xfs: check that bc_nlevels never overflows

Warn if we ever bump nlevels higher than the allowed maximum cursor
height.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_btree.c

@@ -2933,6 +2933,7 @@ xfs_btree_new_iroot(
 	be16_add_cpu(&block->bb_level, 1);
 	xfs_btree_set_numrecs(block, 1);
 	cur->bc_nlevels++;
+	ASSERT(cur->bc_nlevels <= XFS_BTREE_MAXLEVELS);
 	cur->bc_ptrs[level + 1] = 1;
 
 	kp = xfs_btree_key_addr(cur, 1, block);
@@ -3096,6 +3097,7 @@ xfs_btree_new_root(
 	xfs_btree_setbuf(cur, cur->bc_nlevels, nbp);
 	cur->bc_ptrs[cur->bc_nlevels] = nptr;
 	cur->bc_nlevels++;
+	ASSERT(cur->bc_nlevels <= XFS_BTREE_MAXLEVELS);
 	*stat = 1;
 	return 0;
 error0:

fs/xfs/libxfs/xfs_btree_staging.c

@@ -703,6 +703,7 @@ xfs_btree_bload_compute_geometry(
 			 * block-based btree level.
 			 */
 			cur->bc_nlevels++;
+			ASSERT(cur->bc_nlevels <= XFS_BTREE_MAXLEVELS);
 			xfs_btree_bload_level_geometry(cur, bbl, level,
 					nr_this_level, &avg_per_block,
 					&level_blocks, &dontcare64);
@@ -718,6 +719,7 @@ xfs_btree_bload_compute_geometry(
 
 			/* Otherwise, we need another level of btree. */
 			cur->bc_nlevels++;
+			ASSERT(cur->bc_nlevels <= XFS_BTREE_MAXLEVELS);
 		}
 
 		nr_blocks += level_blocks;