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
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 095b9cb1f4f1133efcf6746a689d06d727f05cac..3d53339656e1dd524755f02971f7f86f3552a544 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;
                }