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

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Date:	Thu, 25 Jun 2015 16:11:36 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	fandongdong <fandd@...pur.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

On 2015/6/18 15:54, fandongdong wrote:
> 
> 
> 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
Hi Dongdong,
	I failed to reproduce this issue on my side. Some please help
to confirm?
1) Is this issue reproducible on your side?
2) Does this issue happen if you disable irqbalance service on you
   system?
3) Has the corresponding PCI host bridge been removed before removing
   the socket?

>From the log message, we only noticed log messages for CPU and memory,
but not messages for PCI (IOMMU) devices. And this log message
	"[ 149.976493] acpi ACPI0004:01: Still not present"
implies that the socket has been powered off during the ejection.
So the story may be that you powered off the socket while the host
bridge on the socket is still in use.
Thanks!
Gerry

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