# CVE-2026-89520: sched/core: Make core-sched flips wait for in-flight selections

> A race condition in the Linux kernel core scheduler allows lock state corruption, potentially leading to system crashes or privilege escalation.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100676, BELL-CVE-2026-89520, DEBIAN-CVE-2026-89520, GHSA-q4pw-m5gm-wg9r, UBUNTU-CVE-2026-89520

## What is CVE-2026-89520?

CVE-2026-89520 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

sched/core: Make core-sched flips wait for in-flight selections

Core scheduling's pick_next_task() operates on all sibling rqs under one
acquisition of the shared core-wide lock. A ->pick_task() that releases the
rq lock leaves every sibling __lock momentarily free, letting
__sched_core_flip(false) complete mid-selection and rebind rq_lockp() under
it. The selection resumes on the split locks, touching sibling state it no
longer protects, and __schedule() finally releases a lock that was never
taken while leaking the one that was.

Count in-flight core-wide selections in the leader's rq->core_pick_in_flight
and make __sched_core_flip() wait for the count to drain. The count only
changes under the shared lock, which the flip holds while sampling, so no
other ordering is needed. The wait can repeat while selections overlap, but
the flip backs off between samples and flips are rare cookie-lifetime
events.

sched_core_cpu_deactivate() moves the count to the new leader - a stale copy
left behind would bias it forever if that CPU later returns as its own
leader.

## Which versions are affected by CVE-2026-89520?


## How do I fix CVE-2026-89520?

Apply the vendor's patch.

## Is CVE-2026-89520 being exploited?

There is no known exploitation of CVE-2026-89520 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89520 and fix it if it is affected.

What it is: CVE-2026-89520 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89520 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89520/ (Markdown: https://insights.sbomify.com/CVE-2026-89520/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89520
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89520
- OSV: https://osv.dev/vulnerability/CVE-2026-89520

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89520/
Summaries are generated and may contain mistakes; the official description above is the record.