Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752279AbdGDMtv (ORCPT ); Tue, 4 Jul 2017 08:49:51 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:48099 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752038AbdGDMtu (ORCPT ); Tue, 4 Jul 2017 08:49:50 -0400 Date: Tue, 4 Jul 2017 14:49:47 +0200 (CEST) From: Thomas Gleixner To: Vlastimil Babka cc: LKML , linux-mm@kvack.org, Andrey Ryabinin , Michal Hocko , Andrew Morton , Vladimir Davydov , Peter Zijlstra Subject: Re: [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem In-Reply-To: Message-ID: References: <20170704093232.995040438@linutronix.de> <20170704093421.506836322@linutronix.de> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1192 Lines: 32 On Tue, 4 Jul 2017, Vlastimil Babka wrote: > On 07/04/2017 11:32 AM, Thomas Gleixner wrote: > > Andrey reported a potential deadlock with the memory hotplug lock and the > > cpu hotplug lock. > > > > The reason is that memory hotplug takes the memory hotplug lock and then > > calls stop_machine() which calls get_online_cpus(). That's the reverse lock > > order to get_online_cpus(); get_online_mems(); in mm/slub_common.c > > > > The problem has been there forever. The reason why this was never reported > > is that the cpu hotplug locking had this homebrewn recursive reader writer > > semaphore construct which due to the recursion evaded the full lock dep > > coverage. The memory hotplug code copied that construct verbatim and > > therefor has similar issues. > > > > Three steps to fix this: > > > > 1) Convert the memory hotplug locking to a per cpu rwsem so the potential > > issues get reported proper by lockdep. > > > > 2) Lock the online cpus in mem_hotplug_begin() before taking the memory > > hotplug rwsem and use stop_machine_cpuslocked() in the page_alloc code > > and use to avoid recursive locking. > > ^ s/and use // ? Ooops, yes. Thanks, tglx