Re: Panic when cpu hot-remove

From: fandongdong <fandd-6gUaA8visnnQT0dZR+AlfA@public.gmane.org>
To: Jiang Liu <jiang.liu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>,
	Alex Williamson
	<alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Joerg Roedeljoro <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>
Cc: "Roland Dreier" <roland-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	闫晓峰 <yanxiaofeng-6gUaA8visnnQT0dZR+AlfA@public.gmane.org>,
	"jiang.liu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org"
	<jiang.liu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	linux-kernel
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	刘长生 <liuchangsheng-6gUaA8visnnQT0dZR+AlfA@public.gmane.org>,
	iommu
	<iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>
Subject: Re: Panic when cpu hot-remove
Date: Thu, 18 Jun 2015 15:54:15 +0800	[thread overview]
Message-ID: <55827927.4080504@inspur.com> (raw)
In-Reply-To: <558272E3.4000504-6gUaA8visnnQT0dZR+AlfA@public.gmane.org>


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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