From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756010AbdCTVaU (ORCPT ); Mon, 20 Mar 2017 17:30:20 -0400 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:64369 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755220AbdCTVaQ (ORCPT ); Mon, 20 Mar 2017 17:30:16 -0400 From: "Rafael J. Wysocki" To: Michal Hocko Cc: Toshi Kani , Jiri Kosina , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org Subject: Re: memory hotplug and force_remove Date: Mon, 20 Mar 2017 22:24:42 +0100 Message-ID: <2735706.OR0SQDpVy6@aspire.rjw.lan> User-Agent: KMail/4.14.10 (Linux/4.10.0+; KDE/4.14.9; x86_64; ; ) In-Reply-To: <20170320192938.GA11363@dhcp22.suse.cz> References: <20170320192938.GA11363@dhcp22.suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit 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 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. Thanks, Rafael From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: memory hotplug and force_remove Date: Mon, 20 Mar 2017 22:24:42 +0100 Message-ID: <2735706.OR0SQDpVy6@aspire.rjw.lan> References: <20170320192938.GA11363@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20170320192938.GA11363@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org To: Michal Hocko Cc: Toshi Kani , Jiri Kosina , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org 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. Thanks, Rafael -- 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