# CVE-2026-99256: dm cache: fix issue with background work locking

Status: published. Published: 2026-11-03. Updated: 2026-11-03.

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

dm cache: fix issue with background work locking

dm cache used a rw_semaphore for background_work_lock. Write locks on
rw_semaphores have strict owner semantics, but there was no guarantee
that the process that locked background_work_lock was the same process
that unlocked it. This can be easily seen using a kernel compiled with
CONFIG_DEBUG_RWSEMS. Given a dm cache device <cache>, run: 'dmsetup
suspend <cache> && dmsetup resume <cache>'. This will trigger a kernel
warning:

DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))

triggered by cache_resume(). To fix this, switch from a rw_semaphore to
a spinlock and a wait queue. dm cache already has a wait queue and
associated counter, migration_wait and nr_allocated_migrations, that was
getting woken up when background work was getting completed, but wasn't
actually used by anything. This is replaced by the background_work queue
and counter.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < 0c7a8cad7c96012a9157a189649e569d0390f384 (affected, git); ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < f5db935d257023c3ef410bd39163b949b0e5a55d (affected, git); ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < 6290507ecc0dd6dd40759729cbbbd49b1d2a63c4 (affected, git); ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < 8433fd005c25fd127021f67c9144a879fb585572 (affected, git); ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < 2f2cfa16dd0f4179bb988139dd37d00a42324f6c (affected, git); ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < 73df2ff409f3db95029982fe3656329568e3715d (affected, git); ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < 104f09e02038b0fc6bbb718b3976af029e15c1d0 (affected, git); ≥ b29d4986d0da1a27cd35917cdb433672f5c95d7f; < bc9781c0247de107876f32929f1637db93a42b34 (affected, git). Source: CNA: Linux
- Linux / Linux: 4.12 (affected); ≥ 0; < 4.12 (unaffected, semver); ≥ 5.10.273; ≤ 5.10.* (unaffected, semver); ≥ 5.15.224; ≤ 5.15.* (unaffected, semver); ≥ 6.1.191; ≤ 6.1.* (unaffected, semver); ≥ 6.6.161; ≤ 6.6.* (unaffected, semver); ≥ 6.12.115; ≤ 6.12.* (unaffected, semver); ≥ 6.18.59; ≤ 6.18.* (unaffected, semver); ≥ 7.2.13; ≤ 7.2.* (unaffected, semver); ≥ 7.3; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/0c7a8cad7c96012a9157a189649e569d0390f384 (CNA: Linux)

- https://git.kernel.org/stable/c/f5db935d257023c3ef410bd39163b949b0e5a55d (CNA: Linux)

- https://git.kernel.org/stable/c/6290507ecc0dd6dd40759729cbbbd49b1d2a63c4 (CNA: Linux)

- https://git.kernel.org/stable/c/8433fd005c25fd127021f67c9144a879fb585572 (CNA: Linux)

- https://git.kernel.org/stable/c/2f2cfa16dd0f4179bb988139dd37d00a42324f6c (CNA: Linux)

- https://git.kernel.org/stable/c/73df2ff409f3db95029982fe3656329568e3715d (CNA: Linux)

- https://git.kernel.org/stable/c/104f09e02038b0fc6bbb718b3976af029e15c1d0 (CNA: Linux)

- https://git.kernel.org/stable/c/bc9781c0247de107876f32929f1637db93a42b34 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-99256; retrieved 2026-11-03; source updated 2026-11-03

Revision: bfb46b1bbf40b160ec3848a64271484515fee2aa72bfab416ccd47f51b19a779

Canonical: https://y2.dev/cve/CVE-2026-99256

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