Bug 2513236 (CVE-2026-68421)

Summary: CVE-2026-68421 kernel: sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's `sched_ext` component. The `put_prev_task_scx()` function incorrectly issues a warning when a runnable task transitions to an idle state due to core scheduling. This occurs because the core scheduling mechanism bypasses certain checks, leading to a misleading warning.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-10 12:26:22 UTC 
In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx()

put_prev_task_scx() warns when a runnable task drops to a lower sched_class
without SCX_OPS_ENQ_LAST, on the assumption that balance_one() would have
kept it running. Core scheduling breaks that: a forced-idle SMT sibling
reschedules through the core_pick fast path in pick_next_task(), which skips
pick_task_scx() and thus balance_one(), so a runnable task can drop to idle
with ENQ_LAST unset.

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