[PATCH 2/2] maple_tree: assert retrieving new value on a tree containing just a leaf node

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

From: Wei Yang <richard.weiyang@gmail.com>

Original code may not get the new value after overwriting the whole
range on a maple tree containing just a leaf node. The reason is we didn't
set the only root node dead during destroy.

Add a test case to ensure the new value is returned when overwriting a
tree containing just a leaf node.

Link: https://lore.kernel.org/all/20250407231354.11771-1-richard.weiyang@gmail.com/
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Liam R. Howlett <Liam.Howlett@Oracle.com>
[Liam.Howlett@oracle.com: Use mtree_destroy, mas_set, and set val]
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 tools/testing/radix-tree/maple.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
index 172700fb7784d..2f6dcdc7a38f6 100644
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -35257,6 +35257,32 @@ static noinline void __init check_rcu_simulated(struct maple_tree *mt)
 	MT_BUG_ON(mt, mas_prev(&mas_reader, 0) != xa_mk_value(val));
 	rcu_read_unlock();
 
+	/* Clear out tree & create one with only root node */
+	mtree_destroy(mt);
+	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE | MT_FLAGS_USE_RCU);
+	mas_pause(&mas_writer);
+	mas_lock(&mas_writer);
+	for (i = 0; i <= 5; i++) {
+		mas_writer.index = i * 10;
+		mas_writer.last = i * 10 + 5;
+		mas_store_gfp(&mas_writer, xa_mk_value(i), GFP_KERNEL);
+	}
+	mas_unlock(&mas_writer);
+	target = 10;
+	val = 20;
+	mas_set(&mas_reader, target);
+	rcu_read_lock();
+	MT_BUG_ON(mt, mas_walk(&mas_reader) != xa_mk_value(target/10));
+	MT_BUG_ON(mt, mte_is_leaf(mas_reader.node) != true);
+
+	/* Overwrite the whole range */
+	mas_lock(&mas_writer);
+	mas_set_range(&mas_writer, 0, ULONG_MAX);
+	mas_store_gfp(&mas_writer, xa_mk_value(val), GFP_KERNEL);
+	mas_unlock(&mas_writer);
+	MT_BUG_ON(mt, mas_walk(&mas_reader) != xa_mk_value(val));
+	rcu_read_unlock();
+
 	rcu_unregister_thread();
 }
 
-- 
2.47.2