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 <rafael.j.wysocki@xxxxxxxxx> > >>> 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(). > 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. > 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 -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
