From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f197.google.com (mail-wj0-f197.google.com [209.85.210.197]) by kanga.kvack.org (Postfix) with ESMTP id A1A046B0033 for ; Wed, 8 Feb 2017 02:35:31 -0500 (EST) Received: by mail-wj0-f197.google.com with SMTP id an2so31104302wjc.3 for ; Tue, 07 Feb 2017 23:35:31 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id q4si8124747wra.220.2017.02.07.23.35.29 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 07 Feb 2017 23:35:30 -0800 (PST) Date: Wed, 8 Feb 2017 08:35:28 +0100 From: Michal Hocko Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc Message-ID: <20170208073527.GA5686@dhcp22.suse.cz> References: <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> <20170207162224.elnrlgibjegswsgn@techsingularity.net> <20170207164130.GY5065@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Thomas Gleixner Cc: Christoph Lameter , Mel Gorman , Vlastimil Babka , Dmitry Vyukov , Tejun Heo , "linux-mm@kvack.org" , LKML , Ingo Molnar , Peter Zijlstra , syzkaller , Andrew Morton On Tue 07-02-17 23:25:17, Thomas Gleixner wrote: > On Tue, 7 Feb 2017, Christoph Lameter wrote: > > On Tue, 7 Feb 2017, Michal Hocko wrote: > > > > > I am always nervous when seeing hotplug locks being used in low level > > > code. It has bitten us several times already and those deadlocks are > > > quite hard to spot when reviewing the code and very rare to hit so they > > > tend to live for a long time. > > > > Yep. Hotplug events are pretty significant. Using stop_machine_XXXX() etc > > would be advisable and that would avoid the taking of locks and get rid of all the > > ocmplexity, reduce the code size and make the overall system much more > > reliable. > > Huch? stop_machine() is horrible and heavy weight. Don't go there, there > must be simpler solutions than that. Absolutely agreed. We are in the page allocator path so using the stop_machine* is just ridiculous. And, in fact, there is a much simpler solution [1] [1] http://lkml.kernel.org/r/20170207201950.20482-1-mhocko@kernel.org -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org