sched_ext: Fix stale direct dispatch state in ddsp_dsq_id

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Summary

CVECVE-2026-31733
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-01 15:16:35 UTC
Updated2026-05-01 15:24:14 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix stale direct dispatch state in ddsp_dsq_id @p->scx.ddsp_dsq_id can be left set (non-SCX_DSQ_INVALID) triggering a spurious warning in mark_direct_dispatch() when the next wakeup's ops.select_cpu() calls scx_bpf_dsq_insert(), such as: WARNING: kernel/sched/ext.c:1273 at scx_dsq_insert_commit+0xcd/0x140 The root cause is that ddsp_dsq_id was only cleared in dispatch_enqueue(), which is not reached in all paths that consume or cancel a direct dispatch verdict. Fix it by clearing it at the right places: - direct_dispatch(): cache the direct dispatch state in local variables and clear it before dispatch_enqueue() on the synchronous path. For the deferred path, the direct dispatch state must remain set until process_ddsp_deferred_locals() consumes them. - process_ddsp_deferred_locals(): cache the dispatch state in local variables and clear it before calling dispatch_to_local_dsq(), which may migrate the task to another rq. - do_enqueue_task(): clear the dispatch state on the enqueue path (local/global/bypass fallbacks), where the direct dispatch verdict is ignored. - dequeue_task_scx(): clear the dispatch state after dispatch_dequeue() to handle both the deferred dispatch cancellation and the holding_cpu race, covering all cases where a pending direct dispatch is cancelled. - scx_disable_task(): clear the direct dispatch state when transitioning a task out of the current scheduler. Waking tasks may have had the direct dispatch state set by the outgoing scheduler's ops.select_cpu() and then been queued on a wake_list via ttwu_queue_wakelist(), when SCX_OPS_ALLOW_QUEUED_WAKEUP is set. Such tasks are not on the runqueue and are not iterated by scx_bypass(), so their direct dispatch state won't be cleared. Without this clear, any subsequent SCX scheduler that tries to direct dispatch the task will trigger the WARN_ON_ONCE() in mark_direct_dispatch().

Risk And Classification

EPSS: 0.000180000 probability, percentile 0.046430000 (date 2026-05-05)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 5b26f7b920f76b2b9cc398c252a9e35e44bf5bb9 ca685511f7afd42cdcbb0feea42e5d332d384251 git Not specified
CNA Linux Linux affected 5b26f7b920f76b2b9cc398c252a9e35e44bf5bb9 5e7b2cc8fae9ec2a5bc53311191d2faaff75a4b5 git Not specified
CNA Linux Linux affected 5b26f7b920f76b2b9cc398c252a9e35e44bf5bb9 7ea601daa0153e19cd1c6e6b300348c70c05fe77 git Not specified
CNA Linux Linux affected 5b26f7b920f76b2b9cc398c252a9e35e44bf5bb9 7e0ffb72de8aa3b25989c2d980e81b829c577010 git Not specified
CNA Linux Linux affected 6.12 Not specified
CNA Linux Linux unaffected 6.12 semver Not specified
CNA Linux Linux unaffected 6.12.82 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.22 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.12 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/7ea601daa0153e19cd1c6e6b300348c70c05fe77 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7e0ffb72de8aa3b25989c2d980e81b829c577010 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5e7b2cc8fae9ec2a5bc53311191d2faaff75a4b5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ca685511f7afd42cdcbb0feea42e5d332d384251 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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