sched_ext: Fix CPU hotplug hang when a dying CPU's tasks sit in the BPF scheduler

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Summary

CVECVE-2026-99085
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-23 13:17:32 UTC
Updated2026-10-23 13:17:32 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix CPU hotplug hang when a dying CPU's tasks sit in the BPF scheduler A CPU going down has to empty its own rq. Its hotplug thread waits in sched_cpu_wait_empty() until nothing else is left, and the only thing that wakes it is balance_push(), which runs from __schedule() on the dying CPU and pushes off the migratable tasks the CPU picks. sched_ext breaks this. A task sitting on a user DSQ or held by the BPF scheduler is still counted on its rq, but an inactive CPU no longer calls ops.dispatch() and can't pull the task back. The dying CPU goes idle with the task still counted, and one of two things happens: - Another CPU consumes the task. The rq empties without a __schedule() on the dying CPU, so the hotplug thread is never woken and cpu_down() hangs holding cpu_hotplug_lock. - The task is affine only to the dying CPU. Nothing can move it, and the offline stalls until the watchdog ejects the BPF scheduler. When the rq goes offline, re-enqueue every task on it that isn't already on the local DSQ. An enqueue on an offline rq lands on the local DSQ, so the dying CPU itself picks the tasks and balance_push() pushes them off, the same as for the other sched classes. From then on no sched_ext path on another CPU can pull a task off the rq. ops.dispatch() currently stops as soon as the CPU goes inactive, and CPU hotplug then waits for an RCU grace period before taking the rq offline. A BPF-held task affine only to the dying CPU and preempted inside an RCU read-side critical section would block that grace period, and the rq would never go offline. Test SCX_RQ_ONLINE directly so that ops.dispatch() keeps running until the rq goes offline. Only the dying CPU's own hotplug thread clears the flag during teardown, and task_can_run_on_remote_rq() still keeps other rqs' tasks off the CPU.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected f0e1a0643a59bf1f922fa209cec86a170b784f3f f79cd7a2df3768323fbfb9b0f96adff08fb7eb4c git Not specified
CNA Linux Linux affected f0e1a0643a59bf1f922fa209cec86a170b784f3f 638ee6bca19750934ea13f9c325f46fd8ae60064 git Not specified
CNA Linux Linux affected f0e1a0643a59bf1f922fa209cec86a170b784f3f 173ff9d03ec6373c3158b6e630af33a9b36fd216 git Not specified
CNA Linux Linux affected f0e1a0643a59bf1f922fa209cec86a170b784f3f d35a535d3e3e71f92a051d94e415f43612c4edfc git Not specified
CNA Linux Linux affected 6.12 Not specified
CNA Linux Linux unaffected 6.12 semver Not specified
CNA Linux Linux unaffected 6.12.114 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.58 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.12 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/638ee6bca19750934ea13f9c325f46fd8ae60064 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f79cd7a2df3768323fbfb9b0f96adff08fb7eb4c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/173ff9d03ec6373c3158b6e630af33a9b36fd216 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d35a535d3e3e71f92a051d94e415f43612c4edfc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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