# CVE-2026-90265: btrfs: defrag: fix deadlock between defrag and delalloc space reservation
> A deadlock in the Linux kernel btrfs filesystem can cause a denial of service when defrag and delalloc space reservation interact.
- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102024, BELL-CVE-2026-90265, DEBIAN-CVE-2026-90265, GHSA-hrjh-vpgf-4c95, UBUNTU-CVE-2026-90265
## What is CVE-2026-90265?
CVE-2026-90265 is a denial of service vulnerability in Linux, published on 17 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:
btrfs: defrag: fix deadlock between defrag and delalloc space reservation
While running fsstress with autodefrag and flushoncommit, hit a deadlock
due to the fact that defrag reserves delalloc space while it's holding
dirty and locked folios, besides the extent range lock. The stack traces
are the following:
[958.624] task:kworker/u50:3 state:D stack:0 pid:20365 tgid:20365 ppid:2 task_flags:0x4208060 flags:0x00080000
[958.626] Workqueue: events_unbound btrfs_async_reclaim_metadata_space [btrfs]
[958.627] Call Trace:
[958.628]
[958.628] __schedule+0x4be/0x10f0
[958.629] ? preempt_count_add+0x69/0xa0
[958.630] schedule+0x26/0xd0
[958.631] wait_current_trans+0x102/0x160 [btrfs]
[958.632] ? __pfx_autoremove_wake_function+0x10/0x10
[958.633] start_transaction+0x374/0x900 [btrfs]
[958.634] btrfs_commit_current_transaction+0x1d/0x70 [btrfs]
[958.635] flush_space+0xca/0x5e0 [btrfs]
[958.636] ? _raw_spin_unlock+0x15/0x30
[958.637] ? btrfs_reduce_alloc_profile+0x8c/0x190 [btrfs]
[958.639] ? _raw_spin_unlock+0x15/0x30
[958.640] ? calc_available_free_space.isra.0+0x6f/0x110 [btrfs]
[958.641] do_async_reclaim_metadata_space+0x84/0x190 [btrfs]
[958.642] btrfs_async_reclaim_metadata_space+0x64/0x80 [btrfs]
[958.644] process_one_work+0x19d/0x3a0
[958.644] worker_thread+0x1c4/0x330
[958.645] ? __pfx_worker_thread+0x10/0x10
[958.646] kthread+0xfc/0x130
[958.647] ? __pfx_kthread+0x10/0x10
[958.648] ret_from_fork+0x1f7/0x2c0
[958.648] ? __pfx_kthread+0x10/0x10
[958.649] ret_from_fork_asm+0x1a/0x30
[958.650]
[958.651] task:kworker/u49:7 state:D stack:0 pid:52990 tgid:52990 ppid:2 task_flags:0x4208060 flags:0x00080000
[958.653] Workqueue: writeback wb_workfn (flush-btrfs-334)
[958.655] Call Trace:
[958.655]
[958.656] __schedule+0x4be/0x10f0
[958.657] ? __blk_flush_plug+0xe9/0x140
[958.658] schedule+0x26/0xd0
[958.658] io_schedule+0x42/0x70
[958.659] folio_wait_bit_common+0x12b/0x330
[958.660] ? folio_wait_bit_common+0x100/0x330
[958.662] ? __pfx_wake_page_function+0x10/0x10
[958.663] extent_write_cache_pages+0x599/0x830 [btrfs]
[958.664] ? acpi_fwnode_get_reference_args+0x1fa/0x270
[958.665] btrfs_writepages+0x77/0x130 [btrfs]
[958.666] ? __pfx_end_bbio_data_write+0x10/0x10 [btrfs]
[958.667] do_writepages+0xc6/0x160
[958.668] __writeback_single_inode+0x42/0x310
[958.669] writeback_sb_inodes+0x231/0x570
[958.670] wb_writeback+0x8a/0x340
[958.671] wb_workfn+0xbf/0x450
[958.672] ? finish_task_switch.isra.0+0xc1/0x350
[958.673] process_one_work+0x19d/0x3a0
[958.673] worker_thread+0x1c4/0x330
[958.674] ? __pfx_worker_thread+0x10/0x10
[958.675] kthread+0xfc/0x130
[958.676] ? __pfx_kthread+0x10/0x10
[958.676] ret_from_fork+0x1f7/0x2c0
[958.677] ? __pfx_kthread+0x10/0x10
[958.678] ret_from_fork_asm+0x1a/0x30
[958.679]
[958.679] task:btrfs-cleaner state:D stack:0 pid:296750 tgid:296750 ppid:2 task_flags:0x208040 flags:0x00080000
[958.681] Call Trace:
[958.682]
[958.682] __schedule+0x4be/0x10f0
[958.683] schedule+0x26/0xd0
[958.684] handle_reserve_ticket+0x1b9/0x2c0 [btrfs]
[958.685] ? __pfx_autoremove_wake_function+0x10/0x10
[958.686] reserve_bytes+0x283/0x4c0 [btrfs]
[958.687] btrfs_reserve_metadata_bytes+0x18/0xb0 [btrfs]
[958.688] btrfs_delalloc_reserve_metadata+0x121/0x320 [btrfs]
[958.690] btrfs_delalloc_reserve_space+0x46/0xb0 [btrfs]
[958.691] btrfs_defrag_file+0x903/0x1110 [btrfs]
[958.692] btrfs_run_defrag_inodes+0x334/0x430 [btrfs]
[958.694] cleaner_kthread+0x97/0x1c0 [btrfs]
[958.694] ? __pfx_cleaner_kthread+0x10/0x10 [btrfs]
[958.696] kthread+0xfc/0x130
[958.696] ? __pfx_kthread+0x10/0x10
[958.697] ret_
---truncated---
## Which versions are affected by CVE-2026-90265?
## How do I fix CVE-2026-90265?
Apply the vendor's patch.
## Is CVE-2026-90265 being exploited?
There is no known exploitation of CVE-2026-90265 in the wild and no public exploit code.
## Fix prompt for AI coding agents
```text
Check this codebase for CVE-2026-90265 and fix it if it is affected.
What it is: CVE-2026-90265 is a denial of service vulnerability in Linux, published on 17 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-2026-90265 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-2026-90265/ (Markdown: https://insights.sbomify.com/CVE-2026-90265/index.md)
```
## Sources
- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90265
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90265
- OSV: https://osv.dev/vulnerability/CVE-2026-90265
---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90265/
Summaries are generated and may contain mistakes; the official description above is the record.