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.
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.
Metrics
Affected Vendors & Products
Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Thu, 17 Sep 2026 16:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | ext4: clear stale xarray tags on folios skipped during writeback | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-17T16:10:15.399Z
Reserved: 2026-09-16T12:21:13.872Z
Link: CVE-2026-92502
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-17T17:17:52.680
Modified: 2026-09-17T17:17:52.680
Link: CVE-2026-92502
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.