maple_tree: detect dead nodes in mas_start()

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>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 194963149c2d29bb55301841f2587af823438153..6fcf08dbdbf96a6d0d86a1ce35d58a02f585fd87 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;
                }