UBUNTU-CVE-2026-68421: Medium severity ubuntu/linux-hwe-edge vulnerability
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 ENQLAST 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-azure-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17~24.04.1 - Upgrade
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ubuntu/linux-azure-fde-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1016.16~24.04.1 - Upgrade
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ubuntu/linux-gcp-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1014.14~24.04.1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-38.38~24.04.4 - Upgrade
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ubuntu/linux-nvidia-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1024.25~24.04.1 - Upgrade
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ubuntu/linux-oracle-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1013.13~24.04.1 - Upgrade
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ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-38.38 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 7.0.0-1008.9 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1015.15 - Upgrade
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ubuntu/linux-nvidia-bosto a version that resolves this vulnerability.Fixed in 7.0.0-2022.23 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1015.15 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1013.13 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
In put_prev_task_scx(), gate the missing-SCX_OPS_ENQ_LAST warning on sched_cpu_cookie_match(): suppress it when core scheduling forced the CPU idle due to a cookie mismatch, while retaining the warning when cookies match or core scheduling is disabled.
Event History
Frequently Asked Questions
Which environments are most likely to trigger the warning addressed by this fix?
Systems using sched_ext together with core scheduling can trigger it when an SMT sibling is forced idle because of a scheduling-cookie mismatch. That reschedule path bypasses pick_task_scx() and balance_one().
How does the fix distinguish a benign forced-idle event from a genuine scheduling issue?
It suppresses the warning when sched_cpu_cookie_match() indicates a cookie mismatch, which identifies core scheduling as the cause of the forced idle. The warning remains active when cookies match or when core scheduling is disabled, preserving detection of a genuine missing-ENQ_LAST drop.