CVE-2025-21897 sched_ext: Fix pick_task_scx() picking non-queued tasks when it's called without balance()

In the Linux kernel, the following vulnerability has been resolved: schedext: Fix picktaskscx picking non-queued tasks when it's called without balance a6250aa251ea "schedext: Handle cases where picktaskscx is called without preceding balancescx" added a workaround to handle the cases where...

CVE-2025-21897

CVE-2025-21897: Linux kernel sched_ext vulnerability where pick_task_scx() could return non-queued tasks if balance() wasn’t called. The fix adds a workaround to emulate SCX_RQ_BAL_KEEP only when preceding balance_scx() is missing, and corrects the prior test that used @prev to decide if a task w...