From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932097AbcFNURs (ORCPT ); Tue, 14 Jun 2016 16:17:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47826 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751765AbcFNURq (ORCPT ); Tue, 14 Jun 2016 16:17:46 -0400 Date: Tue, 14 Jun 2016 22:17:40 +0200 From: Oleg Nesterov To: Michal Hocko Cc: linux-mm@kvack.org, Tetsuo Handa , David Rientjes , Vladimir Davydov , Andrew Morton , LKML Subject: Re: [PATCH 0/10 -v4] Handle oom bypass more gracefully Message-ID: <20160614201740.GA617@redhat.com> References: <1465473137-22531-1-git-send-email-mhocko@kernel.org> <20160613112348.GC6518@dhcp22.suse.cz> <20160613141324.GK6518@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160613141324.GK6518@dhcp22.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Tue, 14 Jun 2016 20:17:46 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/13, Michal Hocko wrote: > > 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. Tetsuo, Michal, but do we really care? I have no idea what vhost does, but obviously this should not lead to kernel crash or something like this, otherwise it should be fixed. If we are going to kill the owner of dev->mm anyway, why should we worry about vhost_worker() which can fail to access this ->mm after that? So to me this additional patch looks fine, but probably I missed something? Oleg.