In the Linux kernel, enabling function tracing or kprobes while a CPU enters an ACPI Low Power Idle (LPI) state causes the acpi_idle_lpi_enter function to be called after RCU has been disabled. Ftrace’s function_trace_call then expects RCU monitoring and emits a warning, producing an RCU splat. This warning indicates that trace instrumentation is incorrectly active when RCU is not on, which can lead to kernel instability or repeated logging without directly exposing sensitive data or allowing code execution. The bug corresponds to CWE‑820, reflecting a design flaw that allows a tracing facility to operate in an improper state.

All Linux kernel builds that use the ACPI processor_idle implementation and do not yet contain the __cpuidle annotation for the LPI entry functions, regardless of vendor. The problem exists in kernels prior to the patch that adds the annotation and moves to the .cpuidle.text section; it is not tied to a specific vendor version but applies to any affected release of the Linux kernel.

The EPSS score is <1%, indicating a very low likelihood of exploitation, and the vulnerability is not listed in CISA’s KEV catalog. The CVSS score is 5.5, which indicates moderate impact. Because exploitation requires privileged kernel tracing or kprobe configuration, the typical risk to ordinary users is low. Nevertheless, the warning can affect system stability and may trigger unwanted alerts. Applying the kernel update that annotates acpi_idle_lpi_enter and related functions with __cpuidle removes the ftrace path and eliminates the RCU warnings, thereby mitigating the risk.