From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932961AbdCaMCl (ORCPT ); Fri, 31 Mar 2017 08:02:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:34793 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751297AbdCaMCk (ORCPT ); Fri, 31 Mar 2017 08:02:40 -0400 Date: Fri, 31 Mar 2017 14:02:36 +0200 From: Michal Hocko To: joeyli Cc: "Rafael J. Wysocki" , Kani Toshimitsu , Jiri Kosina , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org Subject: Re: memory hotplug and force_remove Message-ID: <20170331120236.GO27098@dhcp22.suse.cz> References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> <20170328075808.GB18241@dhcp22.suse.cz> <2203902.lsAnRkUs2Y@aspire.rjw.lan> <20170331083017.GK27098@dhcp22.suse.cz> <20170331104905.GA28365@linux-l9pv.suse> <20170331105505.GM27098@dhcp22.suse.cz> <20170331115530.GB28365@linux-l9pv.suse> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170331115530.GB28365@linux-l9pv.suse> 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 Fri 31-03-17 19:55:30, Joey Lee wrote: > On Fri, Mar 31, 2017 at 12:55:05PM +0200, Michal Hocko wrote: > > On Fri 31-03-17 18:49:05, Joey Lee wrote: > > > Hi Michal, > > > > > > On Fri, Mar 31, 2017 at 10:30:17AM +0200, Michal Hocko wrote: > > [...] > > > > @@ -241,11 +232,10 @@ static int acpi_scan_try_to_offline(struct acpi_device *device) > > > > acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX, > > > > NULL, acpi_bus_offline, (void *)true, > > > > (void **)&errdev); > > > > - if (!errdev || acpi_force_hot_remove) > > > > + if (!errdev) > > > > acpi_bus_offline(handle, 0, (void *)true, > > > > (void **)&errdev); > > > > - > > > > - if (errdev && !acpi_force_hot_remove) { > > > > + else { > > > ^^^^^^^^^^^^^ > > > Here should still checks the parent's errdev state then rollback > > > parent/children to online state: > > > > > > - if (errdev && !acpi_force_hot_remove) { > > > + if (errdev) { > > > > You are right, I have missed that acpi_bus_offline modifies errdev. > > Thanks for spotting that! Updated patch is below. > > --- > > >From 8df0abd29988ffb52b6df52407b96d6015861bb7 Mon Sep 17 00:00:00 2001 > > From: Michal Hocko > > Date: Fri, 31 Mar 2017 10:08:41 +0200 > > Subject: [PATCH] acpi: drop support for force_remove > > > > /sys/firmware/acpi/hotplug/force_remove was presumably added to support > > auto offlining in the past. This is, however, inherently dangerous for > > some hotplugable resources like memory. The memory offlining fails when > > the memory is still in use and cannot be dropped or migrated. If we > > ignore the failure we are basically allowing for subtle memory > > corruption or a crash. > > > > We have actually noticed the later while hitting BUG() 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(); > > > > it took us quite non-trivial time realize that the customer had > > force_remove enabled. Even if the BUG was removed here and we could > > propagate the error up the call chain it wouldn't help at all because > > then we would hit a crash or a memory corruption later and harder to > > debug. So force_remove is unfixable for the memory hotremove. We haven't > > checked other hotplugable resources to be prone to a similar problems. > > > > Remove the force_remove functionality because it is not fixable currently. > > Keep the sysfs file and report an error if somebody tries to enable it. > > Encourage users to report about the missing functionality and work with > > them with an alternative solution. > > > > Signed-off-by: Michal Hocko > > This patch is good to me. Please feel free to add: > > Reviewed-by: Lee, Chun-Yi Thanks for the review Joey! -- 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: Fri, 31 Mar 2017 14:02:36 +0200 Message-ID: <20170331120236.GO27098@dhcp22.suse.cz> References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> <20170328075808.GB18241@dhcp22.suse.cz> <2203902.lsAnRkUs2Y@aspire.rjw.lan> <20170331083017.GK27098@dhcp22.suse.cz> <20170331104905.GA28365@linux-l9pv.suse> <20170331105505.GM27098@dhcp22.suse.cz> <20170331115530.GB28365@linux-l9pv.suse> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20170331115530.GB28365@linux-l9pv.suse> Sender: owner-linux-mm@kvack.org To: joeyli Cc: "Rafael J. Wysocki" , Kani Toshimitsu , Jiri Kosina , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On Fri 31-03-17 19:55:30, Joey Lee wrote: > On Fri, Mar 31, 2017 at 12:55:05PM +0200, Michal Hocko wrote: > > On Fri 31-03-17 18:49:05, Joey Lee wrote: > > > Hi Michal, > > > > > > On Fri, Mar 31, 2017 at 10:30:17AM +0200, Michal Hocko wrote: > > [...] > > > > @@ -241,11 +232,10 @@ static int acpi_scan_try_to_offline(struct acpi_device *device) > > > > acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX, > > > > NULL, acpi_bus_offline, (void *)true, > > > > (void **)&errdev); > > > > - if (!errdev || acpi_force_hot_remove) > > > > + if (!errdev) > > > > acpi_bus_offline(handle, 0, (void *)true, > > > > (void **)&errdev); > > > > - > > > > - if (errdev && !acpi_force_hot_remove) { > > > > + else { > > > ^^^^^^^^^^^^^ > > > Here should still checks the parent's errdev state then rollback > > > parent/children to online state: > > > > > > - if (errdev && !acpi_force_hot_remove) { > > > + if (errdev) { > > > > You are right, I have missed that acpi_bus_offline modifies errdev. > > Thanks for spotting that! Updated patch is below. > > --- > > >From 8df0abd29988ffb52b6df52407b96d6015861bb7 Mon Sep 17 00:00:00 2001 > > From: Michal Hocko > > Date: Fri, 31 Mar 2017 10:08:41 +0200 > > Subject: [PATCH] acpi: drop support for force_remove > > > > /sys/firmware/acpi/hotplug/force_remove was presumably added to support > > auto offlining in the past. This is, however, inherently dangerous for > > some hotplugable resources like memory. The memory offlining fails when > > the memory is still in use and cannot be dropped or migrated. If we > > ignore the failure we are basically allowing for subtle memory > > corruption or a crash. > > > > We have actually noticed the later while hitting BUG() 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(); > > > > it took us quite non-trivial time realize that the customer had > > force_remove enabled. Even if the BUG was removed here and we could > > propagate the error up the call chain it wouldn't help at all because > > then we would hit a crash or a memory corruption later and harder to > > debug. So force_remove is unfixable for the memory hotremove. We haven't > > checked other hotplugable resources to be prone to a similar problems. > > > > Remove the force_remove functionality because it is not fixable currently. > > Keep the sysfs file and report an error if somebody tries to enable it. > > Encourage users to report about the missing functionality and work with > > them with an alternative solution. > > > > Signed-off-by: Michal Hocko > > This patch is good to me. Please feel free to add: > > Reviewed-by: Lee, Chun-Yi Thanks for the review Joey! -- 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