From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id DB71F6B0069 for ; Tue, 7 Feb 2017 08:58:49 -0500 (EST) Received: by mail-wm0-f72.google.com with SMTP id x4so25552851wme.3 for ; Tue, 07 Feb 2017 05:58:49 -0800 (PST) Received: from outbound-smtp07.blacknight.com (outbound-smtp07.blacknight.com. [46.22.139.12]) by mx.google.com with ESMTPS id u203si12263162wmu.140.2017.02.07.05.58.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 07 Feb 2017 05:58:47 -0800 (PST) Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp07.blacknight.com (Postfix) with ESMTPS id 60F461C1731 for ; Tue, 7 Feb 2017 13:58:47 +0000 (GMT) Date: Tue, 7 Feb 2017 13:58:46 +0000 From: Mel Gorman Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc Message-ID: <20170207135846.usfrn7e4znjhmogn@techsingularity.net> References: <20170206220530.apvuknbagaf2rdlw@techsingularity.net> <20170207084855.GC5065@dhcp22.suse.cz> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20170207123708.GO5065@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: 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 On Tue, Feb 07, 2017 at 01:37:08PM +0100, Michal Hocko wrote: > > You cannot put sleepable lock inside the preempt disbaled section... > > We can make it a spinlock right? > > Scratch that! For some reason I thought that cpu notifiers are run in an > atomic context. Now that I am checking the code again it turns out I was > wrong. __cpu_notify uses __raw_notifier_call_chain so this is not an > atomic context. Indeed. > Anyway, shouldn't be it sufficient to disable preemption > on drain_local_pages_wq? That would be sufficient for a hot-removed CPU moving the drain request to another CPU and avoiding any scheduling events. > The CPU hotplug callback will not preempt us > and so we cannot work on the same cpus, right? > I don't see a specific guarantee that it cannot be preempted and it would depend on an the exact cpu hotplug implementation which is subject to quite a lot of change. Hence, the mutex provides a guantee that the hot-removed CPU teardown cannot run on the same CPU as a workqueue drain running on a CPU it was not originally scheduled for. -- Mel Gorman 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