Linux Kernel RCU Preemption Warning Lockdep Issue

A lockdep warning related to the RCU (Read-Copy-Update) mechanism has been addressed in the Linux kernel. The issue arose in a preemptible kernel when running the rcutorture tool with a non-zero fqs_duration parameter. This combination triggered a warning because the rcu_force_quiescent_state() function improperly used __this_cpu_read() in preemptible code, instead of the correct raw_cpu_read(). The vulnerability is present in Linux kernel versions 6.0.0-rc1-yoctodev-standard and prior.

Impact

The vulnerability could lead to improper handling of CPU preemption in RCU operations, potentially causing synchronization issues or performance degradation.

Reproduction

To reproduce this issue, run a Linux kernel version that is preemptible (with CONFIG_PREEMPTION=y) and execute the rcutorture tool with a non-zero fqs_duration parameter. This will generate a lockdep warning about the improper use of __this_cpu_read() in preemptible code.

Remediation

Users can upgrade to the latest stable version of the Linux kernel, where this issue has been fixed. Instructions for downloading the latest version can be found on the official Linux kernel website.