xfs: try to idiot-proof the allocators

Source kernel commit: 6de4b1ab470fe52351415217ac6dffddee571c45

In porting his development branch to 6.3-rc1, yours truly has
repeatedly screwed up the args->pag being fed to the xfs_alloc_vextent*
functions.  Add some debugging assertions to test the preconditions
required of the callers.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
diff --git a/libxfs/xfs_alloc.c b/libxfs/xfs_alloc.c
index 645c73f..1e3079a 100644
--- a/libxfs/xfs_alloc.c
+++ b/libxfs/xfs_alloc.c
@@ -3275,6 +3275,9 @@
 	xfs_agnumber_t		minimum_agno;
 	int			error;
 
+	ASSERT(args->pag != NULL);
+	ASSERT(args->pag->pag_agno == agno);
+
 	args->agno = agno;
 	args->agbno = 0;
 	error = xfs_alloc_vextent_check_args(args, XFS_AGB_TO_FSB(mp, agno, 0),
@@ -3390,6 +3393,8 @@
 	bool			bump_rotor = false;
 	int			error;
 
+	ASSERT(args->pag == NULL);
+
 	args->agno = NULLAGNUMBER;
 	args->agbno = NULLAGBLOCK;
 	error = xfs_alloc_vextent_check_args(args, target, &minimum_agno);
@@ -3438,6 +3443,8 @@
 	xfs_agnumber_t		start_agno;
 	int			error;
 
+	ASSERT(args->pag == NULL);
+
 	args->agno = NULLAGNUMBER;
 	args->agbno = NULLAGBLOCK;
 	error = xfs_alloc_vextent_check_args(args, target, &minimum_agno);
@@ -3466,6 +3473,9 @@
 	xfs_agnumber_t		minimum_agno;
 	int			error;
 
+	ASSERT(args->pag != NULL);
+	ASSERT(args->pag->pag_agno == XFS_FSB_TO_AGNO(mp, target));
+
 	args->agno = XFS_FSB_TO_AGNO(mp, target);
 	args->agbno = XFS_FSB_TO_AGBNO(mp, target);
 	error = xfs_alloc_vextent_check_args(args, target, &minimum_agno);
@@ -3498,6 +3508,9 @@
 	bool			needs_perag = args->pag == NULL;
 	int			error;
 
+	if (!needs_perag)
+		ASSERT(args->pag->pag_agno == XFS_FSB_TO_AGNO(mp, target));
+
 	args->agno = XFS_FSB_TO_AGNO(mp, target);
 	args->agbno = XFS_FSB_TO_AGBNO(mp, target);
 	error = xfs_alloc_vextent_check_args(args, target, &minimum_agno);