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

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Message-ID: <20160530181816.GA25480@redhat.com>
Date:	Mon, 30 May 2016 20:18:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
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>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 5/6] mm, oom: kill all tasks sharing the mm

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.

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.

Oleg.