CVE-2026-64250
Received Received - Intake

RCU Deadlock in Linux Kernel LoongArch CPU Handling

Publication date: 2026-07-24

Last updated on: 2026-07-24

Assigner: kernel.org

Description
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.

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Meta Information

Published
2026-07-24
Last Modified
2026-07-24
Generated
2026-07-24
AI Q&A
2026-07-24
EPSS Evaluated
N/A
NVD
CVE-2026-64250
EUVD
EUVD-2026-48659

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability affects the Linux kernel on LoongArch systems. It involves a failure to properly report a CPU as offline to the RCU (Read-Copy-Update) mechanism during shutdown or reboot. When smp_send_stop() parks secondary CPUs, the scheduler marks them offline but does not inform RCU. This causes RCU to wait indefinitely for a quiescent state from these parked CPUs, leading to system hangs during reboot or shutdown if irq_work_sync() is called afterward.

Detection Guidance

This vulnerability is specific to the Linux kernel's LoongArch architecture and involves RCU (Read-Copy-Update) grace period stalls. Detection requires kernel logs showing RCU stalls or hangs during reboot/shutdown. Check for messages like 'Offline CPU blocking current GP' in dmesg or system logs after a reboot attempt.

Impact Analysis

This vulnerability can cause your Linux system to hang during reboot or shutdown. If the system attempts to synchronize RCU after stopping CPUs, it will wait forever for parked CPUs to respond, resulting in a complete system freeze. This disrupts normal operations and requires a hard reset to recover.

Compliance Impact

This vulnerability could potentially impact compliance with standards requiring reliable system shutdown or reboot processes, such as those related to data integrity and availability. A system hang during shutdown due to this issue may violate requirements for timely data processing or secure state transitions.

Mitigation Strategies

Apply the kernel patch that resolves this issue by ensuring RCU is informed when CPUs are taken offline. Update to a patched Linux kernel version that includes the fix for LoongArch's stop_this_cpu() function. Monitor kernel updates from your distribution.

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