CVE-2026-89520

A flaw was found in the Linux kernel's core scheduling component. A race condition can occur when core scheduling flips complete during task selection, leading to incorrect lock handling. This can result in a resource leak and system instability, potentially causing a denial of service.

A flaw of MODERATE impact was found in the Linux kernel's core scheduling subsystem, affecting the kernel packages in Red Hat Enterprise Linux 9 and 10 and the RHEL CoreOS 9 based OpenShift Container Platform 4 releases. Core scheduling's pick_next_task() operates on all sibling runqueues (rqs) under a single acquisition of the shared core-wide lock, but a ->pick_task() implementation that releases the rq lock leaves every sibling lock momentarily free. This lets __sched_core_flip(false) complete mid-selection and rebind rq_lockp() underneath the in-progress selection. The selection then resumes on the split locks, touching sibling runqueue state it no longer protects, and __schedule() finally releases a lock that was never taken while leaking the lock that was. An unprivileged local user who triggers this race condition could cause a resource leak and system instability, potentially resulting in a denial of service; the race requires core scheduling to be in use, as the vulnerable window occurs during core-scheduling flip operations, which are rare cookie-lifetime events. Red Hat Enterprise Linux 6, 7, and 8 are not affected because the vulnerable code is not present in those kernels, and the RHEL CoreOS 8 based OpenShift Container Platform 4.12 is not affected for the same reason. For the affected products, the fix is currently deferred because this issue was assessed as MODERATE impact with a Red Hat CVSS 3.1 score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H), below the threshold at which fixes are prioritized; the residual risk is a local denial of service. This Red Hat severity rating is lower than the upstream CVSS 3.1 score of 7.8 because Red Hat assessed the impact of this flaw as affecting availability only, with no impact to confidentiality or integrity.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.