From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754857AbdBGQW3 (ORCPT ); Tue, 7 Feb 2017 11:22:29 -0500 Received: from outbound-smtp08.blacknight.com ([46.22.139.13]:57337 "EHLO outbound-smtp08.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753497AbdBGQW2 (ORCPT ); Tue, 7 Feb 2017 11:22:28 -0500 Date: Tue, 7 Feb 2017 16:22:24 +0000 From: Mel Gorman To: Michal Hocko Cc: Vlastimil Babka , Dmitry Vyukov , Tejun Heo , Christoph Lameter , "linux-mm@kvack.org" , LKML , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , syzkaller , Andrew Morton Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc Message-ID: <20170207162224.elnrlgibjegswsgn@techsingularity.net> References: <20170207094300.cuxfqi35wflk5nr5@techsingularity.net> <2cdef192-1939-d692-1224-8ff7d7ff7203@suse.cz> <20170207102809.awh22urqmfrav5r6@techsingularity.net> <20170207103552.GH5065@dhcp22.suse.cz> <20170207113435.6xthczxt2cx23r4t@techsingularity.net> <20170207114327.GI5065@dhcp22.suse.cz> <20170207123708.GO5065@dhcp22.suse.cz> <20170207135846.usfrn7e4znjhmogn@techsingularity.net> <20170207141911.GR5065@dhcp22.suse.cz> <20170207153459.GV5065@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20170207153459.GV5065@dhcp22.suse.cz> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 07, 2017 at 04:34:59PM +0100, Michal Hocko wrote: > > But we do not care about the whole cpu hotplug code. The only part we > > really do care about is the race inside drain_pages_zone and that will > > run in an atomic context on the specific CPU. > > > > You are absolutely right that using the mutex is safe as well but the > > hotplug path is already littered with locks and adding one more to the > > picture doesn't sound great to me. So I would really like to not use a > > lock if that is possible and safe (with a big fat comment of course). > > And with the full changelog. I hope I haven't missed anything this time. > --- > From 8c6af3116520251cc4ec2213f0a4ed2544bb4365 Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Tue, 7 Feb 2017 16:08:35 +0100 > Subject: [PATCH] mm, page_alloc: do not depend on cpu hotplug locks inside the > allocator > > > > Reported-by: Dmitry Vyukov > Signed-off-by: Michal Hocko Not that I can think of. It's almost identical to the diff I posted with the exception of the mutex in the cpu hotplug teardown path. I agree that in the current implementation that it should be unnecessary even if I thought it would be more robust against any other hotplug churn. Acked-by: Mel Gorman -- Mel Gorman SUSE Labs