[PATCH v10 5/6] ntfs: do not clear the volume dirty bit during sync

[Hongling Zeng]

ntfs_sync_fs() clears VOLUME_IS_DIRTY while the volume is still mounted
read-write, so a sync running concurrently with an in-flight metadata
modification can clear and persist a bit that was just set: the
modification then lands on a volume that is clean on disk, and a crash
does not run chkdsk.  Closing this from the writer side would mean
holding the $Volume mrec_lock across the whole operation.

Drop the ntfs_sync_fs() persistence point and leave the clearing to the
remount-to-read-only path, which the VFS reaches only after
sb_prepare_remount_readonly() has drained in-flight writers, and to
ntfs_put_super(), which runs after evict_inodes() on a quiesced
filesystem.  A mounted read-write volume now keeps the dirty bit until
it is dismounted cleanly, which matches the NTFS semantics; the cost is
a needless chkdsk if the machine crashes between a sync and the unmount.

Reported-by: Baolin Liu <liubaolin@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hongling Zeng <zenghongling@xxxxxxxxxx>
---
 fs/ntfs/super.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
index 3574c224fe28..f58b9cd86b27 100644
--- a/fs/ntfs/super.c
+++ b/fs/ntfs/super.c
@@ -1963,11 +1963,14 @@ static int ntfs_sync_fs(struct super_block *sb, int wait)
 	if (!wait)
 		return 0;
 
-	/* If there are some dirty buffers in the bdev inode */
-	if (ntfs_sync_volume_dirty_state(vol)) {
-		ntfs_warning(sb, "Failed to sync dirty bit in volume information flags.  Run chkdsk.");
-		err = -EIO;
-	}
+	/*
+	 * The volume dirty bit is deliberately not cleared here: a sync
+	 * running concurrently with an in-flight modification could clear
+	 * and persist a bit that was just set, leaving the modification
+	 * on a volume that is clean on disk.  The bit is only updated at
+	 * quiescent state transitions: remounting read-only and clean
+	 * unmount.
+	 */
 	sync_inodes_sb(sb);
 	sync_blockdev(sb->s_bdev);
 	blkdev_issue_flush(sb->s_bdev);
-- 
2.25.1