From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754213AbcDMTsO (ORCPT ); Wed, 13 Apr 2016 15:48:14 -0400 Received: from mail-yw0-f194.google.com ([209.85.161.194]:36574 "EHLO mail-yw0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753827AbcDMThh (ORCPT ); Wed, 13 Apr 2016 15:37:37 -0400 Date: Wed, 13 Apr 2016 15:37:34 -0400 From: Tejun Heo To: Michal Hocko Cc: Petr Mladek , cgroups@vger.kernel.org, Cyril Hrubis , linux-kernel@vger.kernel.org, Johannes Weiner Subject: Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Message-ID: <20160413193734.GC20142@htj.duckdns.org> References: <20160413094216.GC5774@pathway.suse.cz> <20160413183309.GG3676@htj.duckdns.org> <20160413192313.GA30260@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160413192313.GA30260@dhcp22.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Michal. On Wed, Apr 13, 2016 at 09:23:14PM +0200, Michal Hocko wrote: > I think we can live without lru_add_drain_all() in the migration path. > We are talking about 4 pagevecs so 56 pages. The charge migration is Ah, nice. > racy anyway. What concerns me more is how all this is fragile. It sounds > just too easy to add a dependency on per-cpu sync work later and > reintroduce this issue which is quite hard to detect. > Cannot we come up with something more robust? Or at least warn when we > try to use per-cpu workers with problematic locks held? Yeah, workqueue does limited lockdep annotation but it doesn't integrate fully with the rest of dependency tracking. It'd be nice to have that. Don't know how to tho. Thanks. -- tejun