linux-kernel - Re: acpi_bus_trim does not detach devices in post order

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Message-ID: <52019667.3010405@jp.fujitsu.com>
Date:	Wed, 7 Aug 2013 09:35:51 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	<rafael.j.wysocki@...el.com>, <yinghai@...nel.org>,
	<toshi.kani@...com>, <linux-acpi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: acpi_bus_trim does not detach devices in post order

(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@...el.com>
>>> 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.

A problem I think is that acpi_bus_trim() does not detach devices in
post-order. And my patch does not fix it. So if some device has dependency
of other device, similar problem will occur.

Thanks,
Yasuaki Ishimatsu

>
> Rafael
>
>


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