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

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Date:	Tue, 31 May 2016 23:48:23 +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>
Subject: Re: [PATCH 5/6] mm, oom: kill all tasks sharing the mm

On 05/31, Michal Hocko wrote:
>
> On Mon 30-05-16 20:18:16, Oleg Nesterov wrote:
> >
> > 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.

Good,

> > 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.

We can't avoid this anyway. use_mm(victim->mm) can be called after we decide to kill
the victim.

So I think that we should always ignore kthreads, and in task_will_free_mem() too.

But let me repeat, I agree we should discuss this later, I am not trying to suggest
this change right now.

Oleg.