maple_tree: add regression test for spanning store bug

Add a regression test to assert that, when performing a spanning store
which consumes the entirety of the rightmost right leaf node does not
result in maple tree corruption when doing so.

This achieves this by building a test tree of 3 levels and establishing a
store which ultimately results in a spanned store of this nature.

Link: https://lkml.kernel.org/r/30cdc10[e-mail]
Signed-off-by: Lorenzo Stoakes <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Reviewed-by: Liam R. Howlett <[e-mail]>
Reviewed-by: Wei Yang <[e-mail]>
Cc: Bert Karwatzki <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Mikhail Gavrilov <[e-mail]>
Cc: Sidhartha Kumar <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/radix-tree/maple.c

···
 	check_nomem(&tree);
 }
 
+static unsigned long get_last_index(struct ma_state *mas)
+{
+	struct maple_node *node = mas_mn(mas);
+	enum maple_type mt = mte_node_type(mas->node);
+	unsigned long *pivots = ma_pivots(node, mt);
+	unsigned long last_index = mas_data_end(mas);
+
+	BUG_ON(last_index == 0);
+
+	return pivots[last_index - 1] + 1;
+}
+
+/*
+ * Assert that we handle spanning stores that consume the entirety of the right
+ * leaf node correctly.
+ */
+static void test_spanning_store_regression(void)
+{
+	unsigned long from = 0, to = 0;
+	DEFINE_MTREE(tree);
+	MA_STATE(mas, &tree, 0, 0);
+
+	/*
+	 * Build a 3-level tree. We require a parent node below the root node
+	 * and 2 leaf nodes under it, so we can span the entirety of the right
+	 * hand node.
+	 */
+	build_full_tree(&tree, 0, 3);
+
+	/* Descend into position at depth 2. */
+	mas_reset(&mas);
+	mas_start(&mas);
+	mas_descend(&mas);
+	mas_descend(&mas);
+
+	/*
+	 * We need to establish a tree like the below.
+	 *
+	 * Then we can try a store in [from, to] which results in a spanned
+	 * store across nodes B and C, with the maple state at the time of the
+	 * write being such that only the subtree at A and below is considered.
+	 *
+	 * Height
+	 *  0                              Root Node
+	 *                                  /      \
+	 *                    pivot = to   /        \ pivot = ULONG_MAX
+	 *                                /          \
+	 *   1                       A [-----]       ...
+	 *                              /   \
+	 *                pivot = from /     \ pivot = to
+	 *                            /       \
+	 *   2 (LEAVES)          B [-----]  [-----] C
+	 *                                       ^--- Last pivot to.
+	 */
+	while (true) {
+		unsigned long tmp = get_last_index(&mas);
+
+		if (mas_next_sibling(&mas)) {
+			from = tmp;
+			to = mas.max;
+		} else {
+			break;
+		}
+	}
+
+	BUG_ON(from == 0 && to == 0);
+
+	/* Perform the store. */
+	mas_set_range(&mas, from, to);
+	mas_store_gfp(&mas, xa_mk_value(0xdead), GFP_KERNEL);
+
+	/* If the regression occurs, the validation will fail. */
+	mt_validate(&tree);
+
+	/* Cleanup. */
+	__mt_destroy(&tree);
+}
+
+static void regression_tests(void)
+{
+	test_spanning_store_regression();
+}
+
 void maple_tree_tests(void)
 {
 #if !defined(BENCH)
+	regression_tests();
 	farmer_tests();
 #endif
 	maple_tree_seed();