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openstack-caracal-dc-dc / docs / changelog-20260710-carve-gua-hang-fix.md
@JANeumatrix JANeumatrix 3 hours ago 2 KB DOCFIX-181: fix carve_gua subnet-enumeration hang (gauntlet was stalling)
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Changelog 2026-07-10 -- DOCFIX-181: carve_gua subnet-enumeration hang + harness watchdog

Context. After the Stage-1 commit, the full scripts/run-tests-all.sh gauntlet was seen to HANG on tests/dc-dc-prefixes-import/. Investigated per operator request ("check into this now so it's not a problem later"). Root cause is a real bug in the target script, not an environment quirk -- and the harness's own claimed "40/40 PASS" was never actually reached (it was hanging).

Root cause

netbox/dc-dc-prefixes-import.py::carve_gua() built list(dc_gua_prefix.subnets(new_prefix=64)) -- materializing EVERY /64 in the GUA prefix, then returning only the first. D-101's own GUA example is a /40 (2602:f3e2:1000::/40), which has 2**(64-40) = 16,777,216 /64 subnets, so the list() allocates ~16.7M IPv6Network objects -> effective hang / OOM. This is NOT test-only: a real import run with a realistic GUA prefix would hang identically. (carve_ula is safe -- it carves /48->/56->/64, bounded at 256.)

Diagnosed with faulthandler.dump_traceback_later, which pointed straight at carve_gua line 306 inside ipaddress.subnets().

Fix

  • netbox/dc-dc-prefixes-import.py::carve_gua -- take the first /64 LAZILY with next(dc_gua_prefix.subnets(new_prefix=64)) (O(1)) instead of list(...)[0]. Same result, no enumeration.
  • tests/dc-dc-prefixes-import/test_logic.py -- added a faulthandler.dump_traceback_later(30, exit=True) watchdog at import time, so any FUTURE blocking regression in this Python test self-aborts after 30s with a stack trace (non-zero exit) rather than hanging the whole gauntlet silently.

Verification

  • bash tests/dc-dc-prefixes-import/run-tests.sh -> ALL PASS (40 checks) in ~0.05s (previously: hung indefinitely, never completing).
  • bash scripts/repo-lint.sh -> 0 fail.
  • Full scripts/run-tests-all.sh gauntlet now runs to completion.

Revert

  • git checkout netbox/dc-dc-prefixes-import.py tests/dc-dc-prefixes-import/test_logic.py to the pre-DOCFIX-181 revision, plus git rm docs/changelog-20260710-carve-gua-hang-fix.md. (Reverting reinstates the hang -- do not, without replacing the fix.)

Note

  • The pre-existing ledger claim of "dc-dc-prefixes-import 40/40" was optimistic: the end-to-end path had been hanging, so those checks never actually ran to a green count until this fix. The watchdog prevents that class of false-green (a hang read as "still running") from recurring.