xfs: don't check for AG deadlock for realtime files in bunmapi

Commit 5b094d6d ("xfs: fix multi-AG deadlock in xfs_bunmapi") added
a check in __xfs_bunmapi() to stop early if we would touch multiple AGs
in the wrong order. However, this check isn't applicable for realtime
files. In most cases, it just makes us do unnecessary commits. However,
without the fix from the previous commit ("xfs: fix realtime file data
space leak"), if the last and second-to-last extents also happen to have
different "AG numbers", then the break actually causes __xfs_bunmapi()
to return without making any progress, which sends
xfs_itruncate_extents_flags() into an infinite loop.

Fixes: 5b094d6d ("xfs: fix multi-AG deadlock in xfs_bunmapi")
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_bmap.c

@@ -5404,7 +5404,7 @@ __xfs_bunmapi(
 		 * Make sure we don't touch multiple AGF headers out of order
 		 * in a single transaction, as that could cause AB-BA deadlocks.
 		 */
-		if (!wasdel) {
+		if (!wasdel && !isrt) {
 			agno = XFS_FSB_TO_AGNO(mp, del.br_startblock);
 			if (prev_agno != NULLAGNUMBER && prev_agno > agno)
 				break;