maple_tree: detect dead nodes in mas_start()

commit a7b92d59c885018cb7bb88539892278e4fd64b29 upstream.

When initially starting a search, the root node may already be in the
process of being replaced in RCU mode.  Detect and restart the walk if
this is the case.  This is necessary for RCU mode of the maple tree.

Link: https://lkml.kernel.org/r/20230227173632.3292573-3-surenb@google.com
Cc: <Stable@vger.kernel.org>
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 54484bd756e53ca533656015c27f540f8aa82e05..6b451a432738a97ab0c24a354fc637fe23b650be 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1352,12 +1352,16 @@ static inline struct maple_enode *mas_start(struct ma_state *mas)
                mas->max = ULONG_MAX;
                mas->depth = 0;
 
+retry:
                root = mas_root(mas);
                /* Tree with nodes */
                if (likely(xa_is_node(root))) {
                        mas->depth = 1;
                        mas->node = mte_safe_root(root);
                        mas->offset = 0;
+                       if (mte_dead_node(mas->node))
+                               goto retry;
+
                        return NULL;
                }