linux-kernel - Re: [PATCH 0/10 -v4] Handle oom bypass more gracefully

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Message-ID: <20160613141324.GK6518@dhcp22.suse.cz>
Date:	Mon, 13 Jun 2016 16:13:24 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	linux-mm@...ck.org
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/10 -v4] Handle oom bypass more gracefully

On Mon 13-06-16 13:23:48, Michal Hocko wrote:
> On Thu 09-06-16 13:52:07, Michal Hocko wrote:
> > I would like to explore ways how to remove kthreads (use_mm) special
> > case. It shouldn't be that hard, we just have to teach the page fault
> > handler to recognize oom victim mm and enforce EFAULT for kthreads
> > which have borrowed that mm.
> 
> So I was trying to come up with solution for this which would require to
> hook into the pagefault an enforce EFAULT when the mm is being reaped
> by the oom_repaer. Not hard but then I have checked the current users
> and none of them is really needing to read from the userspace (aka
> copy_from_user/get_user). So we actually do not need to do anything
> special.

As pointed out by Tetsuo [1] vhost does realy on copy_from_user. I just
missed that. So scratch this. I will revisit a potential solution for
this but that would be outside of this series scope.

[1] http://lkml.kernel.org/r/201606132252.IAE00593.OJQSFMtVFOLHOF@I-love.SAKURA.ne.jp
-- 
Michal Hocko
SUSE Labs