ext4: clear stale xarray tags on folios skipped during writeback

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-92502
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:17:52 UTC
Updated2026-10-19 10:16:50 UTC
DescriptionIn 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.

Risk And Classification

EPSS: 0.001680000 probability, percentile 0.064610000 (date 2026-09-18)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 f82a4929d0ef7ddf254c1c295ec1dfd24094f2de git Not specified
CNA Linux Linux affected dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 a450ab88bfd57b227d72c7a3faad54d16c3fc099 git Not specified
CNA Linux Linux affected dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 aa0042630b1f7cab735b0a168539281198822586 git Not specified
CNA Linux Linux affected dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 43ae387c3ae6a11227d096669ddf883e27a39a11 git Not specified
CNA Linux Linux affected dff4ac75eeeefc4397fe7cf8ce559425bf46b1f7 ec524aae479b4b2078c47492b90ec21200bce434 git Not specified
CNA Linux Linux affected 6.2 Not specified
CNA Linux Linux unaffected 6.2 semver Not specified
CNA Linux Linux unaffected 6.6.157 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.110 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.52 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/a450ab88bfd57b227d72c7a3faad54d16c3fc099 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/43ae387c3ae6a11227d096669ddf883e27a39a11 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/aa0042630b1f7cab735b0a168539281198822586 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ec524aae479b4b2078c47492b90ec21200bce434 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f82a4929d0ef7ddf254c1c295ec1dfd24094f2de 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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