Re: [BUG] kernel BUG at drivers/block/xen-blkfront.c:1711

From: Evgenii Shatokhin <eshatokhin@virtuozzo.com>
To: George Dunlap <george.dunlap@citrix.com>
Cc: Juergen Gross <jgross@suse.com>,
	Dario Faggioli <dario.faggioli@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	David Vrabel <david.vrabel@citrix.com>,
	Konstantin Khorenko <khorenko@virtuozzo.com>,
	Roger Pau Monne <roger.paumonne@citrix.com>
Subject: Re: [BUG] kernel BUG at drivers/block/xen-blkfront.c:1711
Date: Mon, 11 Jul 2016 17:34:23 +0300	[thread overview]
Message-ID: <5783AE6F.5070702@virtuozzo.com> (raw)
In-Reply-To: <CAFLBxZZErHfTq=e1d9w5wxRe0=gYFnhiS81c43DZM1id6QCHhQ@mail.gmail.com>

On 11.07.2016 13:37, George Dunlap wrote:
> On Mon, Jul 11, 2016 at 9:50 AM, Evgenii Shatokhin
> <eshatokhin@virtuozzo.com> wrote:
>> On 06.06.2016 11:42, Dario Faggioli wrote:
>>>
>>> Just Cc-ing some Linux, block, and Xen on CentOS people...
>>>
>>
>> Ping.
>>
>> Any suggestions how to debug this or what might cause the problem?
>>
>> Obviously, we cannot control Xen on the Amazon's servers. But perhaps there
>> is something we can do at the kernel's side, is it?
>
> I think part of the problem is that your report has confused people so
> that everyone cc'd thinks it's someone else's problem. :-)
>
> To wit..
>
>>>> One of our users gets kernel panics from time to time when he tries
>>>> to
>>>> use his Amazon EC2 instance with CentOS7 x64 in it [1]. Kernel panic
>>>> happens within minutes from the moment the instance starts. The
>>>> problem
>>>> does not show up every time, however.
>>>>
>>>> The user first observed the problem with a custom kernel, but it was
>>>> found later that the stock kernel 3.10.0-327.18.2.el7.x86_64 from
>>>> CentOS7 was affected as well.
>
> ...by mentioning the exact CentOS kernel version, but not the version
> of the "custom kernel" you used, I suspect the people familiar with
> netfront filtered this out as something to be taken care of by the
> CentOS / RHEL system.

The custom kernel is based on the same RHEL's kernel 
3.10.0-327.18.2.el7.x86_64 as the one from CentOS 7. We did not change 
Xen-related parts there.

>
> If you can reproduce this with a relatively recent stock kernel,
> please post the kernel version and the debug information.
>
> If you can't, then it's likely to be an issue that RH needs to take
> care of by backporting whatever change fixed the issue.

Thanks for the suggestion.

Yes, if the patch Bob Liu has proposed does not help, I will try to 
reproduce the problem on a recent mainline kernel.

The difficult part is that the problem is rather hard to reproduce, but, 
well, it is another story.

>
> Thanks,
>   -George
> .
>

Regards,
Evgenii

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