CVE-2026-89519: In the Linux kernel, the following vulnerability has been resolved: sched_ext: Replace SCX_RQ_BAL_KEEP with a dispatch

A vulnerability in the Linux kernel's sched_ext (scheduler extension) was fixed by replacing SCX_RQ_BAL_KEEP, a flag that told the task scheduler to keep running the previous task, with an explicit return value that travels with the dispatch (the decision to assign a task to a processor). The old flag-based approach failed when core scheduling (using multiple logical processors on the same core) interleaved operations, allowing stale decisions to keep tasks that had already been removed from the queue.