# CVE-2021-47189: btrfs: fix memory ordering between normal and ordered work functions

> A race condition in the Linux kernel's btrfs filesystem can cause system crashes due to improper memory ordering between work functions.

- **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:** 10 Apr 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-47189, GHSA-3wrv-h289-483m, UBUNTU-CVE-2021-47189

## What is CVE-2021-47189?

CVE-2021-47189 is a high-severity vulnerability in Linux kernel, published on 10 Apr 2024. 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:

btrfs: fix memory ordering between normal and ordered work functions

Ordered work functions aren't guaranteed to be handled by the same thread
which executed the normal work functions. The only way execution between
normal/ordered functions is synchronized is via the WORK_DONE_BIT,
unfortunately the used bitops don't guarantee any ordering whatsoever.

This manifested as seemingly inexplicable crashes on ARM64, where
async_chunk::inode is seen as non-null in async_cow_submit which causes
submit_compressed_extents to be called and crash occurs because
async_chunk::inode suddenly became NULL. The call trace was similar to:

    pc : submit_compressed_extents+0x38/0x3d0
    lr : async_cow_submit+0x50/0xd0
    sp : ffff800015d4bc20

    <registers omitted for brevity>

    Call trace:
     submit_compressed_extents+0x38/0x3d0
     async_cow_submit+0x50/0xd0
     run_ordered_work+0xc8/0x280
     btrfs_work_helper+0x98/0x250
     process_one_work+0x1f0/0x4ac
     worker_thread+0x188/0x504
     kthread+0x110/0x114
     ret_from_fork+0x10/0x18

Fix this by adding respective barrier calls which ensure that all
accesses preceding setting of WORK_DONE_BIT are strictly ordered before
setting the flag. At the same time add a read barrier after reading of
WORK_DONE_BIT in run_ordered_work which ensures all subsequent loads
would be strictly ordered after reading the bit. This in turn ensures
are all accesses before WORK_DONE_BIT are going to be strictly ordered
before any access that can occur in ordered_func.

## Which versions are affected by CVE-2021-47189?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47189?

Apply the vendor's patch.

## Is CVE-2021-47189 being exploited?

There is no known exploitation of CVE-2021-47189 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47189 and fix it if it is affected.

What it is: CVE-2021-47189 is a high-severity vulnerability in Linux kernel, published on 10 Apr 2024. 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-2021-47189 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2021-47189/ (Markdown: https://insights.sbomify.com/CVE-2021-47189/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47189
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47189
- OSV: https://osv.dev/vulnerability/CVE-2021-47189

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47189/
Summaries are generated and may contain mistakes; the official description above is the record.