maple_tree: add a test check deficient node

Add a test to assert when resulting a deficient node on splitting.

We can achieve this by build a tree with two nodes. With the left
node with consecutive data from 0 and leave some room for the final
insert to locate in left node. And the right node a full node to force
the split happens on the left node.

Link: https://lkml.kernel.org/r/20241113031616.10530-3-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/test_maple_tree.c

@@ -1563,6 +1563,30 @@ static noinline void __init check_root_expand(struct maple_tree *mt)
 	mas_unlock(&mas);
 }
 
+static noinline void __init check_deficient_node(struct maple_tree *mt)
+{
+	MA_STATE(mas, mt, 0, 0);
+	int count;
+
+	mas_lock(&mas);
+	for (count = 0; count < 10; count++) {
+		mas_set(&mas, count);
+		mas_store_gfp(&mas, xa_mk_value(count), GFP_KERNEL);
+	}
+
+	for (count = 20; count < 39; count++) {
+		mas_set(&mas, count);
+		mas_store_gfp(&mas, xa_mk_value(count), GFP_KERNEL);
+	}
+
+	for (count = 10; count < 12; count++) {
+		mas_set(&mas, count);
+		mas_store_gfp(&mas, xa_mk_value(count), GFP_KERNEL);
+	}
+	mas_unlock(&mas);
+	mt_validate(mt);
+}
+
 static noinline void __init check_gap_combining(struct maple_tree *mt)
 {
 	struct maple_enode *mn1, *mn2;
@@ -3796,6 +3820,10 @@ static int __init maple_tree_seed(void)
 	goto skip;
 #endif
 
+	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
+	check_deficient_node(&tree);
+	mtree_destroy(&tree);
+
 	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
 	check_store_null(&tree);
 	mtree_destroy(&tree);