CVE-2026-89517 — sched_ext: Fix rq->core_pick corruption under core scheduling
In 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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+1
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
EPSS over time FIRST
Oct 15, 2026 → Oct 22, 2026 · 7 reading(s) · max 0.20%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Not enough vector or weakness data: use the affected application’s logs as a starting point.
Timeline
What happened to this CVE, newest first.
- 2026
- Record published
- Affected products added · linux/linux
- Source status changed · → Received
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× References added · Oct 19, 2026 – Oct 19, 2026
- 1× Official description updated · Oct 15, 2026 – Oct 15, 2026
References
4 on the record
Elsewhere on this site
Related CVEs (same products)
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- Unknown CVE-2026-99084 readdir: take no inode lock on an immutable directory 10h
- Unknown CVE-2026-99079 net/mlx5e: Prevent stale XSK buffer release on refill retry 10h
- Unknown CVE-2026-99080 fs: Free any excess xarray nodes in clear_inode() 10h
- Unknown CVE-2026-99081 bnxt_en: fix DMA mapping length for padded small packets 10h
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CVSS score published by NVD, the CNA, CISA or GitHub so far.
- No fixed version, patch or mitigation documented.
- No CISA SSVC assessment.
- No CWE classification.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-89517 is "sched_ext: Fix rq->core_pick corruption under core scheduling", rated Unknown. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. EPSS 0.20% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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