Re: Panic when cpu hot-remove

[fandongdong <fandd-6gUaA8visnnQT0dZR+AlfA@public.gmane.org>]

在 2015/6/25 16:11, Jiang Liu 写道:
> 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?
Yes.
> 2) Does this issue happen if you disable irqbalance service on you
>     system?
Yes.
> 3) Has the corresponding PCI host bridge been removed before removing
>     the socket?
No, we will try to remove it before removing the socket later.
Thanks for your help, Gerry.
>
> >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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