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[Bugfix][Multimodal] Match Qwen2.5-VL image wrappers - #57763

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Cross2pro:fix-57740-qwen25-vl-placeholder

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@Cross2pro

@Cross2pro Cross2pro commented Sep 20, 2026 •

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Summary

  • Match the complete vision wrapper (instead of the bare pad token) when expanding image and video placeholders, so a user-typed pad token in text is left untouched.
  • The wrapper target is derived per model from its own get_placeholder_str (via get_wrapper_token_ids()), not hardcoded:
    • Qwen2-VL / Qwen2.5-VL / Jina-VL: <|vision_start|><|image_pad|><|vision_end|> (official Qwen2-VL chat template is byte-identical to Qwen2.5-VL's).
    • EXAONE 4.5: <vision><|image_pad|></vision> (its tokenizer lacks <|vision_start|>, so a hardcoded lookup would raise KeyError).
    • dots.ocr: <|img|><|imgpad|><|endofimg|>.
    • OpenPangu-VL: [unused18][unused19][unused20] / [unused18][unused32][unused20] (official chat template verified).
  • Falls back to the bare pad token when the wrapper cannot be determined (e.g. Jina-VL raises for video).
  • Dummy inputs now emit the complete wrapper so profiling prompts match the new targets.
  • Qwen2.5-VL shares the parent implementation; only its EVS video-pruning logic remains via a _get_num_pad_tokens() hook.
  • Add regression tests for EXAONE/dots.ocr/Jina-style wrappers, dummy inputs, and the bare-pad-in-user-text case.

Related to #57740 (mitigates the binding mismatch but does not fully close the issue — see discussion)

Tests

  • pytest tests/models/multimodal/processing/test_qwen2_5_vl.py — 8 passed (covers Qwen2-VL, Qwen2.5-VL, EXAONE-style, dots.ocr-style, Jina-style fallback, OpenPangu-VL wrappers, and dummy inputs).
  • ruff check and ruff format --check pass on all changed files.

AI disclosure

This pull request was developed with AI assistance. The changes were reviewed and tested by the submitter.

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@Cross2pro

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Scope clarification: #57781 addresses the generic validation path by rejecting prompts whose placeholder-token occurrences exceed the recorded media placeholders. This PR addresses the Qwen2.5-VL-specific wrapper expansion and embedding-position handling.\n\nThe two changes are intended to be complementary: #57781 turns the generic mismatch into a validation error, while this PR preserves the correct Qwen2.5-VL media wrapper behavior. Please let me know if maintainers prefer these to be consolidated.

@mergify

mergify Bot commented Sep 22, 2026

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This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Cross2pro.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

@mergify mergify Bot added the needs-rebase label Sep 22, 2026
@Cross2pro
Cross2pro force-pushed the fix-57740-qwen25-vl-placeholder branch 2 times, most recently from 278dbb9 to 893aecb Compare September 22, 2026 13:03
Match the complete vision wrapper when expanding Qwen2.5-VL media placeholders, so a literal image pad token in user text cannot consume a media update. Preserve the wrapper and mark only pad tokens as embedding positions.

Fixes vllm-project#57740

Co-authored-by: OpenAI Codex <noreply@openai.com>
Signed-off-by: cross2pro <qq1091192337@gmail.com>
@Cross2pro
Cross2pro force-pushed the fix-57740-qwen25-vl-placeholder branch from 893aecb to 47eb4da Compare September 22, 2026 13:06
@Cross2pro

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Rebased onto the latest (base 362a64b) and resolved the upstream changes in . The PR is now mergeable; GitHub reports pending review/CI authorization.\n\nValidation after the rebase:\n- Qwen2.5-VL regression test: 1 passed\n- : passed\n- : passed\n- : passed\n- : passed\n\nThe test runner needed a local workaround to register the missing schema because this environment's CPU Torch/torchvision build is mismatched; the test itself passed.

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Please ignore the previous status comment; shell quoting mangled its Markdown.

Rebased onto the latest vllm-project/vllm:main (base 362a64b) and resolved the upstream changes in qwen2_5_vl.py. The PR is now mergeable; GitHub reports mergeable_state: blocked pending review/CI authorization.

Validation after the rebase:

  • Qwen2.5-VL regression test: 1 passed
  • ruff check: passed
  • ruff format --check: passed
  • compileall: passed
  • git diff --check: passed

The test runner needed a local workaround to register the missing torchvision::nms schema because this environment's CPU Torch/torchvision build is mismatched; the test itself passed.

@mergify mergify Bot removed the needs-rebase label Sep 22, 2026
@Cross2pro

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Hi @sighingnow @AndreasKaratzas @DarkLight1337 @ywang96 @vadiklyutiy — could you please add the ready label to this PR? The pre-run-check is failing because I don't have 4 merged PRs in vllm yet, so CI can't start without it. Thanks!

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Sorry for missing this, please see #57740 (comment)

@Cross2pro

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Thanks for taking a look! Just to clarify, this PR doesn't touch get_placeholder_str — the issue is in Qwen2_5_VLMultiModalProcessor._get_prompt_updates, which registers a PromptReplacement targeting the bare <|image_pad|> token. That replacement runs on the tokenized prompt, downstream of chat-template rendering, so it applies regardless of content format.

Under the 'openai' format (which Qwen2.5-VL's template indeed resolves to), a real image is rendered by the template as <|vision_start|><|image_pad|><|vision_end|>, but a user-typed literal <|image_pad|> in text tokenizes to the identical <|image_pad|> token ID. The old single-token target matches both, so user text gets expanded into a full image's worth of pad tokens — exactly the binding mismatch reported in #57740.

The fix matches the complete 3-token wrapper as the replacement target instead, so a stray <|image_pad|> in user text is left untouched (covered by the new regression test).

@DarkLight1337

DarkLight1337 commented Oct 5, 2026 •

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Your PR makes sense but it doesn't actually fix the root cause of the issue reported by #57740. Could you update your PR description to indicate that this fix is related to the issue but doesn't close that issue?

@DarkLight1337

DarkLight1337 commented Oct 5, 2026 •

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Also please check which models inherit from the Qwen2.5-VL stack, investigate whether they also use this placeholder format, and update them accordingly as well

@Cross2pro

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Thanks, I've updated the PR description to mark this as related to #57740 rather than closing it.

On the inheritance question, I checked the Qwen2.5-VL stack:

  • Qwen2-VL (Qwen2VLMultiModalProcessor, the parent class of Qwen2_5_VLMultiModalProcessor): uses the same <|vision_start|><|image_pad|><|vision_end|> wrapper with a bare-token PromptReplacement target, so it has the same issue. The fix in this PR lives in the child class, so Qwen2-VL doesn't inherit it.
  • ExaOne 4.5: its model class inherits Qwen2_5_VLForConditionalGeneration, but its processor is Qwen2VLMultiModalProcessor (aliased import), so fixing Qwen2-VL would cover it automatically.
  • OpenPangu-VL: OpenPanguVLMultiModalProcessor inherits the Qwen2.5-VL processor but overrides _get_prompt_updates with the same bare-token target pattern. Its token set differs ([unused18][unused19][unused20]-style placeholders), so it would need its own wrapper constants rather than a straight copy of this fix.
  • OpenCUA and the Omni thinkers use their own processors/tokens, so they're out of scope here.

Would you like me to extend this PR to cover Qwen2-VL (+ ExaOne 4.5) and OpenPangu-VL, or would you prefer those as follow-up PRs? Touching Qwen2-VL means changing the parent class, so I wanted to check with you first.

@DarkLight1337

DarkLight1337 commented Oct 5, 2026 •

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Yes, please do that in this PR. But make sure you have verified that the chat template of the official templates handle the placeholder tokens in the way you described

@Cross2pro

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Done — extended to Qwen2-VL (+ ExaOne 4.5, which reuses Qwen2-VL's processor) and OpenPangu-VL in c8aa3d4.

Template verification against the official checkpoints:

  • Qwen2-VL (Qwen/Qwen2-VL-7B-Instruct): chat template is byte-identical to Qwen2.5-VL's, rendering <|vision_start|><|image_pad|><|vision_end|> / <|vision_start|><|video_pad|><|vision_end|>.
  • OpenPangu-VL (FreedomIntelligence/openPangu-VL-7B): template renders [unused18][unused19][unused20] for images and [unused18][unused32][unused20] for videos, matching the wrapper tokens used in the fix (also consistent with its get_placeholder_str).

Added regression tests for both models mirroring the Qwen2.5-VL one.

…u-VL

Signed-off-by: cross2pro <qq1091192337@gmail.com>
@Cross2pro
Cross2pro force-pushed the fix-57740-qwen25-vl-placeholder branch from c8aa3d4 to 2bfdef9 Compare October 5, 2026 09:24
@DarkLight1337

DarkLight1337 commented Oct 5, 2026 •

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Codex review:

Two affected models use different wrappers, and all six affected implementations still have incompatible dummy prompts.

Qwen2-VL
Affected through: Direct change to its processor.
Image wrapper: <|vision_start|><|image_pad|><|vision_end|>
Video wrapper: <|vision_start|><|video_pad|><|vision_end|>
Result: Normal image/video prompts work. Bare-token dummy prompts fail.

Qwen2.5-VL
Affected through: Direct change to its processor.
Image wrapper: <|vision_start|><|image_pad|><|vision_end|>
Video wrapper: <|vision_start|><|video_pad|><|vision_end|>
Result: Normal image/video prompts work. Inherited bare-token dummy prompts fail.

EXAONE 4.5
Affected through: Aliases Qwen2VLMultiModalProcessor.
Image wrapper: <vision><|image_pad|></vision>
Video wrapper: <vision><|video_pad|></vision>
Result: The updated processor raises KeyError('<|vision_start|>') because that token is absent from its vocabulary. Dummy prompts also need updating.

dots.ocr
Affected through: Registers Qwen2VLMultiModalProcessor directly.
Image wrapper: <|img|><|imgpad|><|endofimg|>
Video wrapper: Unsupported.
Result: Normal image prompts fail to match the new target. Its own bare-token dummy prompts also fail.

Jina VL / jina-reranker-m0
Affected through: Its processor inherits Qwen2VLMultiModalProcessor.
Image wrapper: <|vision_start|><|image_pad|><|vision_end|>
Video wrapper: Unsupported.
Result: Normal image prompts work. Inherited bare-token dummy prompts fail.

OpenPangu-VL
Affected through: Direct change to its processor override.
Image wrapper: [unused18][unused19][unused20]
Video wrapper: [unused18][unused32][unused20]
Result: Normal image/video prompts work. Inherited bare-token dummy prompts fail

The two substantive compatibility regressions are:

  • EXAONE 4.5: its official template uses <vision> and </vision>. Its actual tokenizer vocabulary lacks <|vision_start|> and <|vision_end|>, so the PR’s new vocabulary lookup raises KeyError('<|vision_start|>') before matching. Its processor registration and placeholder method confirm the mismatch.
  • dots.ocr: it uses <|img|><|imgpad|><|endofimg|>, but the updated shared processor targets <|vision_start|><|imgpad|><|vision_end|>. Its existing Qwen vision tokens do not make these sequences equivalent. See its registration and placeholder method.

The dummy-input issue remains unresolved: the shared builder emits bare pad tokens. Qwen2.5-VL, EXAONE, Jina, and OpenPangu reuse or inherit that behavior; dots.ocr has its own bare-token override. Updating the shared builder must also handle their different wrappers.

Unaffected despite related inheritance/reuse: OpenCUA, Qwen2.5-Omni, Qwen3-Omni, and Qwen3-VL use separate prompt-update implementations. OpenCUA’s model-class inheritance does not route it through the changed processor.

I ran isolated checks (/tmp/check_pr57763.py) using the PR’s exact update methods and vLLM’s prompt-matching machinery, including multi-frame video and embedding masks. These reproduced the mismatches and dummy failures; EXAONE’s KeyError was verified against its downloaded tokenizer. This was processor-level validation, not GPU inference.

The PR needs model-specific wrapper handling for EXAONE and dots.ocr, plus compatible dummy builders and regression coverage for all six implementations.

Address review feedback: derive the prompt-replacement target from each
model class's own get_placeholder_str instead of hardcoding
<|vision_start|>/<|vision_end|>. This fixes EXAONE 4.5 (whose tokenizer
lacks those tokens and would raise KeyError) and dots.ocr (which uses
<|img|><|imgpad|><|endofimg|>), and covers Jina-VL via fallback.

- Qwen2VLMultiModalProcessor._get_prompt_updates now builds targets via
  get_wrapper_token_ids(); pad-token counting moved to an overridable
  _get_num_pad_tokens() hook so Qwen2.5-VL keeps only its EVS logic.
- Dummy inputs emit the complete wrapper so profiling prompts match.
- Regression tests for EXAONE/dots.ocr/Jina-style wrappers and dummies.

Signed-off-by: cross2pro <qq1091192337@gmail.com>
@DarkLight1337

DarkLight1337 commented Oct 5, 2026 •

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The MM processors themselves look OK overall, but M-RoPE needs to be updated accordingly with respect to the new offsets.

From codex:

Qwen2-VL
Wrapper matching: Fixed.
Dummy prompts: Fixed.
Remaining issue: Incorrect M-RoPE positions for images and videos.

Qwen2.5-VL
Wrapper matching: Fixed through the parent processor.
Dummy prompts: Fixed through inheritance.
Remaining issue: Incorrect M-RoPE positions for images and videos.

EXAONE 4.5
Wrapper matching: Fixed; uses <vision> and </vision>.
Dummy prompts: Fixed.
Previous KeyError: Resolved, verified with its actual tokenizer.
Remaining issue: Incorrect M-RoPE positions inherited from Qwen2.5-VL.

dots.ocr
Wrapper matching: Fixed; uses <|img|> and <|endofimg|>.
Dummy prompts: Fixed by removing its bare-token override.
Result: Image processor checks pass. No M-RoPE regression identified.

Jina VL / jina-reranker-m0
Image wrapper matching: Fixed.
Image dummy prompts: Fixed.
Remaining issue: Incorrect inherited M-RoPE positions.
Additional issue: Video dummy text becomes empty, although its processing info still advertises video support. Profiling with video enabled fails to match the video placeholder.

OpenPangu-VL
Wrapper matching: Fixed for images and videos.
Dummy prompts: Fixed through inheritance.
Remaining issue: Incorrect M-RoPE positions for images and videos.

The M-RoPE problem comes from the changed placeholder offset. It now points to the opening wrapper token, while the unchanged position-generation methods treat it as the first pad token. The embedding mask does not adjust that offset. I reproduced different position tensors for all five affected M-RoPE models using ordinary prompts without stray pad tokens.

The Jina problem comes from inconsistent fallbacks: get_wrapper_token_ids() falls back to a bare video pad token, but get_dummy_text() falls back to an empty string. Default profiling includes video unless its limit is explicitly set to zero.

Validation: The PR’s eight tests pass. Additional CPU checks using the actual model classes reproduced both remaining problems. No end-to-end GPU inference was run.

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GPU validation on Kaggle (Tesla T4), branch @ 062bfef8:

  • nvidia-smi → Tesla T4; git rev-parse --short HEAD → 062bfef, matches PR head.
  • Real-tokenizer wrapper checks — all passed:
    • Qwen2.5-VL image: [151652, 151655, 151653] → <|vision_start|><|image_pad|><|vision_end|>
    • Qwen2.5-VL video: [151652, 151656, 151653] → <|vision_start|><|video_pad|><|vision_end|>
    • Qwen2-VL image: [151652, 151655, 151653]
    • EXAONE-4.5: <|vision_start|> not in vocab (confirms the old hardcoded lookup would have raised KeyError); image wrapper [73, 67, 74] → <vision><|image_pad|></vision>
  • tests/models/multimodal/processing/test_qwen2_5_vl.py: 8 passed in a local CPU venv. The Kaggle runs hit notebook environment setup issues (PYTHONPATH shadowing the wheel's compiled extensions; pip mixing torch cu130 with torchaudio cu128) before reaching the tests — unrelated to this PR. A re-run with the environment fixed is in progress; I'll update here.

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Update: the environment-fixed re-run is complete.

tests/models/multimodal/processing/test_qwen2_5_vl.py: 8 passed on the Kaggle Tesla T4 machine (branch @ 062bfef), in 1.78s — on top of the real-tokenizer wrapper checks above, which also passed.

The earlier Kaggle failures were purely notebook environment setup issues on my side (PYTHONPATH shadowing the wheel's compiled extensions; pip mixing torch cu130 with torchaudio cu128), unrelated to this PR.

Comment thread vllm/model_executor/models/qwen2_vl.py Resolved
Address review follow-ups on the per-model wrapper targets:

- M-RoPE: mm_position.offset now points at the opening wrapper token
  (e.g. <|vision_start|>), while position generation expects the first
  vision token. Derive the vision-token offset from mm_position.is_embed
  via _get_vision_token_offset() and use it in iter_mm_grid_thw, restoring
  the pre-PR position semantics.
- Remove the byte-identical iter_mm_grid_thw / get_mrope_input_positions
  overrides in Qwen2.5-VL so it inherits the fixed parent implementation
  (also covering EXAONE 4.5 and Jina-VL, which share it).
- Apply the same offset fix to OpenPangu-VL's iter_mm_grid_thw.
- Jina-VL video: get_dummy_text() now falls back to the bare pad token
  when the model defines no placeholder string, consistent with the
  fallback in get_wrapper_token_ids(), so profiling with video matches
  the video replacement target.
- Regression tests: M-RoPE positions skip the wrapper prefix, the offset
  helper edge cases, and the Jina-style video dummy fallback.

Signed-off-by: cross2pro <qq1091192337@gmail.com>
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Thanks for the follow-up review — both findings were correct, fixed in acbadf2:

  • M-RoPE offsets. You were right: mm_position.offset now points at the opening wrapper token while get_mrope_input_positions treats it as the first vision token (off by one; I reproduced the shifted position tensors too). Fixed via a _get_vision_token_offset() helper that derives the first vision token's offset from mm_position.is_embed, used in iter_mm_grid_thw — this restores the exact pre-PR position semantics. Applied to Qwen2-VL (inherited by Qwen2.5-VL, EXAONE 4.5, Jina-VL) and OpenPangu-VL. Also removed Qwen2.5-VL's byte-identical iter_mm_grid_thw/get_mrope_input_positions overrides so it shares the fixed parent implementation.
  • Jina video dummy. Fixed the inconsistent fallback: get_dummy_text() now falls back to the bare pad token when the model defines no placeholder string (e.g. Jina-VL video), consistent with get_wrapper_token_ids() — this also restores the pre-PR dummy behavior there, so profiling with video matches the video replacement target.
  • Tests: 11 passed in test_qwen2_5_vl.py (8 existing + 3 new). ruff check/format clean.

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mergify Bot commented Oct 5, 2026

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This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Cross2pro.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

@mergify mergify Bot added the needs-rebase label Oct 5, 2026
@DarkLight1337

DarkLight1337 commented Oct 5, 2026 •

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It fixes several previous findings, but introduces a blocking regression:

The PR deletes Qwen2.5-VL’s implementation of get_mrope_input_positions(), apparently expecting it to inherit Qwen2-VL’s implementation.

But only the processor inherits from the Qwen2-VL processor. The Qwen2.5-VL model class does not inherit from the Qwen2-VL model class.

After deletion, calling get_mrope_input_positions() reaches the empty method in SupportsMRoPE. That method returns None.

The runner expects two values: the position tensor and its delta. When it unpacks None, it raises:

TypeError: cannot unpack non-iterable NoneType object

This blocks inference for Qwen2.5-VL and its model-class descendants, EXAONE 4.5 and OpenCUA. It affects normal requests, independently of the stray-placeholder issue this PR addresses.

The fix is to restore Qwen2.5-VL’s methods with the corrected offsets, or explicitly give it a shared implementation. The passing tests miss this because they test M-RoPE on Qwen2-VL, not Qwen2.5-VL or those descendants.

Summary

Qwen2-VL:
Wrapper matching, dummy prompts, and M-RoPE offsets pass.

Qwen2.5-VL:
Wrapper matching and dummy prompts pass.
M-RoPE now returns None instead of a position tensor and delta.

EXAONE 4.5:
Wrapper matching and dummy prompts pass.
Inherits the new Qwen2.5-VL M-RoPE failure.

dots.ocr:
Image wrapper and dummy-prompt checks pass.
No remaining regression identified in the checked paths.

Jina VL:
Image wrapper, dummy prompts, and M-RoPE offsets pass.
The video profiling fallback now matches successfully.

OpenPangu-VL:
Image/video wrappers, dummy prompts, and M-RoPE offsets pass.

OpenCUA:
Newly affected through model inheritance.
Also inherits the missing Qwen2.5-VL M-RoPE implementation, despite using an independent processor.

The previous commit wrongly deleted Qwen2.5-VL's iter_mm_grid_thw and
get_mrope_input_positions: only the processor inherits from Qwen2-VL's
processor, while Qwen2_5_VLForConditionalGeneration does not inherit from
Qwen2VLForConditionalGeneration. After deletion, M-RoPE fell back to
SupportsMRoPE's empty method returning None, breaking inference for
Qwen2.5-VL, EXAONE 4.5 and OpenCUA.

Restore both methods with the _get_vision_token_offset() correction applied,
and add a regression test covering Qwen2.5-VL's M-RoPE (previously only
Qwen2-VL was tested).

Signed-off-by: cross2pro <qq1091192337@gmail.com>
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@claude review

Resolve conflicts in qwen2_vl.py and qwen2_5_vl.py iter_mm_grid_thw:
keep upstream's data-extraction refactor, apply the M-RoPE
_get_vision_token_offset() correction on top.

Signed-off-by: cross2pro <qq1091192337@gmail.com>
@Cross2pro

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You were right — that deletion was wrong. I confused processor inheritance with model-class inheritance: only Qwen2_5_VLMultiModalProcessor inherits from Qwen2-VL's processor, while Qwen2_5_VLForConditionalGeneration does not inherit from Qwen2VLForConditionalGeneration. Falling back to SupportsMRoPE's empty method (returning None) would indeed break inference for Qwen2.5-VL, EXAONE 4.5, and OpenCUA. Fixed in c82d558:

  • Restored Qwen2.5-VL's iter_mm_grid_thw and get_mrope_input_positions with the _get_vision_token_offset() correction applied.
  • Added a regression test for Qwen2.5-VL's M-RoPE (you were right that the tests only covered Qwen2-VL) — this also covers EXAONE 4.5/OpenCUA via model-class inheritance.

Also resolved the merge conflicts with upstream/main (kept upstream's data-extraction refactor in iter_mm_grid_thw, applied the offset correction on top) — the PR is mergeable again.

Tests: 12 passed in test_qwen2_5_vl.py. ruff check/format clean.

@mergify mergify Bot removed the needs-rebase label Oct 5, 2026

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Code review found no issues

No high-confidence issues detected in this change.

This review covers commit c82d558, which is no longer the latest commit on this pull request; later commits are not covered by it.

Per review feedback, avoid the model_loader.get_model_cls indirection in
OpenPanguVLMultiModalProcessor._get_prompt_updates. Reference
OpenPanguVLForConditionalGeneration directly (defined in the same file)
when deriving wrapper token ids.

Signed-off-by: cross2pro <qq1091192337@gmail.com>
Comment thread vllm/model_executor/models/qwen2_vl.py Resolved
Per review feedback, avoid the model_loader.get_model_cls indirection.
Processors and dummy builders now expose the model class via an explicit
_get_model_cls() method: the Qwen2-VL base returns Qwen2VLForConditionalGeneration,
and each subclass (Qwen2.5-VL, Jina, EXAONE 4.5, dots.ocr, OpenPangu) overrides it
with its own model class. EXAONE 4.5 and dots.ocr get dedicated processor
subclasses instead of aliasing the base directly.

Signed-off-by: cross2pro <qq1091192337@gmail.com>
vocab = tokenizer.get_vocab()

model_cls = get_model_cls(self.info.ctx.model_config)
model_cls = self._get_model_cls()

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Can we just extract the tokens from hf_processor instead of the model class?

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Good question — I checked, and hf_processor doesn't have the full wrapper. Qwen2VLProcessor only exposes image_token (<|image_pad|>) and video_token (<|video_pad|>); the surrounding <|vision_start|>/<|vision_end|> (or <vision>/</vision>, <|img|>/<|endofimg|>, [unused18]/[unused20]) are emitted by the chat template, not stored on the processor object. That's exactly why the model class's get_placeholder_str exists in vLLM — it's the explicit record of what each model's template emits, which is what we need to match. Deriving it from the template at runtime (e.g. applying it to a dummy message and parsing) would be fragile; the per-model placeholder string is the ground truth we already maintain.

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Then in that case, it seems that the HF processor doesn't actually consider <|vision_start|> and <|vision_end|> to be part of the replacement tokens. We should try to follow the conventions from HF Transformers

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I see the concern, but there's a structural reason: in vLLM, _get_prompt_updates runs after the chat template has been applied, so the prompt already contains the full wrapper (<|vision_start|><|image_pad|><|vision_end|>). If the replacement were just the pads (following HF's processor convention), the vs/ve tokens in the target would be deleted from the prompt, which the model doesn't expect.

HF can keep vs/ve out of the processor's replacement because the template adds them afterwards. vLLM does it in the opposite order: template first, then prompt replacement to expand the pads. Matching the full wrapper as the target is what lets us distinguish a template-emitted placeholder from a bare pad token typed by the user (the #57740 mitigation) — with a pads-only target we'd be back to the original bug.

If you're suggesting we move vLLM's replacement to pre-template (HF's order), that's a much larger architectural change — happy to discuss it separately, but it's out of scope for this mitigation PR. Does the current approach work for you?

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We consider HF as the reference implementation. If you feel that this is something that needs to be fixed, perhaps it would be more approprate to fix on HF upstream first?

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I agree HF is the reference, and this PR doesn't diverge from it — it doesn't change what tokens the model receives, only which token sequences vLLM's prompt replacement treats as placeholders.

The issue #57740 is vLLM-specific: it comes from vLLM's _get_prompt_updates, which has no equivalent in HF Transformers. HF never needs to distinguish "template-emitted placeholder" from "user-typed pad token" because HF doesn't do post-template prompt replacement. So there's nothing to fix on HF upstream for this — the fix (or mitigation) has to live in vLLM.

The wrapper matching doesn't invent new tokens or change HF's conventions; it just narrows vLLM's match target from the bare pad (which collides with user text) to the full template-emitted wrapper. The model still receives exactly the same tokens as before.

If you'd rather not take this mitigation approach at all, I'm happy to close the PR — just let me know which direction you'd prefer.

@DarkLight1337 DarkLight1337 Oct 5, 2026 •

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We would like our search/replace to be based on the HF code. As I mentioned in the original issue, I'd prefer the mitigation to be done on the client side: vLLM shouldn't reject input that is considered valid for HF Transformers - even if incorrect model behavior occurs because of the limited validation from HF Transformers, it's not our job to enforce further validation on top of what HF provides.

- Preserve the original per-frame video replacement layout ([1:-1] stripping
  outer wrapper tokens) in OpenPanguVLMultiModalProcessor; the PR only changes
  the match target, not the replacement token arrangement.
- OpenPanguVLDummyInputsBuilder now resolves to OpenPanguVLForConditionalGeneration
  (its placeholder strings differ from Qwen2.5-VL's).

Signed-off-by: cross2pro <qq1091192337@gmail.com>
@Cross2pro

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Closing per your feedback — I understand the position that vLLM shouldn't add server-side validation beyond HF. Thanks for the detailed reviews; the discussion is recorded here for reference.

@Cross2pro Cross2pro closed this Oct 5, 2026
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