maple_tree: clear up index and last setting in single entry tree

When there is a single entry tree (range of 0-0 pointing to an entry),
then ensure the limit is either 0-0 or 1-oo, depending on where the user
walks.  Ensure the correct node setting as well; either MAS_ROOT or
MAS_NONE.

Link: https://lkml.kernel.org/r/20230518145544.1722059-33-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -5023,24 +5023,25 @@ void *mas_walk(struct ma_state *mas)
 {
 	void *entry;
 
+	if (mas_is_none(mas) || mas_is_paused(mas) || mas_is_ptr(mas))
+		mas->node = MAS_START;
 retry:
 	entry = mas_state_walk(mas);
-	if (mas_is_start(mas))
+	if (mas_is_start(mas)) {
 		goto retry;
-
-	if (mas_is_ptr(mas)) {
+	} else if (mas_is_none(mas)) {
+		mas->index = 0;
+		mas->last = ULONG_MAX;
+	} else if (mas_is_ptr(mas)) {
 		if (!mas->index) {
 			mas->last = 0;
-		} else {
-			mas->index = 1;
-			mas->last = ULONG_MAX;
+			return entry;
 		}
-		return entry;
-	}
 
-	if (mas_is_none(mas)) {
-		mas->index = 0;
+		mas->index = 1;
 		mas->last = ULONG_MAX;
+		mas->node = MAS_NONE;
+		return NULL;
 	}
 
 	return entry;