Daan De Meyer
a77838a950
The only runtime trigger for registry cleanup is the BPF kprobe that fires on user namespace destruction; when it is missed (ring buffer overflow, kprobe missing, fdstore entry dropped), the dead namespace's registry entry survives and keeps its UID/GID ranges blocked until the manager restarts and its startup sweep runs. The allocation hot path checked whether a candidate range was already taken but never whether the namespace holding it was still alive, so a single dead namespace could permanently starve an allocation. This is most visible when a parent delegates its entire container UID window to a child that then dies: every subsequent allocation from the parent fails with NoDynamicRange even though the ranges are reclaimable. Add userns_registry_reap_if_dead(), which probes a registered namespace's liveness via the kernel namespace identifier recorded at allocation time and, if it is authoritatively dead, releases its registry entry — restoring any ranges it received via delegation to their ancestors. Call it from the allocation availability check for both transient registrations and delegated ranges, walking a chain of dead ancestors in the delegation case. This mirrors the existing inode-slot stale cleanup and makes allocation self-healing without waiting for a restart. The startup sweep grew the same load-probe-release logic, so route it through the new helper too; its errno return distinguishes alive, no-recorded-id, and unprobeable-environment cases so the sweep keeps its early-out when lookup by id isn't possible at all. Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>
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