Executive brief
A vulnerability in the Linux kernel's Sleepable Read-Copy-Update (SRCU) mechanism can cause system hangs, particularly on s390 architectures. The issue occurs when the system attempts to process tasks on processor cores that are not currently active or do not exist. This could lead to a denial-of-service condition where the operating system becomes unresponsive.
Technical details
A race condition exists in the Linux kernel's Tree SRCU implementation during the transition from a single-CPU (CPU-0) state to an all-CPUs state. The `srcu_struct` may attempt to invoke callbacks on CPUs that are not yet online or are not present in the `cpu_possible_mask`. This behavior causes kernel hangs, specifically observed on s390 architectures which cannot handle workqueue scheduling on such CPUs. The fix involves checking if a CPU has been fully online using `rcu_cpu_beenfullyonline()` before queueing handlers and redirecting early callbacks to the boot CPU. Affected versions include early 7.x releases, with patches available in stable branches.
Affected products
- Linux Linux 7.0, 7.1
Timeline
- 2026-05-11: other: Patch authored
- 2026-07-24: disclosed: CVE published