[Bugfix] Avoid nested rerank cancellation handlers by migarci2 · Pull Request #55602 · vllm-project/vllm

migarci2 · 2026-09-06T18:30:55Z

Summary

The /v1/rerank and /v2/rerank aliases passed the same request to the already decorated /rerank handler. That created two concurrent consumers of raw_request.receive() and could leave the real rerank handler running after disconnect.

This removes the redundant outer cancellation decorators. Each alias now relies on the canonical /rerank handler, so every request has one disconnect listener.

I checked issue #55502 and searched open PRs for the issue number and rerank cancellation before updating this. I found no duplicate.

Testing

Targeted pytest for tests/entrypoints/pooling/scoring/test_api_router.py: 2 passed
Pre-commit hooks for the affected files: all passed
The regression fails for both aliases with the old nested decorators and passes after this change

No model evaluation was run because this only removes duplicate request-disconnect listeners and does not affect model output.

AI assistance was used to help investigate, implement, test, and review this change.

Fixes #55502

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coderabbitai · 2026-09-06T18:32:08Z

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Reviewing files that changed from the base of the PR and between c284200 and 00c1377.

📒 Files selected for processing (2)

tests/entrypoints/pooling/scoring/test_api_router.py
vllm/entrypoints/pooling/scoring/api_router.py

💤 Files with no reviewable changes (1)

vllm/entrypoints/pooling/scoring/api_router.py

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📝 Summary

Summary by CodeRabbit

Bug Fixes
- Improved reliability for rerank requests when clients disconnect.
- Rerank aliases now complete cleanly without duplicate disconnect handling or unnecessary server load changes.
- The /score, /v1/score, and /rerank endpoints continue to operate as before.

Walkthrough

The rerank v1 and v2 handlers no longer use with_cancellation. A parametrized async test verifies disconnect behavior for both aliases.

Changes

Rerank cancellation

Layer / File(s)	Summary
Rerank handler cancellation and regression coverage `vllm/entrypoints/pooling/scoring/api_router.py`, `tests/entrypoints/pooling/scoring/test_api_router.py`	The `do_rerank_v1` and `do_rerank_v2` handlers no longer use `with_cancellation`. The test simulates a disconnect and checks handler cancellation, route completion, one receive call, and unchanged server load metrics.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 00c13

The v1 and v2 rerank aliases now avoid duplicate disconnect listeners while retaining cancellation through the shared handler. Regression coverage verifies the expected disconnect behavior for both routes, with no remaining merge-blocking risk.

Suggested reviewers: taneem-ibrahim

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 10.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 10 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the bug fix: it removes nested rerank cancellation handlers. This matches the primary code and test changes.
Description check	✅ Passed	The description explains the redundant cancellation decorators, the resulting disconnect-listener issue, the fix, testing, and linked issue `#55502`. It directly matches the changeset.
Linked Issues check	✅ Passed	The changes address issue `#55502` by ensuring the rerank aliases use one cancellation handler and one disconnect listener. The regression test verifies cancellation behavior for both aliases, including…
Out of Scope Changes check	✅ Passed	The pull request contains only changes related to rerank cancellation handling and its regression test. No unrelated code or scope was identified.

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✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

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github-actions · 2026-09-06T18:41:32Z

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taneem-ibrahim · 2026-09-07T16:19:45Z

+            if handler_task in done:
+                return handler_task.result()
+            return None
+        finally:


This changes cancellation semantics for every decorated endpoint, while the asserted root cause is redundant cancellation wrappers on the rerank aliases. Those aliases still create two concurrent consumers of the same raw_request.receive(). Could we instead remove the redundant outer decorators from the aliases so each request has exactly one disconnect listener?

Good point. I removed the redundant decorators from /v1/rerank and /v2/rerank, so the shared request now has one disconnect listener.

taneem-ibrahim · 2026-09-07T16:21:27Z

+
+    @with_cancellation
+    async def alias(payload, raw_request):
+        return await handler(payload, inner_request)


The real /v1/rerank and /v2/rerank aliases pass the same raw_request to the already-decorated handler. This test instead gives the wrappers independent request objects and independent disconnect streams, so it misses the competing receive() consumers and possible duplicate load-counter updates. Please reproduce the actual alias topology using one request.

Updated. The regression now calls both real aliases with the same request and checks one receive() call, handler cancellation, and a balanced load counter.

taneem-ibrahim · 2026-09-07T16:23:04Z

+                task.cancel()
+            cleanup = asyncio.gather(*tasks, return_exceptions=True)
+            cancelled = False
+            while not cleanup.done():


This makes the route task resistant to every subsequent cancellation until both children terminate. A handler that delays or suppresses CancelledError can therefore block timeouts or server shutdown indefinitely. Please bound the cleanup wait or avoid the global behavior change by removing the redundant alias wrappers.

Agreed. The shared helper is back to its original behavior, and the fix is now limited to the redundant rerank alias wrappers.

taneem-ibrahim · 2026-09-07T16:23:44Z

+        finally:
+            for task in tasks:
+                task.cancel()
+            cleanup = asyncio.gather(*tasks, return_exceptions=True)


return_exceptions=True retrieves and then silently discards non-cancellation failures raised during handler cleanup. That can hide an engine-abort failure and leave work running without diagnostics. Please propagate or at least log cleanup exceptions other than CancelledError.

Agreed. That cleanup path is gone with the global helper change, so this patch no longer swallows cleanup exceptions.

Remove redundant cancellation decorators from the v1 and v2 rerank aliases so the shared request has one disconnect listener. Assisted-by: AI coding assistant Signed-off-by: Miguel Garcia <miguelgarciaroman8@gmail.com>

noooop · 2026-09-08T00:52:07Z

@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: Apache-2.0


Thanks for your contribution.

I don't think we really need this test.

hi @migarci2 , I agree with @noooop . We don't need to add another additional test for this change. Can you please remove this?

migarci2 · 2026-09-14T21:31:08Z

Friendly bump — earlier feedback is addressed and this has an approval. Happy to drop the regression test if preferred. Ready whenever you have a moment.

taneem-ibrahim · 2026-09-14T22:01:01Z

@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: Apache-2.0


hi @migarci2 , I agree with @noooop . We don't need to add another additional test for this change. Can you please remove this?

Signed-off-by: Miguel Garcia <miguelgarciaroman8@gmail.com>

migarci2 · 2026-09-14T22:03:23Z

Thanks @taneem-ibrahim — removed tests/entrypoints/pooling/scoring/test_api_router.py as requested. The fix is now limited to vllm/entrypoints/pooling/scoring/api_router.py.

noooop · 2026-09-15T01:35:03Z

/ci run

github-actions · 2026-09-15T01:35:58Z

❌ This PR is 416 commits behind upstream main. Your branch must contain every commit currently on upstream main. No new CI build was started. Merge or rebase onto the latest main, then rerun /ci run. To test this branch at your own risk, use /ci run --allow-stale.

noooop · 2026-09-15T01:57:32Z

/ci run

github-actions · 2026-09-15T01:57:54Z

✅ Triggered Buildkite CI #88980 for commit f724c0d02971.

Signed-off-by: Miguel Garcia <miguelgarciaroman8@gmail.com>

migarci2 requested review from AndreasKaratzas, DarkLight1337, NickLucche, aarnphm, njhill and robertgshaw2-redhat as code owners September 6, 2026 18:30

claude Bot reviewed Sep 6, 2026

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mergify Bot added frontend bug Something isn't working labels Sep 6, 2026

taneem-ibrahim suggested changes Sep 7, 2026

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fix: avoid nested rerank cancellation handlers

00c1377

Remove redundant cancellation decorators from the v1 and v2 rerank aliases so the shared request has one disconnect listener. Assisted-by: AI coding assistant Signed-off-by: Miguel Garcia <miguelgarciaroman8@gmail.com>

migarci2 changed the title ~~[Bugfix] Clean up nested cancellation handlers~~ [Bugfix] Avoid nested rerank cancellation handlers Sep 7, 2026

migarci2 force-pushed the fix/rerank-cancellation branch from c284200 to 00c1377 Compare September 7, 2026 16:45

migarci2 requested a review from noooop as a code owner September 7, 2026 16:45

noooop reviewed Sep 8, 2026

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noooop approved these changes Sep 8, 2026

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git-jxj mentioned this pull request Sep 8, 2026

[Bugfix][Frontend] Clean up child tasks when request wrappers are cancelled #55790

Open

shaohuaxi mentioned this pull request Sep 12, 2026

[Bugfix][Pooling] Release cached queries when Flash scoring is cancelled #56617

Open

taneem-ibrahim suggested changes Sep 14, 2026

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test: drop extra scoring api_router test per review

c92bd92

Signed-off-by: Miguel Garcia <miguelgarciaroman8@gmail.com>

taneem-ibrahim approved these changes Sep 14, 2026

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noooop approved these changes Sep 15, 2026

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noooop added the verified Run pre-commit for new contributors without triggering other tests label Sep 15, 2026

noooop enabled auto-merge (squash) September 15, 2026 01:34

github-actions Bot added the ready ONLY add when PR is ready to merge/full CI is needed label Sep 15, 2026

Merge branch 'main' into fix/rerank-cancellation

f724c0d

noooop merged commit a72c046 into vllm-project:main Sep 15, 2026
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ItsRoy69 pushed a commit to ItsRoy69/vllm that referenced this pull request Sep 15, 2026

[Bugfix] Avoid nested rerank cancellation handlers (vllm-project#55602)

defedd6

Signed-off-by: Miguel Garcia <miguelgarciaroman8@gmail.com>

taneem-ibrahim mentioned this pull request Sep 15, 2026

[Bugfix] Avoid nested score cancellation handlers for /v1/score alias #57024

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