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

[Jason Wang <jasowang@redhat.com>]

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?

Thanks


>
> Dave
>