CVE-2026-68421

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

schedext: Don't warn on core-sched forced idle in putprevtaskscx()

putprevtaskscx() warns when a runnable task drops to a lower schedclass without SCXOPSENQLAST, on the assumption that balanceone() would have kept it running. Core scheduling breaks that: a forced-idle SMT sibling reschedules through the corepick fast path in picknexttask(), which skips picktaskscx() and thus balanceone(), so a runnable task can drop to idle with ENQ_LAST unset.

Gate the warning on schedcpucookiematch(): a cookie mismatch means core scheduling forced the idle, while a match (or core scheduling off) still catches a genuine missing-ENQLAST drop.