linux-kernel - Re: Panic when cpu hot-remove

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Date:	Thu, 18 Jun 2015 15:54:15 +0800
From:	fandongdong <fandd@...pur.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Joerg Roedeljoro <joro@...tes.org>
CC:	刘长生 <liuchangsheng@...pur.com>,
	iommu <iommu@...ts.linux-foundation.org>,
	"jiang.liu@...el.com" <jiang.liu@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	闫晓峰 <yanxiaofeng@...pur.com>,
	Roland Dreier <roland@...nel.org>
Subject: Re: Panic when cpu hot-remove



在 2015/6/18 15:27, fandongdong 写道:
>
>
> 在 2015/6/18 13:40, Jiang Liu 写道:
>> On 2015/6/17 22:36, Alex Williamson wrote:
>>> On Wed, 2015-06-17 at 13:52 +0200, Joerg Roedeljoro wrote:
>>>> On Wed, Jun 17, 2015 at 10:42:49AM +0000, 范冬冬 wrote:
>>>>> Hi maintainer,
>>>>>
>>>>> We found a problem that a panic happen when cpu was hot-removed. 
>>>>> We also trace the problem according to the calltrace information.
>>>>> An endless loop happen because value head is not equal to value 
>>>>> tail forever in the function qi_check_fault( ).
>>>>> The location code is as follows:
>>>>>
>>>>>
>>>>> do {
>>>>>          if (qi->desc_status[head] == QI_IN_USE)
>>>>>          qi->desc_status[head] = QI_ABORT;
>>>>>          head = (head - 2 + QI_LENGTH) % QI_LENGTH;
>>>>>      } while (head != tail);
>>>> Hmm, this code interates only over every second QI descriptor, and 
>>>> tail
>>>> probably points to a descriptor that is not iterated over.
>>>>
>>>> Jiang, can you please have a look?
>>> I think that part is normal, the way we use the queue is to always
>>> submit a work operation followed by a wait operation so that we can
>>> determine the work operation is complete.  That's done via
>>> qi_submit_sync().  We have had spurious reports of the queue getting
>>> impossibly out of sync though.  I saw one that was somehow linked to 
>>> the
>>> I/O AT DMA engine.  Roland Dreier saw something similar[1]. I'm not
>>> sure if they're related to this, but maybe worth comparing. Thanks,
>> Thanks, Alex and Joerg!
>>
>> Hi Dongdong,
>>     Could you please help to give some instructions about how to
>> reproduce this issue? I will try to reproduce it if possible.
>> Thanks!
>> Gerry
> Hi Gerry,
>
> We're running kernel 4.1.0 on a 4-socket system and  we want to 
> offline socket 1.
> Steps as follows:
>
> echo 1 > /sys/firmware/acpi/hotplug/force_remove
> echo 1 > /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0004:01/eject
>
> Thanks!
> Dongdong
>>> Alex
>>>
>>> [1] 
>>> http://lists.linuxfoundation.org/pipermail/iommu/2015-January/011502.html
>>>
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>> .
>>
>

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