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fat: Fix persisting directory entries on fsync(2) of the root directory

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Buffers containing the directory entries of a directory's children are
tracked in the directory inode's metadata bh list. Before commit
525da4f40a ("fat: Fix missed inode writeback during fsync(2)")
fsync(2) of a directory wrote that list out unconditionally via
mmb_fsync_noflush(). Now the list is written by
fat_sync_inode_metadata() which __writeback_single_inode() only
invokes when the inode has I_METADATA_WRITEBACK set. The root inode
never gets I_METADATA_WRITEBACK - __fat_write_inode() returns early
for it since the root directory has no directory entry of its own -
and fat_sync_inode_metadata() returns early for it as well. Hence
fsync(2) on the root directory returns success without writing out the
directory entries of its children.

Set I_METADATA_WRITEBACK for the root inode in __fat_write_inode() and
make fat_sync_inode_metadata() only skip the nonexistent directory
entry for the root inode but still sync the metadata bh list.

Fixes: 525da4f40a ("fat: Fix missed inode writeback during fsync(2)")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2026-07-27 17:16:43 +02:00
parent a50587bbf3
commit 28cb64a67b
1 changed files with 8 additions and 3 deletions
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11
fs/fat/inode.c
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@ -634,11 +634,12 @@ static int fat_sync_inode_metadata(struct inode *inode,
sector_t blocknr;
int offset;
/* The root directory has no directory entry of its own. */
if (inode->i_ino == MSDOS_ROOT_INO)
return 0;
goto sync_bhs;
i_pos = fat_i_pos_read(sbi, inode);
if (!i_pos)
return 0;
goto sync_bhs;
fat_get_blknr_offset(sbi, i_pos, &blocknr, &offset);
bh = sb_find_get_block_nonatomic(inode->i_sb, blocknr);
@ -654,6 +655,7 @@ static int fat_sync_inode_metadata(struct inode *inode,
}
}
brelse(bh);
sync_bhs:
return mmb_sync(&MSDOS_I(inode)->i_metadata_bhs);
}
@ -897,8 +899,11 @@ static int __fat_write_inode(struct inode *inode)
sector_t blocknr;
int offset;
if (inode->i_ino == MSDOS_ROOT_INO)
if (inode->i_ino == MSDOS_ROOT_INO) {
/* No entry to update but the metadata bh list may need syncing. */
set_inode_metadata_writeback(inode);
return 0;
}
retry:
i_pos = fat_i_pos_read(sbi, inode);