From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 8C8896B0033 for ; Wed, 8 Feb 2017 10:21:10 -0500 (EST) Received: by mail-wm0-f71.google.com with SMTP id v77so31230231wmv.5 for ; Wed, 08 Feb 2017 07:21:10 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id m87si2806065wmc.35.2017.02.08.07.21.09 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 08 Feb 2017 07:21:09 -0800 (PST) Date: Wed, 8 Feb 2017 16:21:07 +0100 From: Michal Hocko Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc Message-ID: <20170208152106.GP5686@dhcp22.suse.cz> References: <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> <20170208073527.GA5686@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: Christoph Lameter Cc: Thomas Gleixner , Mel Gorman , Vlastimil Babka , Dmitry Vyukov , Tejun Heo , "linux-mm@kvack.org" , LKML , Ingo Molnar , Peter Zijlstra , syzkaller , Andrew Morton On Wed 08-02-17 09:11:06, Cristopher Lameter wrote: > On Wed, 8 Feb 2017, Michal Hocko wrote: > > > > 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] > > That is nonsense. stop_machine would be used when adding removing a > processor. There would be no need to synchronize when looping over active > cpus anymore. get_online_cpus() etc would be removed from the hot > path since the cpu masks are guaranteed to be stable. I have no idea what you are trying to say and how this is related to the deadlock we are discussing here. We certainly do not need to add stop_machine the problem. And yeah, dropping get_online_cpus was possible after considering all fallouts. -- 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