[Bugfix][NIXL] Don't assert when a failed transfer is cleaned up twice - #54518
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aaron-seq
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aaron-seq
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The diagnosis holds up. done_recving is a set, so the duplicate is across successive get_finished calls rather than within one: the first drains a queued copy and pops the metadata, a later one drains the second handle's copy and finds nothing. _handle_failed_transfer reading with .get() while the cleanup asserted was a real contradiction, and turning an engine kill into a skipped iteration is the right call.
One thing the fix leaves open, on the test line below: the id is still returned in done_recving on the second pass, so the scheduler is told the same request finished receiving twice. Worth confirming that is tolerated rather than just untested.
| with patch.object(worker.nixl_wrapper, "check_xfer_state", return_value="ERR"): | ||
| _, done_recving = connector.get_finished(finished_req_ids=set()) | ||
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| assert request_id in done_recving |
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This assert is the interesting one. It pins that the same id is reported finished to the scheduler on both polls, which is the half of the bug the fix does not address: continue skips the metadata work, but the id is still in done_recving at the return. Is the scheduler idempotent about a request landing in finished_recving twice? If it is, worth saying so here, since the test currently reads as asserting the duplicate is fine without stating why.
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NickLucche
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Hey @jyizheng , thanks a lot for the work!
I addressed a few nits, hope it's ok
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✅ @jyizheng, CI is now available for this PR.
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/ci run |
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✅ Triggered Buildkite CI #86909 for commit |
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Thanks @jyizheng @NickLucche. I feel like this might be a better root-cause fix which maintains the invariant (commit on top of this branch): njhill@1c3aeaf, WDYT? |
Yes. It is okay. |
Thanks @njhill — yours is better, let's go with it. Fixing it where the I'll take your commit onto the branch. |
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Repository UI Review profile: CHILL Plan: Team Run ID: 📒 Files selected for processing (2)
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Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review. 📝 SummarySummary by CodeRabbit
WalkthroughThe NIXL connector reports a multi-handle receive failure once across separate polls. Later failures release remaining handles without duplicate reporting. A regression test covers this two-poll sequence. ChangesNIXL failure handling
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to NIXL receive failures are now reported once per request when transfer handles fail across separate polls, preventing duplicate cleanup assertions while retaining cleanup of remaining handles. No concrete merge-blocking risk remains in the supplied evidence. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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/ci run |
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✅ Triggered Buildkite CI #87305 for commit |
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A request's KV is pulled with one transfer handle per remote rank. When a peer goes away the handles do not all fail in the same poll: one errors while another is still PROC. Each failure queues the request id on _failed_recv_reqs, so get_finished() sees the same id once per handle. That repeat hits two engine-wide asserts. The cleanup loop pops the request's metadata with a default and then asserts it is not None, so the second pass raises out of worker_busy_loop. Dropping that assert alone is not enough: the id is still returned in done_recving, and the scheduler asserts in _update_from_kv_xfer_finished on a finished recv for a request it has already moved out of WAITING_FOR_REMOTE_KVS to recompute locally. Tolerate the missing metadata and drop the repeat from done_recving, so a failed transfer costs its own request rather than the engine and every request batched with it. Observed on a 10-prefill/3-decode disaggregated deployment when three prefill nodes lost their NICs. Signed-off-by: Yizheng Jiao <jyizheng@gmail.com>
Signed-off-by: NickLucche <nicolo.lucchesi@mistral.ai>
A request's transfer has one handle per remote rank, and they do not all fail in the same poll: each failure re-queued the id on _failed_recv_reqs and the last surviving handle re-reported it from _pop_done_transfers. _recving_metadata presence already witnesses "not yet reported" (set in start_load_kv, popped only by get_finished), so key both producers on it: _handle_failed_transfer only invalidates blocks and queues the id while metadata remains, and _pop_done_transfers only reports completion while metadata remains. This restores the get_finished metadata assert as a genuine invariant instead of tolerating repeats there. Co-authored-by: Kimi Code Signed-off-by: Nick Hill <nickhill123@gmail.com>
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Note GitHub couldn't provide a complete incremental comparison for this pull request, so CodeRabbit is performing a full review instead. This review may take a little longer. |
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/ci run |
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✅ Triggered Buildkite CI #87323 for commit |
vllm-project#54518) Signed-off-by: Yizheng Jiao <jyizheng@gmail.com> Signed-off-by: NickLucche <nicolo.lucchesi@mistral.ai> Signed-off-by: Nick Hill <nickhill123@gmail.com> Co-authored-by: NickLucche <nicolo.lucchesi@mistral.ai> Co-authored-by: Nick Hill <nickhill123@gmail.com> Signed-off-by: Jyotirmoy Roy <jyotirmoyroy649@gmail.com>
4 participants
Purpose
A request's KV is pulled with one transfer handle per remote rank. When a peer goes away the handles do not all fail in the same poll: one errors while another is still
PROC. Each failure queues the request id on_failed_recv_reqs, soget_finished()sees the same id once per handle.That repeat hits two engine-wide asserts:
base_worker.pypops the request's metadata with a default and then asserts it is not None, so the second pass raises out ofworker_busy_loop.done_recving, andScheduler._update_from_kv_xfer_finishedasserts on a finished recv for a request it has already moved out ofWAITING_FOR_REMOTE_KVSto recompute locally.This tolerates the missing metadata and drops the repeat from
done_recving, so a failed transfer costs its own request rather than the engine and every request batched with it._handle_failed_transferalready reads the metadata with.get()and leaves cleanup toget_finished.Observed on a 10-prefill/3-decode disaggregated deployment when three prefill nodes lost their NICs.
Test Plan
test_handles_failing_in_separate_polls_do_not_kill_the_enginegives a request a second handle and fails them in two polls, asserting the second poll neither raises nor re-reports the request.Test Result
Both asserts reproduce against the unpatched worker and are gone after the change.