From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754017AbdC3Is6 (ORCPT ); Thu, 30 Mar 2017 04:48:58 -0400 Received: from mx2.suse.de ([195.135.220.15]:33133 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752739AbdC3Irz (ORCPT ); Thu, 30 Mar 2017 04:47:55 -0400 Date: Thu, 30 Mar 2017 10:47:52 +0200 (CEST) From: Jiri Kosina X-X-Sender: jkosina@pobox.suse.cz To: "Rafael J. Wysocki" cc: Michal Hocko , Toshi Kani , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org Subject: Re: memory hotplug and force_remove In-Reply-To: <2203902.lsAnRkUs2Y@aspire.rjw.lan> Message-ID: References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> <20170328075808.GB18241@dhcp22.suse.cz> <2203902.lsAnRkUs2Y@aspire.rjw.lan> User-Agent: Alpine 2.20 (LSU 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 On Tue, 28 Mar 2017, Rafael J. Wysocki wrote: > > > > 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? > > Well, yes. > > It looks like that was added for some people who depended on the old behavior > at that time. > > I guess we can try to drop it and see what happpens. :-) I'd agree with that; at the same time, udev rule should be submitted to systemd folks though. I don't think there is anything existing in this area yet (neither do distros ship their own udev rules for this AFAIK). Thanks, -- Jiri Kosina SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Kosina Subject: Re: memory hotplug and force_remove Date: Thu, 30 Mar 2017 10:47:52 +0200 (CEST) Message-ID: References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> <20170328075808.GB18241@dhcp22.suse.cz> <2203902.lsAnRkUs2Y@aspire.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <2203902.lsAnRkUs2Y@aspire.rjw.lan> Sender: owner-linux-mm@kvack.org To: "Rafael J. Wysocki" Cc: Michal Hocko , Toshi Kani , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On Tue, 28 Mar 2017, Rafael J. Wysocki wrote: > > > > 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? > > Well, yes. > > It looks like that was added for some people who depended on the old behavior > at that time. > > I guess we can try to drop it and see what happpens. :-) I'd agree with that; at the same time, udev rule should be submitted to systemd folks though. I don't think there is anything existing in this area yet (neither do distros ship their own udev rules for this AFAIK). Thanks, -- Jiri Kosina 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