Executive brief
The Linux kernel's memory reclamation routine (shrink_lruvec) can cause RCU-tasks stalls when running on preemptible kernels, preventing proper system responsiveness monitoring. This manifests as watchdog warnings indicating kernel tasks are not yielding control properly, which could delay system shutdown, emergency memory freeing, or other critical kernel operations during memory pressure.
Technical details
The vulnerability is a missing RCU (Read-Copy-Update) quiescent state report in the shrink_lruvec() function's scan loop in mm/vmscan.c. The function calls cond_resched(), which is a no-op on CONFIG_PREEMPTION kernels and does not constitute a Tasks-RCU quiescent state. Tasks performing direct memory reclaim can thus block indefinitely without reporting quiescence, causing RCU-tasks stalls detected by kernel watchdogs. The fix upgrades the call to cond_resched_tasks_rcu_qs(), which reports a quiescent state even when preemption is disabled. No authentication or network access is required; this affects any system performing memory reclaim under memory pressure on affected kernel versions.
Affected products
- Linux Linux kernel multiple versions from 2.6.11 through 6.x (pre-patch)
Timeline
- 2026-09-11: disclosed
- 2026-08-10: patched: Fix committed upstream by Breno Leitao