---
id: CVE-2026-98536
title: 'writeback: report a Tasks-RCU quiescent state per cgwb drain pass'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  writeback: report a Tasks-RCU quiescent state per cgwb drain pass

  cleanup_offline_cgwbs_workfn() drains a dying cgwb by calling
  cleanup_offline_cgwb() until it returns…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 <
    863049b4018237d1590cd13b16e9fe9c0faad2c6
  - >-
    Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 <
    42462b5bb0dec57db7f85d0f77655c737d45754d
  - >-
    Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 <
    ebf1555ad2821be06f87a88ffd9a2cab8d2200e1
  - >-
    Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 <
    4eb889649eaf65f4a5727b04ba1c017b7d05bb16
  - >-
    Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 <
    fd3bf32279df98751364b3609eb100a3e42f253b
  - >-
    Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 <
    260f586a80e7f624dd7f069898a75a904f34d373
  - >-
    Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 <
    407a5d205179a4ab186571b0e16ec42725dc77bc
  - Linux 5.14
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:18:04.013Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98536'
references:
  - url: 'https://git.kernel.org/stable/c/863049b4018237d1590cd13b16e9fe9c0faad2c6'
  - url: 'https://git.kernel.org/stable/c/42462b5bb0dec57db7f85d0f77655c737d45754d'
  - url: 'https://git.kernel.org/stable/c/ebf1555ad2821be06f87a88ffd9a2cab8d2200e1'
  - url: 'https://git.kernel.org/stable/c/4eb889649eaf65f4a5727b04ba1c017b7d05bb16'
  - url: 'https://git.kernel.org/stable/c/fd3bf32279df98751364b3609eb100a3e42f253b'
  - url: 'https://git.kernel.org/stable/c/260f586a80e7f624dd7f069898a75a904f34d373'
  - url: 'https://git.kernel.org/stable/c/407a5d205179a4ab186571b0e16ec42725dc77bc'
tags:
  - cve.org
ingestedAt: '2026-10-18T15:45:12.277Z'
---

## Overview

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

writeback: report a Tasks-RCU quiescent state per cgwb drain pass

cleanup_offline_cgwbs_workfn() drains a dying cgwb by calling
cleanup_offline_cgwb() until it returns false, with a cond_resched()
between passes.  On a CONFIG_PREEMPTION kernel that cond_resched() does
nothing: _cond_resched() is a plain "return 0", and under PREEMPT_DYNAMIC
the full and lazy modes disable it.  Since commit 7dadeaa6e851 ("sched:
Further restrict the preemption modes") those are the only two models on
the architectures with PREEMPT_LAZY support, arm64 and x86 among them, so
the drain loop never reports a Tasks-RCU quiescent state.

A worker draining a cgwb with millions of attached inodes runs for
minutes.  On a 6.18 arm64 host in lazy mode the cgwb worker drained one
dying cgroup's writeback domain for over 11 minutes.  A BPF program unlink
(bpf_trampoline_unlink_prog -> bpf_trampoline_update ->
unregister_ftrace_direct -> ftrace_shutdown -> synchronize_rcu_tasks())
waited on that grace period while holding the trampoline mutex, 42 tasks
queued behind it in D state, and the hung task detector fired at 614 s and
panicked the host.  Any BPF or ftrace detach during a long drain inherits
the drain's length.

Fix this by calling cond_resched_tasks_rcu_qs() so we do not stall out
anybody who calls sycnrhonize_rcu_tasks().  We put this in a do { } while
loop because if we have many small cgroups cleanup_offline_cgwb() will
return false and we will never call cond_resched_tasks_rcu_qs(), creating
the same problem.

## Affected

- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 863049b4018237d1590cd13b16e9fe9c0faad2c6`
- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 42462b5bb0dec57db7f85d0f77655c737d45754d`
- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < ebf1555ad2821be06f87a88ffd9a2cab8d2200e1`
- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 4eb889649eaf65f4a5727b04ba1c017b7d05bb16`
- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < fd3bf32279df98751364b3609eb100a3e42f253b`
- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 260f586a80e7f624dd7f069898a75a904f34d373`
- `Linux >= c22d70a162d3cc177282c4487be4d54876ca55c8 < 407a5d205179a4ab186571b0e16ec42725dc77bc`
- `Linux 5.14`

## Remediation

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