Cancel misses a batch mid-promotion, letting a cancelled request reach speculation

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@burgulvedant is already working on this.

Since Oct 31, 2026.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
go
Domain
distributed-systems

Research direction

Start by tracing dependency analysis around claimRequestsForBatch and the creating-to-created transition, then follow cancellation through markCancelling, findBatches, and cancelRequest. Check how speculation admits created batches and review the constraints from #817. Done means a cancelled request cannot reach speculation while created batches remain dependency-eligible; run the relevant tests for these transitions.

Written by the indexing model from the issue text.

Description

bug

Problem

A request cancelled in the window between dependency analysis claiming it (validated → batched) and promoting its batch out of creating reaches speculation anyway. The result is a live batch carrying a request the user cancelled; it will build, and it can merge.

Interleaving

dependency analysis:  request validated → batched     (claimRequestsForBatch)
cancel:               request batched → cancelling    (markCancelling)
cancel:               findBatches sees only a creating batch — not cancellable
cancel:               request cancelling → cancelled  (no applicable batch → cancelRequest)
dependency analysis:  batch creating → created        (batch-only compare-and-swap)
dependency analysis:  publish to speculate

Why the existing guards miss it

  • The halted-request check in dependency analysis runs before the claim.
  • The claim's re-read and version check reject a cancel that lands before or during the claim, but this window opens after the claim succeeds.
  • creating is not cancellable, so cancel's batch loop matches nothing and falls through to cancelRequest.
  • Neither speculate's admission of created batches nor conclude checks for halted requests.

Found in review of #590. As of 6c050082 the code paths above are unchanged.

Constraint

From #817: a batch abandoned in creating must stay unreachable, and created must remain dependency-eligible.

Dominant language
Go
Stars
247
Forks
16
Avg merge
2d 1h
Merged PRs (30d)
125

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