# CVE-2026-89521: sched/core: Handle pick_task() releasing the rq lock

> A race condition in the Linux kernel scheduler can cause accounting errors and potential denial of service when the runqueue lock is released during task selection.

- **Severity:** High 7.3 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/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:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-89521, GHSA-2jj9-3xxj-4v43, UBUNTU-CVE-2026-89521

## What is CVE-2026-89521?

CVE-2026-89521 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: Handle pick_task() releasing the rq lock

Core scheduling's pick_next_task() breaks when a ->pick_task()
implementation can release the rq lock. The selection state derived on entry
is only valid while the lock is held continuously. Once a pick can drop the
lock, an interleaving selection can invalidate all of it: the single-CPU
fast path can commit an uncookied pick although the core went cookied during
the release, and forceidle committed by the interleaving selection skews the
restarted pass's accounting.

Fix it by restarting the whole selection when a pick returns RETRY_TASK
after releasing the lock: a single restart point above the state derivation
replaces the per-loop restart labels, so a retry picks up state committed by
interleaving selections and accounts and resets forceidle like a fresh
selection would.

need_sync and fi_before latch across retries. Clock validity can't be
re-derived - there is no program-ordered way to tell whether the own and
core rq clocks are still updated after the lock was released, as other
lockers' pin cycles may or may not have invalidated them. When restarting,
clear core_clock_updated so that the sibling loop re-updates the core rq,
and update the own rq clock if invalidated.

## Which versions are affected by CVE-2026-89521?


## How do I fix CVE-2026-89521?

Apply the vendor's patch.

## Is CVE-2026-89521 being exploited?

There is no known exploitation of CVE-2026-89521 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89521 and fix it if it is affected.

What it is: CVE-2026-89521 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-2026-89521 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-2026-89521/ (Markdown: https://insights.sbomify.com/CVE-2026-89521/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89521
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89521
- OSV: https://osv.dev/vulnerability/CVE-2026-89521

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89521/
Summaries are generated and may contain mistakes; the official description above is the record.