---
id: CVE-2025-39953
title: 'cgroup: split cgroup_destroy_wq into 3 workqueues'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  cgroup: split cgroup_destroy_wq into 3 workqueues

  A hung task can occur during [1] LTP cgroup testing when repeatedly
  mounting/unmounting perf_event and net_prio contr…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    cabadd7fd15f97090f752fd22dd7f876a0dc3dc4
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    a0c896bda7077aa5005473e2c5b3c27173313b4c
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    f2795d1b92506e3adf52a298f7181032a1525e04
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    993049c9b1355c78918344a6403427d53f9ee700
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    4a1e3ec28e8062cd9f339aa6a942df9c5bcb6811
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    ded4d207a3209a834b6831ceec7f39b934c74802
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    05e0b03447cf215ec384210441b34b7a3b16e8b0
  - >-
    Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 <
    79f919a89c9d06816dbdbbd168fa41d27411a7f9
  - Linux 4.6
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-06-10T20:41:56.498338Z'
published: '2025-10-04'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:42:34.700Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-39953'
references:
  - url: 'https://git.kernel.org/stable/c/cabadd7fd15f97090f752fd22dd7f876a0dc3dc4'
  - url: 'https://git.kernel.org/stable/c/a0c896bda7077aa5005473e2c5b3c27173313b4c'
  - url: 'https://git.kernel.org/stable/c/f2795d1b92506e3adf52a298f7181032a1525e04'
  - url: 'https://git.kernel.org/stable/c/993049c9b1355c78918344a6403427d53f9ee700'
  - url: 'https://git.kernel.org/stable/c/4a1e3ec28e8062cd9f339aa6a942df9c5bcb6811'
  - url: 'https://git.kernel.org/stable/c/ded4d207a3209a834b6831ceec7f39b934c74802'
  - url: 'https://git.kernel.org/stable/c/05e0b03447cf215ec384210441b34b7a3b16e8b0'
  - url: 'https://git.kernel.org/stable/c/79f919a89c9d06816dbdbbd168fa41d27411a7f9'
tags:
  - cve.org
epss: 0.0015
epssPercentile: 0.03483
ingestedAt: '2026-09-08T15:33:26.996Z'
---

## Overview

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

cgroup: split cgroup_destroy_wq into 3 workqueues

A hung task can occur during [1] LTP cgroup testing when repeatedly
mounting/unmounting perf_event and net_prio controllers with
systemd.unified_cgroup_hierarchy=1. The hang manifests in
cgroup_lock_and_drain_offline() during root destruction.

Related case:
cgroup_fj_function_perf_event cgroup_fj_function.sh perf_event
cgroup_fj_function_net_prio cgroup_fj_function.sh net_prio

Call Trace:
	cgroup_lock_and_drain_offline+0x14c/0x1e8
	cgroup_destroy_root+0x3c/0x2c0
	css_free_rwork_fn+0x248/0x338
	process_one_work+0x16c/0x3b8
	worker_thread+0x22c/0x3b0
	kthread+0xec/0x100
	ret_from_fork+0x10/0x20

Root Cause:

CPU0                            CPU1
mount perf_event                umount net_prio
cgroup1_get_tree                cgroup_kill_sb
rebind_subsystems               // root destruction enqueues
				// cgroup_destroy_wq
// kill all perf_event css
                                // one perf_event css A is dying
                                // css A offline enqueues cgroup_destroy_wq
                                // root destruction will be executed first
                                css_free_rwork_fn
                                cgroup_destroy_root
                                cgroup_lock_and_drain_offline
                                // some perf descendants are dying
                                // cgroup_destroy_wq max_active = 1
                                // waiting for css A to die

Problem scenario:
1. CPU0 mounts perf_event (rebind_subsystems)
2. CPU1 unmounts net_prio (cgroup_kill_sb), queuing root destruction work
3. A dying perf_event CSS gets queued for offline after root destruction
4. Root destruction waits for offline completion, but offline work is
   blocked behind root destruction in cgroup_destroy_wq (max_active=1)

Solution:
Split cgroup_destroy_wq into three dedicated workqueues:
cgroup_offline_wq – Handles CSS offline operations
cgroup_release_wq – Manages resource release
cgroup_free_wq – Performs final memory deallocation

This separation eliminates blocking in the CSS free path while waiting for
offline operations to complete.

[1] https://github.com/linux-test-project/ltp/blob/master/runtest/controllers

## Affected

- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < cabadd7fd15f97090f752fd22dd7f876a0dc3dc4`
- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < a0c896bda7077aa5005473e2c5b3c27173313b4c`
- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < f2795d1b92506e3adf52a298f7181032a1525e04`
- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < 993049c9b1355c78918344a6403427d53f9ee700`
- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < 4a1e3ec28e8062cd9f339aa6a942df9c5bcb6811`
- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < ded4d207a3209a834b6831ceec7f39b934c74802`
- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < 05e0b03447cf215ec384210441b34b7a3b16e8b0`
- `Linux >= 334c3679ec4b2b113c35ebe37d2018b112dd5013 < 79f919a89c9d06816dbdbbd168fa41d27411a7f9`
- `Linux 4.6`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.