xfs: cleanup fdblock/frextent accounting in xfs_bmap_del_extent_delay

The code to account fdblocks and frextents in xfs_bmap_del_extent_delay
is a bit weird in that it accounts frextents before the iext tree
manipulations and fdblocks after it.  Given that the iext tree
manipulations cannot fail currently that's not really a problem, but
still odd.  Move the frextent manipulation to the end, and use a
fdblocks variable to account of the unconditional indirect blocks and
the data blocks only freed for !RT.  This prepares for following
updates in the area and already makes the code more readable.

Also remove the !isrt assert given that this code clearly handles
rt extents correctly, and we'll soon reinstate delalloc support for
RT inodes.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/libxfs/xfs_bmap.c

@@ -4919,6 +4919,7 @@ xfs_bmap_del_extent_delay(
 	xfs_fileoff_t		del_endoff, got_endoff;
 	xfs_filblks_t		got_indlen, new_indlen, stolen;
 	uint32_t		state = xfs_bmap_fork_to_state(whichfork);
+	uint64_t		fdblocks;
 	int			error = 0;
 	bool			isrt;
 
@@ -4934,15 +4935,11 @@ xfs_bmap_del_extent_delay(
 	ASSERT(got->br_startoff <= del->br_startoff);
 	ASSERT(got_endoff >= del_endoff);
 
-	if (isrt)
-		xfs_add_frextents(mp, xfs_rtb_to_rtx(mp, del->br_blockcount));
-
 	/*
 	 * Update the inode delalloc counter now and wait to update the
 	 * sb counters as we might have to borrow some blocks for the
 	 * indirect block accounting.
 	 */
-	ASSERT(!isrt);
 	error = xfs_quota_unreserve_blkres(ip, del->br_blockcount);
 	if (error)
 		return error;
@@ -5019,12 +5016,15 @@ xfs_bmap_del_extent_delay(
 
 	ASSERT(da_old >= da_new);
 	da_diff = da_old - da_new;
-	if (!isrt)
-		da_diff += del->br_blockcount;
-	if (da_diff) {
-		xfs_add_fdblocks(mp, da_diff);
-		xfs_mod_delalloc(mp, -da_diff);
-	}
+	fdblocks = da_diff;
+
+	if (isrt)
+		xfs_add_frextents(mp, xfs_rtb_to_rtx(mp, del->br_blockcount));
+	else
+		fdblocks += del->br_blockcount;
+
+	xfs_add_fdblocks(mp, fdblocks);
+	xfs_mod_delalloc(mp, -(int64_t)fdblocks);
 	return error;
 }