tue 09-10-18 22:14:24, Tetsuo Handa wrote:
> On 2018/10/09 21:58, Michal Hocko wrote:
> > On Tue 09-10-18 21:52:12, Tetsuo Handa wrote:
> >> On 2018/10/09 20:10, Michal Hocko wrote:
> >>> On Tue 09-10-18 19:00:44, Tetsuo Handa wrote:
> >>>>> 2) add OOM_SCORE_ADJ_MIN and do not kill tasks sharing mm and do not
> >>>>> reap the mm in the rare case of the race.
> >>>>
> >>>> That is no problem. The mistake we made in 4.6 was that we updated oom_score_adj
> >>>> to -1000 (and allowed unprivileged users to OOM-lockup the system).
> >>>
> >>> I do not follow.
> >>>
> >>
> >> http://tomoyo.osdn.jp/cgi-bin/lxr/source/mm/oom_kill.c?v=linux-4.6.7#L493
> > 
> > Ahh, so you are not referring to the current upstream code. Do you see
> > any specific problem with the current one (well, except for the possible
> > race which I have tried to evaluate).
> > 
> 
> Yes. "task_will_free_mem(current) in out_of_memory() returns false due to MMF_OOM_SKIP
> being already set" is a problem for clone(CLONE_VM without CLONE_THREAD/CLONE_SIGHAND)
> with the current code.

a) I fail to see how that is related to your previous post and b) could
you be more specific. Is there any other scenario from the two described
in my earlier email?
-- 
Michal Hocko
SUSE Labs