From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yasuaki Ishimatsu Subject: Re: acpi_bus_trim does not detach devices in post order Date: Wed, 7 Aug 2013 12:21:10 +0900 Message-ID: <5201BD26.8000404@jp.fujitsu.com> References: <52006888.5030203@jp.fujitsu.com> <8453998.khIH1RyxM0@vostro.rjw.lan> <52019667.3010405@jp.fujitsu.com> <11026265.tBv8b0WrJO@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:35059 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756894Ab3HGDVr (ORCPT ); Tue, 6 Aug 2013 23:21:47 -0400 In-Reply-To: <11026265.tBv8b0WrJO@vostro.rjw.lan> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Rafael J. Wysocki" Cc: rafael.j.wysocki@intel.com, yinghai@kernel.org, toshi.kani@hp.com, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org (2013/08/07 9:57), Rafael J. Wysocki wrote: > On Wednesday, August 07, 2013 09:35:51 AM Yasuaki Ishimatsu wrote: >> (2013/08/06 23:26), Rafael J. Wysocki wrote: >>> On Tuesday, August 06, 2013 07:06:37 PM Yasuaki Ishimatsu wrote: >>>> (2013/08/06 12:07), Yasuaki Ishimatsu wrote: >>>>> >>>>> I acked the following commit but I hit a problem by the commit. >>>>> So I report it. >>>>> >>>>> commit cecdb193c8d91a42d9489d00618cc3dfff92e55a >>>>> Author: Rafael J. Wysocki >>>>> Date: Tue Jan 15 13:24:02 2013 +0100 >>>>> >>>>> ACPI / scan: Change the implementation of acpi_bus_trim() >>>>> >>>>> Before applying the commit, acpi_bus_trim() detachs devices in post order. >>>>> >>>>> When I hot add memory devices and processor devices by container device >>>>> in my x86 box, memory devices are added first and processor devices are added >>>>> second. So I expect that processor devices are removed first and memory >>>>> devices are removed second when I remove them. And before applying the >>>>> commit, acpi_bus_trim() did so. >>>>> >>>>> But after appling the commit, acpi_bus_trim() does not detach devices in >>>>> post order. So when I remove them, memory devices are removed first and >>>>> processor devices are removed second. >>>>> >>>>> By this, I hit a problem. >>>>> >>>>> In Linux on x86 arch, NUMA node is depend on memory devices. So new NUMA >>>>> node is created at memory hot adding. Thus when I hot add memory devices and >>>>> processor devices, we must hot add memory device first. Otherwise, processor >>>>> devices are not set to correct NUMA node number. >>>>> >>>>> And Linux expects that when removing them, processor devices are removed >>>>> first before removing memory devices. But acpi_bus_trim() does not do so. >>>>> By this, NUMA node is not cleared in my x86 box when hot removing memory device >>>>> and processor devices. When removing memory devices, NUMA node is cleared. >>>>> But if there are processor devices related with the NUMA node, NUMA node is >>>>> not be cleared at memory hot removing. >>>>> >>>>> So when I remove them, NUMA node's sysfs file remained as follows: >>>> >>>> I had little mistake. CPU also tries to clear NUMA node. >>>> But current implementation has bug. So I'll fix it. >>> >> >>> Do I understand correctly that with your fix at >>> >>> https://patchwork.kernel.org/patch/2839298/ >>> >>> the current acpi_bus_trim() implementation will be sufficient? >> >> No. The patch just fixed implementation of CPU hotplug. > > My question was not sufficiently precise. :-) > > I wanted to ask if your patch was sufficient to address the specific breakage > you were seeing without modifying acpi_bus_trim(). Ah. Yes. By my patch, node sysfs is deleted correctly. > >> A problem I think is that acpi_bus_trim() does not detach devices in >> post-order. > > That is not exactly post-order, but children are guaranteed to be processed > before their parents. If that guarantee is sufficient, there's no problem. > Otherwise, acpi_bus_trim() may need to be modified, but first I'd like to > see a real life example where that really matters. Currently I have no idea. Thanks, Yasuaki Ishimatsu >> And my patch does not fix it. So if some device has dependency >> of other device, similar problem will occur. > > If there is a dependency that is not a parent-child one, we'll have a problem, > but in that case relying on ordering will not be robust enough anyway in my > opinion. > > Thanks, > Rafael > >