test: add nan/inf clamp regression test for fused_topk_bias

[jhaotingc]

Add test_fused_topk_bias_nan_inf_clamp to cover the same NaN/Inf scenario as test_fused_topk_nan_inf_clamp but for the fused_topk_bias entry point. On CUDA, fused_topk_bias routes through the same topk_softmax/topk_sigmoid kernels fixed in #39391 (lines 131/154 of topk_softmax_kernels.cu), so the clamp already applies.

Closes #40457

Purpose

PR #39391 fixed NaN/Inf gating logits producing duplicate expert IDs in fused_topk by clamping scores to 0 in topk_softmax_kernels.cu (lines 131/154 for the warp-level path, line 457 for the fallback path). However,
the regression test added in that PR only covered fused_topk. This PR adds the same nan/inf regression test for fused_topk_bias, which is used by DeepSeek-style models with e_score_correction_bias.

On CUDA, fused_topk_bias routes through the same topk_softmax / topk_sigmoid C++ kernels that were patched in #39391, so the clamp already applies. This PR confirms that coverage with an explicit test.

Test Plan

• Added test_fused_topk_bias_nan_inf_clamp to
  tests/kernels/moe/test_fused_topk.py, parametrized over:
  • dtype: bfloat16, float16, float32
  • scoring_func: softmax, sigmoid
  • bad_value: NaN, Inf
  • num_experts: 6, 8, 16
  • topk: 3, 4
  • Total: 144 test cases
• Verified the test is automatically collected by the existing
  Kernels MoE Test CI step (no .buildkite/ changes needed):

  # Simulate exactly what buildkite runs:
  pytest tests/kernels/moe --collect-only -q | grep nan_inf
  # Shows both test_fused_topk_nan_inf_clamp (added in #39391) and
  # test_fused_topk_bias_nan_inf_clamp (this PR) are collected

• Ran the full test_fused_topk.py suite (720 tests) to check for regressions.

Test Result

nan/inf regression tests (144 cases)

Kernel clamp	nan/inf tests passed	nan/inf tests failed
Disabled (pre-#39391 behaviour)	36	108
Enabled (post-#39391, this PR)	144	0

Full test suite (720 cases, 2×H200, CUDA 13.0)

720 passed, 16 warnings in 104.91s

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[jhaotingc]

@claude review

[jhaotingc]

cc @vadiklyutiy

[gemini-code-assist]

Code Review

This pull request adds a regression test for the fused_topk_bias kernel to ensure that NaN or Inf values in gating logits do not lead to duplicate expert IDs or non-finite weights when expert score correction bias is present. I have no feedback to provide as there were no review comments.

[vadiklyutiy]

I think we also should add this test to CI. I don't see the tests name or corresponding dir in .buildkite

[jhaotingc]

I think we also should add this test to CI. I don't see the tests name or corresponding dir in .buildkite

Verified the test is automatically collected by the existing Kernels MoE Test CI step (no .buildkite/ changes needed):

# Simulate exactly what buildkite runs:
pytest tests/kernels/moe --collect-only -q | grep nan_inf
# Shows both test_fused_topk_nan_inf_clamp (added in #39391) and
# test_fused_topk_bias_nan_inf_clamp (this PR) are collected

Does this suffice? I'm not familiar with VLLM CI. Thanks.

[jhaotingc]

https://github.com/vllm-project/vllm/blob/main/.buildkite/test_areas/kernels.yaml#L66

[vadiklyutiy]

Does this suffice? I'm not familiar with VLLM CI. Thanks.

Oops, missed it. All good.