When hermes-auto-update runs \hermes update\ from cron, the update
process lives INSIDE the gateway's own process tree. Waiting for that
gateway to exit is a circular wait:
gateway waits on all in-flight work units (#77184 don't-amputate)
-> cron agent session waits on the \hermes update\ process to exit
-> \hermes update\ waits on the gateway to exit [back to A]
The wedged-loop probe (#81642) cannot break it: the cron session posts
activity every ~180s (process-tool poll return), so it is 'actively
waiting forever' and never marked wedged. The gateway logs
'Restart deferred: waiting on 1 active work unit(s)' every 30s until the
1800s force-drain cap amputates its own updater's session — reported as
a 5+ minute hang with gateway_state.json stuck at draining +
restart_requested (v0.21.0, main @ 530aa7b10f).
Fix (the issue's recommended option 1): at both drain sites in
update_cmd.py — systemd (line ~9862) and the bare-process/launchd path
(line ~10203) — check \_is_pid_ancestor_of_current_process(pid)\ before
drain-waiting. When the target gateway IS an ancestor, use
\_request_gateway_self_restart\ (SIGUSR1, no exit-wait) and return: the
gateway's own restart flow completes normally once this process, and
therefore the cron work unit holding it, exits.
Both helpers already exist in hermes_cli/gateway.py (277-304) and
\_request_gateway_self_restart\ already refuses non-ancestor PIDs, so a
normal out-of-tree \hermes update\ keeps its full drain semantics
(including the #86684 cron floor) untouched.
Tests (tests/hermes_cli/test_update_cron_deadlock_guard.py, 6):
- own PID / parent PID are ancestors; 0 and negative are not
- self-restart refuses a non-ancestor PID [linux]
- ancestor path sends SIGUSR1 and NEVER calls _wait_for_pid_exit
(the deadlock witness — a wait there is the bug) [linux]
- non-ancestor path still drain-waits with the given budget [linux]
Existing graceful/sigusr1/restart tests pass unchanged (9 passed).
Fixes#100179
49a71c9727