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

Mon, 18 May 2026 23:31:23 -0700 

On 2026/05/19 4:35, Alex Bennée wrote:

Akihiko Odaki <[email protected]> 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.





The remaining patches were written by me.

[1] 
https://lore.kernel.org/qemu-devel/[email protected]/

To: [email protected]
Cc: Alex Bennée <[email protected]>
Cc: Dmitry Osipenko <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Signed-off-by: Akihiko Odaki <[email protected]>

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/[email protected]

---
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,

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