linux-kernel - Re: [PATCH 5/6] mm, oom: kill all tasks sharing the mm

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Date:	Tue, 31 May 2016 09:43:18 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-mm@...ck.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] mm, oom: kill all tasks sharing the mm

On Mon 30-05-16 20:18:16, Oleg Nesterov wrote:
> On 05/30, Michal Hocko wrote:
> >
> > @@ -852,8 +852,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
> >  			continue;
> >  		if (same_thread_group(p, victim))
> >  			continue;
> > -		if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p) ||
> > -		    p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
> > +		if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p)) {
> >  			/*
> >  			 * We cannot use oom_reaper for the mm shared by this
> >  			 * process because it wouldn't get killed and so the
> > @@ -862,6 +861,11 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
> >  			can_oom_reap = false;
> >  			continue;
> >  		}
> > +		if (p->signal->oom_score_adj == OOM_ADJUST_MIN)
> > +			pr_warn("%s pid=%d shares mm with oom disabled %s pid=%d. Seems like misconfiguration, killing anyway!"
> > +					" Report at linux-mm@...ck.org\n",
> > +					victim->comm, task_pid_nr(victim),
> > +					p->comm, task_pid_nr(p));
> 
> Oh, yes, I personally do agree ;)
> 
> perhaps the is_global_init() == T case needs a warning too? the previous changes
> take care about vfork() from /sbin/init, so the only reason we can see it true
> is that /sbin/init shares the memory with a memory hog... Nevermind, forget.

I have another two patches waiting for this to settle and one of them
adds a warning to that path.

> This is a bit off-topic, but perhaps we can also change the PF_KTHREAD check later.
> Of course we should not try to kill this kthread, but can_oom_reap can be true in
> this case. A kernel thread which does use_mm() should handle the errors correctly
> if (say) get_user() fails because we unmap the memory.

I was worried that the kernel thread would see a zero page so this could
lead to a data corruption.
-- 
Michal Hocko
SUSE Labs