From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754696AbdC1H6M (ORCPT ); Tue, 28 Mar 2017 03:58:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:57905 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754568AbdC1H6L (ORCPT ); Tue, 28 Mar 2017 03:58:11 -0400 Date: Tue, 28 Mar 2017 09:58:08 +0200 From: Michal Hocko To: "Rafael J. Wysocki" Cc: Toshi Kani , Jiri Kosina , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org Subject: Re: memory hotplug and force_remove Message-ID: <20170328075808.GB18241@dhcp22.suse.cz> References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2735706.OR0SQDpVy6@aspire.rjw.lan> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 20-03-17 22:24:42, Rafael J. Wysocki wrote: > On Monday, March 20, 2017 03:29:39 PM Michal Hocko wrote: > > Hi Rafael, > > Hi, > > > we have been chasing the following BUG() triggering during the memory > > hotremove (remove_memory): > > ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > > check_memblock_offlined_cb); > > if (ret) > > BUG(); > > > > and it took a while to learn that the issue is caused by > > /sys/firmware/acpi/hotplug/force_remove being enabled. I was really > > surprised to see such an option because at least for the memory hotplug > > it cannot work at all. Memory hotplug fails when the memory is still > > in use. Even if we do not BUG() here enforcing the hotplug operation > > will lead to problematic behavior later like crash or a silent memory > > corruption if the memory gets onlined back and reused by somebody else. > > > > I am wondering what was the motivation for introducing this behavior and > > whether there is a way to disallow it for memory hotplug. Or maybe drop > > it completely. What would break in such a case? > > Honestly, I don't remember from the top of my head and I haven't looked at > that code for several months. > > I need some time to recall that. Did you have any chance to look into this? -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: memory hotplug and force_remove Date: Tue, 28 Mar 2017 09:58:08 +0200 Message-ID: <20170328075808.GB18241@dhcp22.suse.cz> References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <2735706.OR0SQDpVy6@aspire.rjw.lan> Sender: owner-linux-mm@kvack.org To: "Rafael J. Wysocki" Cc: Toshi Kani , Jiri Kosina , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On Mon 20-03-17 22:24:42, Rafael J. Wysocki wrote: > On Monday, March 20, 2017 03:29:39 PM Michal Hocko wrote: > > Hi Rafael, > > Hi, > > > we have been chasing the following BUG() triggering during the memory > > hotremove (remove_memory): > > ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > > check_memblock_offlined_cb); > > if (ret) > > BUG(); > > > > and it took a while to learn that the issue is caused by > > /sys/firmware/acpi/hotplug/force_remove being enabled. I was really > > surprised to see such an option because at least for the memory hotplug > > it cannot work at all. Memory hotplug fails when the memory is still > > in use. Even if we do not BUG() here enforcing the hotplug operation > > will lead to problematic behavior later like crash or a silent memory > > corruption if the memory gets onlined back and reused by somebody else. > > > > I am wondering what was the motivation for introducing this behavior and > > whether there is a way to disallow it for memory hotplug. Or maybe drop > > it completely. What would break in such a case? > > Honestly, I don't remember from the top of my head and I haven't looked at > that code for several months. > > I need some time to recall that. Did you have any chance to look into this? -- 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