ovl: fix getcwd() failure after unsuccessful rmdir

ovl_remove_upper() should do d_drop() only after it successfully
removes the dir, otherwise a subsequent getcwd() system call will
fail, breaking userspace programs.

This is to fix: https://bugzilla.kernel.org/show_bug.cgi?id=110491

Signed-off-by: Rui Wang <rui.y.wang@intel.com>
Reviewed-by: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org>

fs/overlayfs/dir.c

@@ -618,7 +618,8 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
 	 * sole user of this dentry.  Too tricky...  Just unhash for
 	 * now.
 	 */
-	d_drop(dentry);
+	if (!err)
+		d_drop(dentry);
 	inode_unlock(dir);
 
 	return err;