---
id: CVE-2026-92502
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: clear stale xarray tags on folios skipped during writeback

  In data=journal mode, the writeback thread can hit the
  WARN_ON_ONCE(sb_rdonly(sb)) in ext4_journal_che…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: clear stale xarray tags on folios skipped during writeback

  In data=journal mode, the writeback thread can hit the
  WARN_ON_ONCE(sb_rdonly(sb)) in ext4_journal_che…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <
    f82a4929d0ef7ddf254c1c295ec1dfd24094f2de
  - >-
    Linux >= dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <
    a450ab88bfd57b227d72c7a3faad54d16c3fc099
  - >-
    Linux >= dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <
    aa0042630b1f7cab735b0a168539281198822586
  - >-
    Linux >= dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <
    43ae387c3ae6a11227d096669ddf883e27a39a11
  - >-
    Linux >= dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 <
    ec524aae479b4b2078c47492b90ec21200bce434
  - Linux 6.2
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:17:52.680'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-92502'
references:
  - url: 'https://git.kernel.org/stable/c/43ae387c3ae6a11227d096669ddf883e27a39a11'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a450ab88bfd57b227d72c7a3faad54d16c3fc099'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/aa0042630b1f7cab735b0a168539281198822586'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/ec524aae479b4b2078c47492b90ec21200bce434'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f82a4929d0ef7ddf254c1c295ec1dfd24094f2de'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.783Z'
epss: 0.00209
epssPercentile: 0.09783
---

## Overview

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

ext4: clear stale xarray tags on folios skipped during writeback

In data=journal mode, the writeback thread can hit the
WARN_ON_ONCE(sb_rdonly(sb)) in ext4_journal_check_start() while the
superblock is being remounted read-only during reboot:

Workqueue: writeback wb_workfn (flush-253:0)
RIP: 0010:ext4_journal_check_start+0x8b/0xd0
Call Trace:
  __ext4_journal_start_sb+0x3c/0x1e0
  mpage_prepare_extent_to_map+0x4af/0x580
  ext4_do_writepages+0x3c0/0x1080
  ext4_writepages+0xc8/0x1a0
  do_writepages+0xc4/0x180
  __writeback_single_inode+0x45/0x2f0
  writeback_sb_inodes+0x26b/0x5d0
  __writeback_inodes_wb+0x54/0x100
  wb_writeback+0x1ac/0x320
  wb_workfn+0x394/0x470

And followed by the warning:
EXT4-fs warning (device vda1): ext4_evict_inode:195: inode #6263:
comm (sd-umount): data will be lost

This issue is not reproduced every time, but frequently.
The reproduction step is to create a VM with 8 CPUs, 16G memory and
setup data=journal:
sudo tune2fs -o journal_data /dev/vda1
Run fio:
rm -f fiotest
fio --name=fiotest --rw=randwrite --bs=4k --runtime=6 --ioengine=libaio
--iodepth=256 --numjobs=8 --filename=fiotest --filesize=30G
--group_reporting
Reboot the VM, and check the console output from:
virsh console testvm

But there is no dirty inode, folio_clear_dirty_for_io clears PG_dirty
but leaves tags PAGECACHE_TAG_DIRTY and PAGECACHE_TAG_TOWRITE set which
are only cleared by __folio_start_writeback.
In data=journal mode, jbd2 checkpoints the journalled data to its final
location and clears its own dirty flag without touching folio PG_dirty
or xarray dirty flags.
The commit f4a2b42e7891 ("ext4: fix stale xarray tags after writeback")
fixes when PG_dirty is still set but there is no dirty page.
Another case is PG_dirty is cleared, but PAGECACHE_TAG_DIRTY and
PAGECACHE_TAG_TOWRITE is still set. In this case, writeback thread
checks clean folio and skips it in mpage_prepare_extent_to_map:
if (!folio_test_dirty(folio) ||
    ...
        folio_unlcok(folio);
	continue

And never reaches ext4_bio_write_folio where the commit f4a2b42e7891
clears the stale xarray tags. Print debug logs after the filesystem
is remounted read-only:
writepages RDONLY nrpages=2048 dirtytag=1 wbtag=0 towrite=1 sync=0
And all folios are actually clean:
folio idx=3 dirty=0 wb=0 checked=0 dirtybuf=0 jbddirty=0 mapped=1
...

We need to clear the xarray stale tags for such clean folios by
cycling them through writeback in the skip path, the same way
f4a2b42e7891 does in ext4_bio_write_folio.

## Remediation

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