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:

> 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.


> 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