Re: [Qemu-devel] test-filter-mirror hangs

[Jason Wang <jasowang@redhat.com>]

On 2019/1/24 下午5:11, Dr. David Alan Gilbert wrote:
> * Jason Wang (jasowang@redhat.com) wrote:
>> On 2019/1/24 上午3:53, Dr. David Alan Gilbert wrote:
>>> * Jason Wang (jasowang@redhat.com) wrote:
>>>> On 2019/1/22 上午2:56, Peter Maydell wrote:
>>>>> On Thu, 17 Jan 2019 at 09:46, Jason Wang<jasowang@redhat.com>  wrote:
>>>>>> On 2019/1/15 上午12:33, Zhang Chen wrote:
>>>>>>> On Sat, Jan 12, 2019 at 12:15 AM Dr. David Alan Gilbert
>>>>>>> <dgilbert@redhat.com  <mailto:dgilbert@redhat.com>> wrote:
>>>>>>>
>>>>>>>        * Peter Maydell (peter.maydell@linaro.org
>>>>>>>        <mailto:peter.maydell@linaro.org>) wrote:
>>>>>>>        > Recently I've noticed that test-filter-mirror has been hanging
>>>>>>>        > intermittently, typically when run on some other TCG architecture.
>>>>>>>        > In the instance I've just looked at, this was with s390x guest on
>>>>>>>        > x86-64 host, though I've also seen it on other host archs and
>>>>>>>        > perhaps with other guests.
>>>>>>>
>>>>>>>        Watch out to see if you really do see it for other guests;
>>>>>>>        it carefully avoids using virtio-net to avoid vhost; but on s390x it
>>>>>>>        uses virtio-net-ccw - could that hit the vhost it was trying to avoid?
>>>>>>>
>>>>>>>        > Below is a backtrace, though it seems to be pretty unhelpful.
>>>>>>>        > Anybody got any theories ? Does the mirror test rely on dirty
>>>>>>>        > memory bitmaps like the migration test (which also hangs
>>>>>>>        > occasionally with TCG due to some bug I'm sure we've investigated
>>>>>>>        > in the past) ?
>>>>>>>
>>>>>>>        I don't think it relies on the CPU at all.
>>>>>>>     I have no idea about this currently, but Jason and I designed the
>>>>>>> test case.
>>>>>>> Add Jason: Have any comments about this ?
>>>>>> I can't reproduce this locally with s390x-softmmu. It looks to me the
>>>>>> test should be independent to any kinds of emulation. It should pass
>>>>>> when mainloop work.
>>>>> I've just seen a hang with ppc64 guest on s390x host, so it is
>>>>> indeed not specific to s390x guest (and so not specific to
>>>>> virtio-net either, since the ppc64 guest setup uses e1000).
>>>>>
>>>>> thanks
>>>>> -- PMM
>>>> Finally reproduced locally after hundreds (sometimes thousands) times of
>>>> running.
>>>>
>>>> Bisection points to OOB monitor[1].
>>>>
>>>> It looks to me after OOB is used unconditionally we lose a barrier to make
>>>> sure socket is connected before sending packets in test-filter-mirror.c. Is
>>>> there any other similar and simple thing that we could do to kick the
>>>> mainloop?
>>> Do you mean the:
>>>
>>>       /* send a qmp command to guarantee that 'connected' is setting to true. */
>>>       qmp_discard_response(qts, "{ 'execute' : 'query-status'}");
>>
>> Yes.
>>
>>
>>> why was that ever sufficient to know the socket was ready?
>>
>> It was suggested by Fam, I don't remember the details. Can we make sure all
>> pending events has been processed (UNIX socket was set to connected) after
>> query-status is returned with an non OOB monitor?
> I'm not sure - it doesn't sound like a 'query-status' should ensure
> anything else.
> How about something like a 'query-chardev' - can that tell you what you
> need and loop until it's ready?
>
> Dave


That may work.

Thanks


>
>> Thanks
>>
>>
>>> Dave
>>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>