xfs: don't free rt blocks when we're doing a REMAP bunmapi call

When callers pass XFS_BMAPI_REMAP into xfs_bunmapi, they want the extent
to be unmapped from the given file fork without the extent being freed.
We do this for non-rt files, but we forgot to do this for realtime
files.  So far this isn't a big deal since nobody makes a bunmapi call
to a rt file with the REMAP flag set, but don't leave a logic bomb.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -5046,20 +5046,25 @@ xfs_bmap_del_extent_real(
 
 	flags = XFS_ILOG_CORE;
 	if (whichfork == XFS_DATA_FORK && XFS_IS_REALTIME_INODE(ip)) {
-		xfs_fsblock_t	bno;
 		xfs_filblks_t	len;
 		xfs_extlen_t	mod;
 
-		bno = div_u64_rem(del->br_startblock, mp->m_sb.sb_rextsize,
-				  &mod);
-		ASSERT(mod == 0);
 		len = div_u64_rem(del->br_blockcount, mp->m_sb.sb_rextsize,
 				  &mod);
 		ASSERT(mod == 0);
 
-		error = xfs_rtfree_extent(tp, bno, (xfs_extlen_t)len);
-		if (error)
-			goto done;
+		if (!(bflags & XFS_BMAPI_REMAP)) {
+			xfs_fsblock_t	bno;
+
+			bno = div_u64_rem(del->br_startblock,
+					mp->m_sb.sb_rextsize, &mod);
+			ASSERT(mod == 0);
+
+			error = xfs_rtfree_extent(tp, bno, (xfs_extlen_t)len);
+			if (error)
+				goto done;
+		}
+
 		do_fx = 0;
 		nblks = len * mp->m_sb.sb_rextsize;
 		qfield = XFS_TRANS_DQ_RTBCOUNT;