xfs: error out if trying to add attrs and anextents > 0

We shouldn't assert if somehow we end up trying to add an attr fork to
an inode that apparently already has attr extents because this is an
indication of on-disk corruption.  Instead, return an error code to
userspace.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -1153,6 +1153,10 @@ xfs_bmap_add_attrfork(
 		goto trans_cancel;
 	if (XFS_IFORK_Q(ip))
 		goto trans_cancel;
+	if (ip->i_d.di_anextents != 0) {
+		error = -EFSCORRUPTED;
+		goto trans_cancel;
+	}
 	if (ip->i_d.di_aformat != XFS_DINODE_FMT_EXTENTS) {
 		/*
 		 * For inodes coming from pre-6.2 filesystems.
@@ -1160,7 +1164,6 @@ xfs_bmap_add_attrfork(
 		ASSERT(ip->i_d.di_aformat == 0);
 		ip->i_d.di_aformat = XFS_DINODE_FMT_EXTENTS;
 	}
-	ASSERT(ip->i_d.di_anextents == 0);
 
 	xfs_trans_ijoin(tp, ip, 0);
 	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);