# CVE-2026-80719: mm: mglru: fix stale batch updates after memcg reparenting

> A race condition in the Linux kernel MGLRU subsystem can cause premature Out-of-Memory kills, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Aug 2026
- **Updated:** 28 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-80719, GHSA-5jwv-p5cj-5p3c, UBUNTU-CVE-2026-80719

## What is CVE-2026-80719?

CVE-2026-80719 is a denial of service vulnerability in Linux, published on 28 Aug 2026. 

### Official description

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

mm: mglru: fix stale batch updates after memcg reparenting

The mglru page table walker batches per-generation size deltas in
walk->nr_pages while walking page tables without holding the lruvec lock. 
The reset_batch_size() later folds those deltas into walk->lruvec under
the lruvec lock.

The page table walker can run concurrently with the memcg reparenting path
as follows:

CPU0                           CPU1
====                           ====

walk_mm
--> walk_page_range
    --> update_batch_size
        --> walk->nr_pages += delta

                              mem_cgroup_css_offline
                              --> memcg_reparent_objcgs
                                  --> lock lruvec
                                      lru_gen_reparent_memcg
                                      --> reparent child folios to parent
                                      unlock lruvec

    lock lruvec
    reset_batch_size
    --> child lrugen->nr_pages += delta

This will trigger the following warning in lru_gen_exit_memcg():

	VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0,
				   sizeof(lruvec->lrugen.nr_pages)));

And the user-visible impact of underestimated nr_pages in MGLRU was
premature OOMs because MGLRU does not try to reclaim memory when nr_pages
reaches zero, but there are still more pages.

To fix it, make reset_batch_size() check CSS_DYING under RCU before
flushing the pending batch.  A non-dying memcg keeps the original lruvec
stable against RCU-delayed offlining; a dying memcg redirects the deltas
to the first non-dying ancestor.

## Which versions are affected by CVE-2026-80719?


## How do I fix CVE-2026-80719?

Apply the vendor's patch.

## Is CVE-2026-80719 being exploited?

There is no known exploitation of CVE-2026-80719 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80719 and fix it if it is affected.

What it is: CVE-2026-80719 is a denial of service vulnerability in Linux, published on 28 Aug 2026. 
Exploitation: There is no known exploitation of CVE-2026-80719 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-2026-80719/ (Markdown: https://insights.sbomify.com/CVE-2026-80719/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80719
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80719
- OSV: https://osv.dev/vulnerability/CVE-2026-80719

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80719/
Summaries are generated and may contain mistakes; the official description above is the record.