udf_rename(): only access the child content on cross-directory rename

We can't really afford locking the source on same-directory rename;
currently vfs_rename() tries to do that, but it will have to be
changed.  The logics in udf_rename() is lazy and goes looking for
".." in source even in same-directory case.  It's not hard to get
rid of that, leaving that behaviour only for cross-directory case;
that VFS can get locks safely (and will keep doing that after the
coming changes).
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/udf/namei.c

@@ -766,7 +766,7 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	struct inode *old_inode = d_inode(old_dentry);
 	struct inode *new_inode = d_inode(new_dentry);
 	struct udf_fileident_iter oiter, niter, diriter;
-	bool has_diriter = false;
+	bool has_diriter = false, is_dir = false;
 	int retval;
 	struct kernel_lb_addr tloc;
 
@@ -789,6 +789,9 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 			if (!empty_dir(new_inode))
 				goto out_oiter;
 		}
+		is_dir = true;
+	}
+	if (is_dir && old_dir != new_dir) {
 		retval = udf_fiiter_find_entry(old_inode, &dotdot_name,
 					       &diriter);
 		if (retval == -ENOENT) {
@@ -878,7 +881,9 @@ static int udf_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 			       udf_dir_entry_len(&diriter.fi));
 		udf_fiiter_write_fi(&diriter, NULL);
 		udf_fiiter_release(&diriter);
+	}
 
+	if (is_dir) {
 		inode_dec_link_count(old_dir);
 		if (new_inode)
 			inode_dec_link_count(new_inode);