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 R. Howlett <Liam.Howlett@oracle.com>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index cc356b8369adbda99c505929a17fe43b55b08664..089cd76ec37941f5548cde57a9a926e7a51fabcc 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1360,12 +1360,16 @@ 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;
                }