Re: [PATCH v2 0/2] virtio-gpu: Do not wait for the main thread during reset

["Alex Bennée" <alex.bennee@linaro.org>]

Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp> writes:

> On 2026/05/19 4:35, Alex Bennée wrote:
>> Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp> writes:
>> 
>>> This fixes a deadlock I previously observed with the test in [1].
>>>
>>> However, I can no longer reproduce the issue reliably with that test, so
>>> I used Codex, a coding agent, to write a more reliable local test case,
>>> shown below. I applied to Codex for Open Source to get access. The test
>>> case is not intended for merge: current policy prohibits that, and it is
>>> probably not worth carrying anyway because race-condition tests are
>>> inherently fragile.
>> What sort of hit rate where you getting with the race? So far they
>> have
>> both been rock solid without the additional patches for me.
>
> I hit the deadlock in 8 out of 10 trials.

It's taking a lot longer on my system (~ 1 in 100) but with these
patches I'm still seeing a hang, it just takes a lot longer to get
there.

>
>> 
>>> The remaining patches were written by me.
>>>
>>> [1] https://lore.kernel.org/qemu-devel/20251014111234.3190346-9-alex.bennee@linaro.org/
>>>
>>> To: qemu-devel@nongnu.org
>>> Cc: Alex Bennée <alex.bennee@linaro.org>
>>> Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>> Cc: Michael S. Tsirkin <mst@redhat.com>
>>> Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
>>>
>>> Below is the Codex-written test case:
>>>
>>> diff --git a/tests/functional/aarch64/test_gpu_blob.py b/tests/functional/aarch64/test_gpu_blob.py
>>> index a913d3b29c84..52627b4541f9 100755
>>> --- a/tests/functional/aarch64/test_gpu_blob.py
>>> +++ b/tests/functional/aarch64/test_gpu_blob.py
>>> @@ -13,7 +13,9 @@
>>>   #
>>>   # SPDX-License-Identifier: GPL-2.0-or-later
>>>   -from qemu.machine.machine import VMLaunchFailure
>>> +import subprocess
>>> +
>>> +from qemu.machine.machine import AbnormalShutdown, VMLaunchFailure
>>>     from qemu_test import Asset
>>>   from qemu_test import wait_for_console_pattern
>>> @@ -25,8 +27,7 @@ class Aarch64VirtBlobTest(LinuxKernelTest):
>>>                          'download?path=%2Fblob-test&files=qemu-880.bin',
>>>                          '2f6ab85d0b156c94fcedd2c4c821c5cbd52925a2de107f8e2d569ea2e34e42eb')
>>>   -    def test_virtio_gpu_blob(self):
>>> -
>>> +    def launch_blob_test(self):
>>>           self.set_machine('virt')
>>>           self.require_accelerator("tcg")
>>>   @@ -65,9 +66,27 @@ def test_virtio_gpu_blob(self):
>>>                   self.log.info("unhandled launch failure: %s", excp.output)
>>>                   raise excp
>>>   +    def test_virtio_gpu_blob(self):
>>> +        self.launch_blob_test()
>>> +
>>>           self.wait_for_console_pattern('[INFO] virtio-gpu test finished')
>>>           # the test should cleanly exit
>>>   +    def test_virtio_gpu_blob_shutdown_race(self):
>>> +        self.launch_blob_test()
>>> +
>>> +        self.wait_for_console_pattern('[INFO] unmapping blob object resource')
>>> +
>>> +        try:
>>> +            self.vm.shutdown(timeout=10)
>>> +        except AbnormalShutdown as excp:
>>> +            if isinstance(excp.__cause__, subprocess.TimeoutExpired):
>>> +                raise AssertionError(
>>> +                    "QEMU failed to exit while virtio-gpu reset was racing "
>>> +                    "with shutdown") from excp
>>> +            self.log.info("QEMU exited before the shutdown request completed: %s",
>>> +                          excp)
>>> +
>>>     if __name__ == '__main__':
>>>       LinuxKernelTest.main()
>>>
>>> ---
>>> Changes in v2:
>>> - Added the patch "virtio-gpu: Run reset cleanup in the same BH".
>>> - My assumption about the ordering was incorrect, so I changed the patch
>>>    to follow the approach used by virtio-gpu-gl.
>>> - Link to v1: https://lore.kernel.org/qemu-devel/20251029-gpu-v1-1-e3e3c7eebc9e@rsg.ci.i.u-tokyo.ac.jp
>>>
>>> ---
>>> Akihiko Odaki (2):
>>>        virtio-gpu: Run reset cleanup in the same BH
>>>        virtio-gpu: Do not wait for the main thread during reset
>>>
>>>   include/hw/virtio/virtio-gpu.h |  4 +--
>>>   hw/display/virtio-gpu.c        | 60 ++++++++++++++++++++----------------------
>>>   2 files changed, 30 insertions(+), 34 deletions(-)
>>> ---
>>> base-commit: 14f38a63b9adc02c0ebe3b5ada1f1208abaf21ea
>>> change-id: 20251029-gpu-c3f45747f7ba
>>>
>>> Best regards,
>> 

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro