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ntfs: fix $MFTMirr write offset when it spans multiple folios

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When commit 115380f9a2 ("ntfs: update mft operations") refactored the
MFT code to use folios, it assumed $MFTMirr is allocated contiguously,
which is indeed what mkfs arranges.  However, the folio rewrite kept a
leftover from the old buffer-head/runlist based implementation:
vol->cluster_size_mask is still applied to the mirror write offset.
In fact it is no longer needed -- and in some configurations it is
actively wrong.

The bug triggers whenever the four mirror records do not fit in a
single folio, i.e. when mft_record_size exceeds PAGE_SIZE / 4 (for
example mft_record_size > 1KiB on 4KiB pages).

For example, on the built-in 4Kn SSD (Apple SSD AP0256J) of a
MacBookPro14,1 with 4096-byte MFT records, mirror record 3 is still
written to the location of record 0.  $MFTMirr therefore gets out of
sync with $MFT and the following warning is printed on remount:

        ntfs: (device nvme0n1p3): check_mft_mirror(): $MFT and $MFTMirr
              record 0 do not match.  Run chkdsk.

Fix it by always adding the folio offset (folio->index << PAGE_SHIFT)
to the base LCN address instead of applying the cluster_size_mask
truncation.  This is the standard file-offset calculation and is
correct for every combination of cluster size, page size and MFT
record size, provided $MFTMirr data is contiguous from mftmirr_lcn
(which mkfs always arranges).

Tested on the volume above: before the change mirror records 1-3 are
all written to record 0's sector; after the change the write-back
probe reports:

        ntfs: NTFSDBG pre mft_no=0x3 folio_idx=0x3 ofs=0x0 mftmirr_lcn=0x2540c5 clu_bits=12 rec_bits=12 PAGE_SHIFT=12 sect=0x12a0640
        ntfs: NTFSDBG pre mft_no=0x0 folio_idx=0x0 ofs=0x0 mftmirr_lcn=0x2540c5 clu_bits=12 rec_bits=12 PAGE_SHIFT=12 sect=0x12a0628

which matches the expected sectors computed as:

        (NTFS_CLU_TO_B(mftmirr_lcn) + (folio->index << PAGE_SHIFT)) >> SECTOR_SHIFT

        record 0: (0x2540c5 << 12) + 0x0000 = 0x2540c5000 >> 9 = 0x12a0628
        record 3: (0x2540c5 << 12) + 0x3000 = 0x2540c8000 >> 9 = 0x12a0640

A 13 MB file write succeeds on this volume and the file is byte-for-byte
identical after a umount/mount cycle.

Fixes: 115380f9a2 ("ntfs: update mft operations")
Assisted-by: UOS-AI
Assisted-by: CodeBuddy:Hy4 preview
Signed-off-by: Zhu Tianhao <zhutianhao75@hotmail.com>
Reviewed-by: Baolin Liu <liubaolin@kylinos.cn>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
This commit is contained in:
Zhu Tianhao 2026-09-08 05:41:00 +09:00 committed by Namjae Jeon
parent 0c32a42fd9
commit 229e818830
1 changed files with 3 additions and 7 deletions
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10
fs/ntfs/mft.c
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@ -463,7 +463,7 @@ int ntfs_sync_mft_mirror(struct ntfs_volume *vol, const u64 mft_no,
{
u8 *kmirr;
struct folio *folio;
unsigned int folio_ofs, lcn_folio_off = 0;
unsigned int folio_ofs;
int err = 0;
struct bio *bio;
@ -493,15 +493,11 @@ int ntfs_sync_mft_mirror(struct ntfs_volume *vol, const u64 mft_no,
memcpy(kmirr, m, vol->mft_record_size);
kunmap_local(kmirr);
if (vol->cluster_size_bits > PAGE_SHIFT) {
lcn_folio_off = folio->index << PAGE_SHIFT;
lcn_folio_off &= vol->cluster_size_mask;
}
bio = bio_alloc(vol->sb->s_bdev, 1, REQ_OP_WRITE, GFP_NOIO);
bio->bi_iter.bi_sector =
ntfs_bytes_to_bio_sector(NTFS_CLU_TO_B(vol, vol->mftmirr_lcn) +
lcn_folio_off + folio_ofs);
((u64)folio->index << PAGE_SHIFT) +
folio_ofs);
if (bio_add_folio(bio, folio, vol->mft_record_size, folio_ofs))
err = submit_bio_wait(bio);