From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753817AbcFPGd5 (ORCPT ); Thu, 16 Jun 2016 02:33:57 -0400 Received: from mail-pf0-f170.google.com ([209.85.192.170]:35067 "EHLO mail-pf0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753801AbcFPGdw (ORCPT ); Thu, 16 Jun 2016 02:33:52 -0400 Date: Thu, 16 Jun 2016 08:33:48 +0200 From: Michal Hocko To: Oleg Nesterov 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: <20160616063347.GD30768@dhcp22.suse.cz> References: <1465473137-22531-1-git-send-email-mhocko@kernel.org> <20160613112348.GC6518@dhcp22.suse.cz> <20160613141324.GK6518@dhcp22.suse.cz> <20160614201740.GA617@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160614201740.GA617@redhat.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 14-06-16 22:17:40, Oleg Nesterov wrote: > 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? This needs a deeper investigation. It relies on some state flags copied from the userspace. I suspect it might misbehave but let's leave this alone for a while. It is more complicated than I expected. -- Michal Hocko SUSE Labs