[AMD] [CI] Fix tests for v0.28.0 (#6830)

Signed-off-by: tjtanaa <tunjian.tan@embeddedllm.com>

tests/diffusion/attention/test_flash_attn.py

@@ -353,8 +353,15 @@ def test_cross_attn_key_padding_vs_sdpa(k_len):
     print(f"Max absolute difference: {max_diff:.6f}")
     print(f"Mean absolute difference: {mean_diff:.6f}")
 
-    assert max_diff < 0.01, f"Max difference {max_diff} exceeds threshold 0.01"
-    assert mean_diff < 0.001, f"Mean difference {mean_diff} exceeds threshold 0.001"
+    # Match the platform-specific comparison used by test_fa_vs_sdpa above.
+    if current_omni_platform.is_rocm():
+        # AITER FlashAttention and PyTorch SDPA use different BF16 reduction
+        # implementations on ROCm, so individual values can differ by one BF16
+        # step even though the outputs agree within the expected relative error.
+        torch.testing.assert_close(output_fa, output_sdpa, rtol=1e-2, atol=1.5e-2)
+    else:
+        assert max_diff < 0.01, f"Max difference {max_diff} exceeds threshold 0.01"
+        assert mean_diff < 0.001, f"Mean difference {mean_diff} exceeds threshold 0.001"
 
     print("✓ Case 3 PASSED: FA and SDPA cross-attention outputs are very close!")
 

tests/diffusion/conftest.py

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+import torch
+
+
+@pytest.fixture(autouse=True)
+def restore_torch_default_dtype():
+    """Keep process-global dtype changes from leaking between diffusion tests."""
+    default_dtype = torch.get_default_dtype()
+    try:
+        yield
+    finally:
+        torch.set_default_dtype(default_dtype)