sched_ext: Fix starvation of scx_enable() under fair-class saturation

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Summary

CVECVE-2026-43392
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-08 15:16:50 UTC
Updated2026-05-12 14:10:27 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix starvation of scx_enable() under fair-class saturation During scx_enable(), the READY -> ENABLED task switching loop changes the calling thread's sched_class from fair to ext. Since fair has higher priority than ext, saturating fair-class workloads can indefinitely starve the enable thread, hanging the system. This was introduced when the enable path switched from preempt_disable() to scx_bypass() which doesn't protect against fair-class starvation. Note that the original preempt_disable() protection wasn't complete either - in partial switch modes, the calling thread could still be starved after preempt_enable() as it may have been switched to ext class. Fix it by offloading the enable body to a dedicated system-wide RT (SCHED_FIFO) kthread which cannot be starved by either fair or ext class tasks. scx_enable() lazily creates the kthread on first use and passes the ops pointer through a struct scx_enable_cmd containing the kthread_work, then synchronously waits for completion. The workfn runs on a different kthread from sch->helper (which runs disable_work), so it can safely flush disable_work on the error path without deadlock.

Risk And Classification

EPSS: 0.000180000 probability, percentile 0.047270000 (date 2026-05-12)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 8c2090c504e998c8f34ec870bae71dafcc96a6e0 e0b14bf06393be137d3efb6a3b7cd5b4b9810a6b git Not specified
CNA Linux Linux affected 8c2090c504e998c8f34ec870bae71dafcc96a6e0 c44198f25fdfecc0ec0fe366bf8a47fe17d8e229 git Not specified
CNA Linux Linux affected 8c2090c504e998c8f34ec870bae71dafcc96a6e0 05ab9ec5dc24f234e0a2fecf3e6ff937c68f7d81 git Not specified
CNA Linux Linux affected 8c2090c504e998c8f34ec870bae71dafcc96a6e0 b06ccbabe2506fd70b9167a644978b049150224a git Not specified
CNA Linux Linux affected 6.12 Not specified
CNA Linux Linux unaffected 6.12 semver Not specified
CNA Linux Linux unaffected 6.12.78 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.20 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.9 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/05ab9ec5dc24f234e0a2fecf3e6ff937c68f7d81 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c44198f25fdfecc0ec0fe366bf8a47fe17d8e229 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b06ccbabe2506fd70b9167a644978b049150224a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e0b14bf06393be137d3efb6a3b7cd5b4b9810a6b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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