CVE-2026-89520

In the Linux kernel, the following vulnerability has been resolved:

sched/core: Make core-sched flips wait for in-flight selections

Core scheduling's pick next task() operates on all sibling rqs under one acquisition of the shared core-wide lock. A ->pick task() that releases the rq lock leaves every sibling lock momentarily free, letting sched core flip(false) complete mid-selection and rebind rq lockp() under it. The selection resumes on the split locks, touching sibling state it no longer protects, and schedule() finally releases a lock that was never taken while leaking the one that was.

Count in-flight core-wide selections in the leader's rq->core pick in flight and make sched core flip() wait for the count to drain. The count only changes under the shared lock, which the flip holds while sampling, so no other ordering is needed. The wait can repeat while selections overlap, but the flip backs off between samples and flips are rare cookie-lifetime events.

sched core cpu deactivate() moves the count to the new leader - a stale copy left behind would bias it forever if that CPU later returns as its own leader.