Re: [RESEND][BUG FIX HELP] QEMU main thread endlessly hangs in __ppoll()

[John Snow <jsnow@redhat.com>]

On 3/4/21 10:08 PM, Like Xu wrote:
> Hi John,
> 
> Thanks for your comment.
> 
> On 2021/3/5 7:53, John Snow wrote:
>> On 2/28/21 9:39 PM, Like Xu wrote:
>>> Hi Genius,
>>>
>>> I am a user of QEMU v4.2.0 and stuck in an interesting bug, which may 
>>> still exist in the mainline.
>>> Thanks in advance to heroes who can take a look and share understanding.
>>>
>>
>> Do you have a test case that reproduces on 5.2? It'd be nice to know 
>> if it was still a problem in the latest source tree or not.
> 
> We narrowed down the source of the bug, which basically came from
> the following qmp usage:
> 
> {'execute': 'human-monitor-command', 'arguments':{ 'command-line': 
> 'drive_del replication0' } }
> 
> One of the test cases is the COLO usage (docs/colo-proxy.txt).
> 
> This issue is sporadic,the probability may be 1/15 for a io-heavy guest.
> 
> I believe it's reproducible on 5.2 and the latest tree.
> 

Can you please test and confirm that this is the case, and then file a 
bug report on the LP: https://launchpad.net/qemu and include:

- The exact commit you used (current origin/master debug build would be 
the most ideal.)
- Which QEMU binary you are using (qemu-system-x86_64?)
- The shortest command line you are aware of that reproduces the problem
- The host OS and kernel version
- An updated call trace
- Any relevant commands issued prior to the one that caused the hang; or 
detailed reproduction steps if possible.

Thanks,
--js