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Date: Mon, 13 Jun 2016 13:23:49 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 0/10 -v4] Handle oom bypass more gracefully
Message-ID: <20160613112348.GC6518@dhcp22.suse.cz>
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Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, David Rientjes <rientjes@google.com>, Oleg Nesterov <oleg@redhat.com>, Vladimir Davydov <vdavydov@parallels.com>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>

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. Copying _to_ the userspace should be OK because there is no
risk of the corruption. So I believe we should be able to simply do the
following. Or is anybody seeing a reason this would be unsafe?
---