[Bugfix][KVConnector] Don't crash scheduler on stale KV transfer completions - #53746
[Bugfix][KVConnector] Don't crash scheduler on stale KV transfer completions#53746linhongyu510 wants to merge 1 commit into
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MultiConnector deduplicates async saves across sub-connectors but does a bare union for async loads (finished_recving). In a P/D setup where the decode engine runs a second connector doing async loads, a request can finish via the faster load path and be removed from the scheduler while a slower connector's load is still in flight. When that late completion is finally reported, the scheduler hit `assert req_id in self.requests` in _update_from_kv_xfer_finished, killing the engine (EngineDeadError). A late/stale load- or send-completion report for an already-removed request is state-wise harmless. Replace the asserts with a warn-and-skip so a stale report no longer takes down the engine. Fixes vllm-project#53049 Signed-off-by: linhongyu510 <linhongyu510@users.noreply.github.com>
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| logger.debug("Finished recving KV transfer for request %s", req_id) | ||
| assert req_id in self.requests | ||
| req = self.requests[req_id] | ||
| req = self.requests.get(req_id) |
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Please add e2e test results on some large model.
| # connectors load the same request and the faster one already | ||
| # completed it). This is state-wise harmless, so warn and skip | ||
| # instead of crashing the engine with an assertion error. | ||
| logger.warning( |
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can we have one warning printed instead of printing it every time?
| logger.debug("Finished recving KV transfer for request %s", req_id) | ||
| assert req_id in self.requests | ||
| req = self.requests[req_id] | ||
| req = self.requests.get(req_id) |
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PR #53049 is not yet merged. Why this is added as a separate PR and not as a part of the main PR?
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Purpose
Fixes #53049.
MultiConnectordeduplicates async saves across sub-connectors (via_extra_async_saves) but performs a bare union for async loads (finished_recving). In a P/D disaggregation setup where the decode engine also runs a second connector doing async loads (e.g. NIXL pull + LMCache MP), a request can complete via the faster load path and be removed from the scheduler while the slower load is still in flight. When that late completion is finally reported, the scheduler hits:which raises
EngineDeadErrorand takes the decode engine down until a manual restart.The same asymmetry applies to
finished_sending.This PR takes the defense-in-depth direction (#3 in the issue's suggested fixes): a late/stale load- or send-completion report for a request that is no longer tracked by the scheduler is state-wise harmless, so we replace the two
assert req_id in self.requestschecks in_update_from_kv_xfer_finishedwith a warn-and-skip. This prevents the crash reported in the issue.Note: the deeper connector-level dedup / memory-safety work (directions #1 and #2 — mirroring
_extra_async_savesfor loads inMultiConnector, and pinning blocks for in-flight NIXL pulls) is left for a follow-up, as it requires the NIXL/LMCache topology to validate. This change is a minimal, safe guard against the fatal engine crash.Test Plan
Added two regression tests in
tests/v1/core/test_scheduler.py:test_stale_finished_recving_is_ignoredtest_stale_finished_sending_is_ignoredBoth feed a
KVConnectorOutputreporting a completion for areq_idthe scheduler is not tracking, and assert thatupdate_from_outputdoes not raise.pytest tests/v1/core/test_scheduler.py -k "stale_finished" -qTest Result
The new tests pass; without the fix they fail with
AssertionErrorinside_update_from_kv_xfer_finished, reproducing the reported crash. Existing KV-connector scheduler tests are unaffected.