xfs: confirm dotdot target before replacing it during a repair

xfs_dir_replace trips an assertion if you tell it to change a dirent to
point to an inumber that it already points at.  Look up the dotdot entry
directly to confirm that we need to make a change.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

Author: Darrick J. Wong

fs/xfs/scrub/dir_repair.c

@@ -1638,6 +1638,7 @@ xrep_dir_swap(
 	struct xrep_dir		*rd)
 {
 	struct xfs_scrub	*sc = rd->sc;
+	xfs_ino_t		ino;
 	bool			ip_local, temp_local;
 	int			error = 0;
 
@@ -1655,14 +1656,17 @@ xrep_dir_swap(
 
 	/*
 	 * Reset the temporary directory's '..' entry to point to the parent
-	 * that we found.  The temporary directory was created with the root
-	 * directory as the parent, so we can skip this if repairing a
-	 * subdirectory of the root.
+	 * that we found.  The dirent replace code asserts if the dirent
+	 * already points at the new inumber, so we look it up here.
 	 *
 	 * It's also possible that this replacement could also expand a sf
 	 * tempdir into block format.
 	 */
-	if (rd->pscan.parent_ino != sc->mp->m_rootip->i_ino) {
+	error = xchk_dir_lookup(sc, rd->sc->tempip, &xfs_name_dotdot, &ino);
+	if (error)
+		return error;
+
+	if (rd->pscan.parent_ino != ino) {
 		error = xrep_dir_replace(rd, rd->sc->tempip, &xfs_name_dotdot,
 				rd->pscan.parent_ino, rd->tx.req.resblks);
 		if (error)