CVE-2026-64250

In the Linux kernel, the following vulnerability has been resolved:

LoongArch: Report dying CPU to RCU in stop_this_cpu()

This is a port of MIPS commit 9f3f3bdc6d9dac1 (MIPS: smp: report dying CPU to RCU in stop_this_cpu()). smp_send_stop() parks all secondary CPUs in stop_this_cpu(). And the function marks the CPU offline for the scheduler via set_cpu_online(false) but never informs RCU, so RCU keeps expecting a quiescent state from CPUs that are now spinning forever with interrupts disabled.

As long as nothing waits for an RCU grace period after smp_send_stop() this is harmless, which is why it went unnoticed. However, since commit 91840be8f710370 (irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT), irq_work_sync() calls synchronize_rcu() on architectures without an irq_work self-IPI, i.e. where arch_irq_work_has_interrupt() returns false. Any irq_work_sync() issued in the reboot/shutdown/halt path after smp_send_stop() then blocks on a grace period that can never complete, hanging the reboot:

WARNING: CPU: 0 PID: 15 at kernel/irq_work.c:144 irq_work_queue_on … rcu: INFO: rcu_sched detected stalls on CPUs/tasks: rcu: Offline CPU 1 blocking current GP. rcu: Offline CPU 2 blocking current GP. rcu: Offline CPU 3 blocking current GP.

This issue needs some hacks to reproduce, and it was not noticed on LoongArch because arch_irq_work_has_interrupt() usually returns true.

Call rcutree_report_cpu_dead() once interrupts are disabled, mirroring the generic CPU-hotplug offline path, so RCU stops waiting on the parked CPUs and grace periods can still complete. LoongArch shuts down all CPUs here without going through the CPU-hotplug mechanism, so this report is not otherwise issued.

Affected Software

References

• https://git.kernel.org/stable/c/0833b2b84c2fc1387f8165f0cbf6a02d67f647a5
• https://git.kernel.org/stable/c/1fa22de588a65880d6fe54c38c87fffe7d519f60
• https://git.kernel.org/stable/c/262dadc619e69ebeb97affd334cd1078a9704e98
• https://git.kernel.org/stable/c/90e254f18b8c224460082329dd5c42fd30995c2f
• https://git.kernel.org/stable/c/a0269e928728f970c782319fee53d92d4ea4e512
• https://git.kernel.org/stable/c/f2539c56c74691e7a88af6372ba2b48c06ed2fe4