In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix CPU hotplug hang when a dying CPU's tasks sit in the BPF… (CVE-2026-99085)

The Linux kernel sched_ext scheduler had a flaw where CPU hotplug hangs occurred if a dying CPU's tasks were managed by the BPF scheduler. The hotplug thread waits for the CPU's runqueue to empty, but tasks held by the BPF scheduler remained counted on the runqueue without being pulled off, causing the hotplug thread to hang or stall indefinitely. The fix involves re-enqueuing tasks on the local dequeue when the runqueue goes offline and ensuring dispatch operations continue until the runqueue is fully offline, allowing the hotplug thread to complete properly.

This vulnerability could cause CPU hotplug operations to hang, potentially leading to system stalls or delays during CPU offline procedures. Systems using the sched_ext scheduler with BPF-managed tasks on CPUs being taken offline may experience hangs or stalls, impacting system stability and availability during CPU hotplug events.

A fix has been implemented in the Linux kernel to address this issue. Users should update to a kernel version that includes this fix to prevent CPU hotplug hangs related to the sched_ext scheduler and BPF-managed tasks. Patch status is not explicitly stated in the provided data; users should consult the official Linux kernel advisories or release notes for the specific fixed version and apply the update accordingly.