sched_ext: Fix rq->core_pick corruption under core scheduling

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89517
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:34 UTC
Updated2026-09-11 20:19:34 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix rq->core_pick corruption under core scheduling Core scheduling's pick_next_task() picks what to run on every SMT sibling of the core in a single pass under the shared core-wide rq lock. The selection state is consistent only while the lock is held continuously, so ->pick_task() originally could not release it. However, since 4c95380701f5 ("sched/ext: Fold balance_scx() into pick_task_scx()"), sched_ext runs dispatch from inside the pick and dispatching can drop the rq lock. To support this, pick_next_task() has been updated to restart the whole selection when a pick returns RETRY_TASK after releasing the lock. When selections on the same core interleave through the dropped lock, they corrupt each other's state: one clears the other's rq->core_pick leading to a NULL deref, or invalidates its keep-the-previous-task decision leaving a dequeued task running, which deadlocks the next wakeup and matches the reported hard hangs. A cookied ping-pong load on an SMT machine makes the interleavings frequent and kills the kernel within seconds. Fix it by making the pick return RETRY_TASK whenever dispatch released the rq lock, so that a selection only ever commits picks made under a continuously held lock. The previous patch's rq->scx.lock_drop_seq counts the releases. A dispatch that touched nothing never releases the lock and its verdict, including "nothing to run", stands: retries are bounded, each following a dispatch that actually did something, and an idle CPU does not loop. If another dispatch is already in flight on the rq, skip dispatching and pick from what is already queued locally - the in-flight dispatch has released the lock, so its own selection will retry and re-pick this rq, while returning RETRY_TASK here would only spin on the lock that dispatch needs to finish. Balance callbacks must run in the context that queued them, so they can only be queued on the CPU's own rq. When dispatching for another rq, run the deferred work directly instead - that rq may consume all its picks through the core-sched fast path and never queue the callback itself. The put_prev_task_scx() warning about a runnable task being left behind assumed that dispatch ran as part of the very pick that is switching away. That now only holds on the non-core path, so gate it and drop the cookie-match test, which is always true without core scheduling, from its condition.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 4c95380701f58b8112f0b891de8d160e4199e19d cdafb68155bee2d5c4e50c12e4606323e9334e6b git Not specified
CNA Linux Linux affected 4c95380701f58b8112f0b891de8d160e4199e19d d954004205c1a1d3f59ce8482b559266c15600fa git Not specified
CNA Linux Linux affected 6.19 Not specified
CNA Linux Linux unaffected 6.19 semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/cdafb68155bee2d5c4e50c12e4606323e9334e6b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d954004205c1a1d3f59ce8482b559266c15600fa 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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