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[Bugfix][Model][CI/Build] Fix CUDA graph capture in GLM-OCR / GLM4-MoE-Lite MTP layers - #51966

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[Bugfix][Model][CI/Build] Fix CUDA graph capture in GLM-OCR / GLM4-MoE-Lite MTP layers#51966
bulatovv wants to merge 2 commits into
vllm-project:mainfrom
bulatovv:fix/glm-ocr-mtp-cudagraph-capture

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Purpose

FIX #48749

GlmOcrMultiTokenPredictorLayer.forward and Glm4MoeLiteMultiTokenPredictorLayer.forward
mask the position-0 embedding with an in-place boolean-mask assignment:

inputs_embeds[positions[0] == 0] = 0     # glm_ocr_mtp.py
inputs_embeds[positions == 0] = 0        # glm4_moe_lite_mtp.py

A boolean-mask index_put_ calls nonzero(), whose output shape is data-dependent, so it
synchronizes device to host to size the allocation. That is not allowed inside an active
CUDA graph capture, and the V2 model runner captures the MTP prefill graph
(speculator.capture() -> prefill_cudagraph_manager.capture()), so engine startup fails:

File "vllm/model_executor/models/glm_ocr_mtp.py", line 87, in forward
    inputs_embeds[positions[0] == 0] = 0
torch.AcceleratorError: CUDA error: operation not permitted when stream is capturing

It was reported on A100-SXM4-80GB in #48749.

The equivalent capture-safe form is already used by the other two MTP implementations:

  • vllm/model_executor/models/deepseek_mtp.py:113
  • vllm/model_executor/models/glm4_moe_mtp.py:113

both of which read inputs_embeds = torch.where(positions.unsqueeze(-1) == 0, 0, inputs_embeds).
This PR applies the same form to the two remaining implementations. GLM-OCR keeps
positions[0] because it is an MRoPE model, where positions has shape (3, seq_len).

Duplicate-work checks were performed before opening: no open PR references #48749 or
touches glm_ocr_mtp.py. #39483 and #43747 fix different code paths that surface the same
CUDA error.

Related: #49869 fixes an unrelated GLM-OCR MTP weight-loading regression (#49856). On main
as of 3ee2df3 with the HF checkpoint, startup fails there before reaching graph capture,
so that patch was applied locally to reproduce this crash. The crash fixed here reproduces
with no local patches on v0.25.1. The two fixes are independent and can merge in either
order.

Test Plan

Adds a GLM-OCR entry to tests/v1/e2e/spec_decode/mtp/test_mtp.py, covering engine startup
and CUDA graph capture with MTP for this model.

The entry will fail in CI until #49869 lands, because GLM-OCR MTP weights fail to load
(#49856) and the engine dies before reaching graph capture. It was run locally with that
patch applied, before and after the fix:

pytest "tests/v1/e2e/spec_decode/mtp/test_mtp.py::test_mtp_correctness[glm_ocr]"

Test Result

Environment Before After
3ee2df3, RTX 2080 Ti (sm75), torch 2.13.0+cu130, #49869 applied locally so MTP weights load e2e test fails: cudaErrorStreamCaptureUnsupported at glm_ocr_mtp.py:87 while capturing prefill FULL graphs e2e test passes; exact text matches=100/100
0.25.1, Tesla T4 (sm75), CUDA 12.9, num_speculative_tokens: 3 engine dies during startup capture (traceback in #48749) starts; captures prefill 51/51 PIECEWISE and 49/49 FULL, decode 35/35 FULL; serves; OCRs a document block correctly

pre-commit: all hooks passed on the three changed files.

AI assistance

AI assistance was used to investigate the stream-capture failure, implement this change,
run validation, and prepare this PR.

bulatovv and others added 2 commits August 11, 2026 22:37
… layers

The MTP layers masked position-0 embeddings with an in-place boolean-mask
assignment. Boolean-mask index_put_ calls nonzero(), which syncs device to
host to size its output, and that is illegal during CUDA graph capture. The
V2 model runner captures the MTP prefill graph, so engine startup died with
cudaErrorStreamCaptureUnsupported.

Use the capture-safe torch.where form already used by deepseek_mtp.py and
glm4_moe_mtp.py. GLM-OCR keeps its existing positions[0] indexing: it is an
MRoPE model, so positions has shape (3, seq_len) rather than (seq_len,).

FIX vllm-project#48749

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Albert Fazlyev <albert.fz@yandex.ru>
Covers the CUDA graph capture crash fixed in the previous commit: without it
the entry dies at glm_ocr_mtp.py while capturing prefill FULL graphs.

The entry runs text-only with limit_mm_per_prompt zeroed, matching the
Qwen3.5 and gemma-4 entries, and uses a 0.0 accuracy threshold because GSM8k
is not meaningful for an OCR model; correctness is asserted by matching the
speculative output against the non-speculative reference.

This entry cannot pass on main until vllm-project#49869 lands: GLM-OCR MTP weights fail
to load (vllm-project#49856), so the engine dies before graph capture is reached.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Albert Fazlyev <albert.fz@yandex.ru>

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[Bug]: [MRV2] MTP speculative decoding crashes with cudaErrorStreamCaptureUnsupported during CUDA graph capture

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