From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933267AbdCUQO0 (ORCPT ); Tue, 21 Mar 2017 12:14:26 -0400 Received: from smtp.nue.novell.com ([195.135.221.5]:43562 "EHLO smtp.nue.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933138AbdCUQOY (ORCPT ); Tue, 21 Mar 2017 12:14:24 -0400 Date: Wed, 22 Mar 2017 00:13:56 +0800 From: joeyli To: "Rafael J. Wysocki" Cc: Michal Hocko , Toshi Kani , Jiri Kosina , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org Subject: Re: memory hotplug and force_remove Message-ID: <20170321161356.GA20835@linux-l9pv.suse> 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/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 20, 2017 at 10:24:42PM +0100, 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. > IMHO. In the second pass offline in acpi_scan_try_to_offline(), when force_remove flag enabled, it's still run offline on the parent device even there have any child device offline failed. And it doesn't return the error from acpi_bus_offline() to caller. errdev = NULL; acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX, NULL, acpi_bus_offline, (void *)true, (void **)&errdev); if (!errdev || acpi_force_hot_remove) acpi_bus_offline(handle, 0, (void *)true, (void **)&errdev); In this situation, the parent device or any child device may not really offline successfully. But acpi_scan_hot_remove, the caller doesn't know that. Then it cause the later acpi_bus_trim() process failed. acpi_bus_trim() -> handler->detach() -> acpi_memory_device_remove() -> remove_memory() -> BUG() because some memory doesn't really offline. Thanks a lot! Joey Lee From mboxrd@z Thu Jan 1 00:00:00 1970 From: joeyli Subject: Re: memory hotplug and force_remove Date: Wed, 22 Mar 2017 00:13:56 +0800 Message-ID: <20170321161356.GA20835@linux-l9pv.suse> 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: Michal Hocko , Toshi Kani , Jiri Kosina , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org On Mon, Mar 20, 2017 at 10:24:42PM +0100, 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. > IMHO. In the second pass offline in acpi_scan_try_to_offline(), when force_remove flag enabled, it's still run offline on the parent device even there have any child device offline failed. And it doesn't return the error from acpi_bus_offline() to caller. errdev = NULL; acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX, NULL, acpi_bus_offline, (void *)true, (void **)&errdev); if (!errdev || acpi_force_hot_remove) acpi_bus_offline(handle, 0, (void *)true, (void **)&errdev); In this situation, the parent device or any child device may not really offline successfully. But acpi_scan_hot_remove, the caller doesn't know that. Then it cause the later acpi_bus_trim() process failed. acpi_bus_trim() -> handler->detach() -> acpi_memory_device_remove() -> remove_memory() -> BUG() because some memory doesn't really offline. Thanks a lot! Joey Lee -- 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