Linux Kernel Task Requeuing Vulnerability on Excluded CPUs

A vulnerability in the Linux kernel's scheduling component can lead to improper task management on large machines. The issue arises when a task that is being descheduled is requeued on a CPU that should not be processing it. This problem was observed early in the boot process on a distribution kernel, but is likely present in the mainline kernel as well. The vulnerability stems from a commit that optimized task waking procedures without ensuring that tasks are allowed to run on specific CPUs. As a result, tasks can be incorrectly queued, triggering warnings and potentially disrupting normal operations.

Impact

The vulnerability can cause scheduling warnings and disrupt the proper migration of tasks between CPUs, particularly affecting workqueue rescue threads that handle per-cpu work.

Reproduction

The vulnerability can be reproduced on a large machine by allowing the udev process to wake up tasks on CPUs that are not supposed to handle them. This can be done by triggering the conditions that cause the workqueue rescue thread to run, such as reaching the MAYDAY_INITIAL_TIMEOUT or MAYDAY_INTERVAL on a large machine.

Remediation

No specific remediation is mentioned, but the issue has been addressed in the Linux kernel.