---
id: "bug-1282"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "lib"
severity: "crash"
timestamp: "2026-06-30T04:17:08.329Z"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 3
files: ["src/lib/dataq.c:65 (dataq_deq holds q->lock across match cb) + src/lib/vtaskmgr.c:255 (vtask_eligible) + src/lib/netio.c:1001 (endpoint_is_task_blocked takes ep->lock) + src/lib/netio.c:672 (io_worker holds ep->lock across vtask_enq->dataq_enq)"]
tags: ["deadlock", "lock-order", "abba", "vtaskmgr", "dataq", "netio", "io_worker", "vdispatcher", "raft-drive-async", "async-io", "upstream", "async-fix", "md"]
related: ["bug-1281"]
fix_commits: ["25e741d"]
legacy: true
---

# bug-1282: ABBA lock-order deadlock under chaotic churn: io_worker (ep->lock then dataq_enq wants q->lock) vs…

## Description
ABBA lock-order deadlock under chaotic churn: io_worker (ep->lock then dataq_enq wants q->lock) vs vdispatcher dataq_deq (q->lock then vtask_eligible->endpoint_is_task_blocked wants ep->lock). Wedges io_worker -> controller stops accepting connections; in release the race corrupts -> SIGSEGV.

## Environment
_Not recorded (migrated from buglog.json)._

## Reproduction
_Not recorded (migrated from buglog.json)._

## Root cause
dataq_deq runs its match callback while holding q->lock, and the callback (vtask_eligible->endpoint_is_task_blocked) acquires ep->lock — inverting the ep->lock->q->lock order io_worker uses. Two-thread ABBA deadlock, deterministic under round-4 chaotic churn. Confirmed via gdb all-thread backtrace on two independently-wedged nodes.

## Fix
FIXED (commit 25e741d): promoted endpoint_t.busy from a 1-bit bitfield to _Atomic int; endpoint_block_tasks/endpoint_unblock_tasks/endpoint_is_task_blocked now lockless (release/acquire), removing the ep->lock acquire from the vtask-eligibility path that ran under q->lock. Verified: post-fix gdb soak has ZERO __lll_lock_wait threads + no endpoint_is_task_blocked in any lock path; controller_unit_test all green. Mirrors dispatch_inflight (bug-1197). NOTE: a SEPARATE release-only restart segfault (bug-1283) remains and still blocks 7.2.

## Verification
_Not recorded (migrated from buglog.json)._

## References
- Related: bug-1281