Re: [Qemu-devel] [ceph-users] qemu-1.4.0 and onwards, linux kernel 3.2.x, ceph-RBD, heavy I/O leads to kernel_hung_tasks_timout_secs message and unresponsive qemu-process, [Bug 1207686]

[Oliver Francke <Oliver.Francke@filoo.de>]

Hi Josh,

just opened

http://tracker.ceph.com/issues/5919

with all collected information incl. debug-log.

Hope it helps,

Oliver.

On 08/08/2013 07:01 PM, Josh Durgin wrote:
> On 08/08/2013 05:40 AM, Oliver Francke wrote:
>> Hi Josh,
>>
>> I have a session logged with:
>>
>>      debug_ms=1:debug_rbd=20:debug_objectcacher=30
>>
>> as you requested from Mike, even if I think, we do have another story
>> here, anyway.
>>
>> Host-kernel is: 3.10.0-rc7, qemu-client 1.6.0-rc2, client-kernel is
>> 3.2.0-51-amd...
>>
>> Do you want me to open a ticket for that stuff? I have about 5MB
>> compressed logfile waiting for you ;)
>
> Yes, that'd be great. If you could include the time when you saw the 
> guest hang that'd be ideal. I'm not sure if this is one or two bugs,
> but it seems likely it's a bug in rbd and not qemu.
>
> Thanks!
> Josh
>
>> Thnx in advance,
>>
>> Oliver.
>>
>> On 08/05/2013 09:48 AM, Stefan Hajnoczi wrote:
>>> On Sun, Aug 04, 2013 at 03:36:52PM +0200, Oliver Francke wrote:
>>>> Am 02.08.2013 um 23:47 schrieb Mike Dawson <mike.dawson@cloudapt.com>:
>>>>> We can "un-wedge" the guest by opening a NoVNC session or running a
>>>>> 'virsh screenshot' command. After that, the guest resumes and runs
>>>>> as expected. At that point we can examine the guest. Each time we'll
>>>>> see:
>>> If virsh screenshot works then this confirms that QEMU itself is still
>>> responding.  Its main loop cannot be blocked since it was able to
>>> process the screendump command.
>>>
>>> This supports Josh's theory that a callback is not being invoked.  The
>>> virtio-blk I/O request would be left in a pending state.
>>>
>>> Now here is where the behavior varies between configurations:
>>>
>>> On a Windows guest with 1 vCPU, you may see the symptom that the 
>>> guest no
>>> longer responds to ping.
>>>
>>> On a Linux guest with multiple vCPUs, you may see the hung task message
>>> from the guest kernel because other vCPUs are still making progress.
>>> Just the vCPU that issued the I/O request and whose task is in
>>> UNINTERRUPTIBLE state would really be stuck.
>>>
>>> Basically, the symptoms depend not just on how QEMU is behaving but 
>>> also
>>> on the guest kernel and how many vCPUs you have configured.
>>>
>>> I think this can explain how both problems you are observing, Oliver 
>>> and
>>> Mike, are a result of the same bug.  At least I hope they are :).
>>>
>>> Stefan
>>
>>
>


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Oliver Francke

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