test_maple_tree: test modifications while iterating

Add a testcase to ensure the iterator detects bad states on modifications
and does what the user expects

Link: https://lkml.kernel.org/r/20230120162650.984577-5-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/test_maple_tree.c

@@ -1709,6 +1709,74 @@ static noinline void check_forking(struct maple_tree *mt)
 	mtree_destroy(&newmt);
 }
 
+static noinline void check_iteration(struct maple_tree *mt)
+{
+	int i, nr_entries = 125;
+	void *val;
+	MA_STATE(mas, mt, 0, 0);
+
+	for (i = 0; i <= nr_entries; i++)
+		mtree_store_range(mt, i * 10, i * 10 + 9,
+				  xa_mk_value(i), GFP_KERNEL);
+
+	mt_set_non_kernel(99999);
+
+	i = 0;
+	mas_lock(&mas);
+	mas_for_each(&mas, val, 925) {
+		MT_BUG_ON(mt, mas.index != i * 10);
+		MT_BUG_ON(mt, mas.last != i * 10 + 9);
+		/* Overwrite end of entry 92 */
+		if (i == 92) {
+			mas.index = 925;
+			mas.last = 929;
+			mas_store(&mas, val);
+		}
+		i++;
+	}
+	/* Ensure mas_find() gets the next value */
+	val = mas_find(&mas, ULONG_MAX);
+	MT_BUG_ON(mt, val != xa_mk_value(i));
+
+	mas_set(&mas, 0);
+	i = 0;
+	mas_for_each(&mas, val, 785) {
+		MT_BUG_ON(mt, mas.index != i * 10);
+		MT_BUG_ON(mt, mas.last != i * 10 + 9);
+		/* Overwrite start of entry 78 */
+		if (i == 78) {
+			mas.index = 780;
+			mas.last = 785;
+			mas_store(&mas, val);
+		} else {
+			i++;
+		}
+	}
+	val = mas_find(&mas, ULONG_MAX);
+	MT_BUG_ON(mt, val != xa_mk_value(i));
+
+	mas_set(&mas, 0);
+	i = 0;
+	mas_for_each(&mas, val, 765) {
+		MT_BUG_ON(mt, mas.index != i * 10);
+		MT_BUG_ON(mt, mas.last != i * 10 + 9);
+		/* Overwrite end of entry 76 and advance to the end */
+		if (i == 76) {
+			mas.index = 760;
+			mas.last = 765;
+			mas_store(&mas, val);
+			mas_next(&mas, ULONG_MAX);
+		}
+		i++;
+	}
+	/* Make sure the next find returns the one after 765, 766-769 */
+	val = mas_find(&mas, ULONG_MAX);
+	MT_BUG_ON(mt, val != xa_mk_value(76));
+	mas_unlock(&mas);
+	mas_destroy(&mas);
+	mt_set_non_kernel(0);
+}
+
 static noinline void check_mas_store_gfp(struct maple_tree *mt)
 {
 
@@ -2659,6 +2727,10 @@ static int maple_tree_seed(void)
 	goto skip;
 #endif
 
+	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
+	check_iteration(&tree);
+	mtree_destroy(&tree);
+
 	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
 	check_forking(&tree);
 	mtree_destroy(&tree);