[Bug Skip]: test_activation_checkpointing_xpu.test_ac_rematerialize_with_sdpa_dropout_zero failed with error DumpError: can't serialize <class 'torch.nn.attention._SDPBackend'

[shangerxin]

🐛 Describe the bug with skip template

third_party.torch-xpu-ops.test.xpu.dynamo.test_activation_checkpointing_xpu.RematerializeACNodesPassTests::test_ac_rematerialize_with_sdpa_dropout_zero failed because the test runner could not serialize a torch.nn.attention._SDPBackend object while reporting a subtest result through pytest-xdist.

The actual failure is not from the test assertion itself, but from test infrastructure during result reporting. While pytest_subtests and xdist were sending the subtest report from the worker process, Python serialization raised:

DumpError: can't serialize <class 'torch.nn.attention._SDPBackend'>

This indicates the subtest failure metadata or attached exception context included an _SDPBackend value that cannot be pickled/serialized for transport between processes. As a result, the test run aborts with an infrastructure serialization error instead of a normal test failure report.

Short version for an issue template:

The test test_ac_rematerialize_with_sdpa_dropout_zero fails in test reporting, not necessarily in model logic. pytest-xdist cannot serialize torch.nn.attention._SDPBackend when emitting a subtest report, causing DumpError: can't serialize <class 'torch.nn.attention._SDPBackend'>. This appears to be a test infrastructure / serialization issue involving subtest result payloads.

Versions

XPU PR

#4894

Versions

Version context from report: pytorch main 2.15.0a0
pytorch main 2.15.0a0

[shangerxin]

Duplicated