Tencent Architect

Oct 15, 2026 · Backend Development

Hunting a systemd Event Loop Bug: From vmcore to Upstream Fix

TencentOS Server 4 team debugs a boot hang caused by a systemd sd-event loop defect where pending tasks were ignored, leading to infinite epoll_wait; they traced it to a ratelimit expiry callback introduced in v250, built a reproducible PoC, and upstreamed a fix using an explicit state flag.