maple_tree: add smp_rmb() to dead node detection

Add an smp_rmb() before reading the parent pointer to ensure that anything
read from the node prior to the parent pointer hasn't been reordered ahead
of this check.

The is necessary for RCU mode.

Link: https://lkml.kernel.org/r/20230227173632.3292573-7-surenb@google.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Cc: stable@vger.kernel.org
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 6b6eddadd9d2a58b6cc96fbc7ba02ed7fcd08568..8ad2d1669fadf18005208f4f89a13adccd927763 100644 (file)
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -539,9 +539,11 @@ static inline struct maple_node *mte_parent(const struct maple_enode *enode)
  */
 static inline bool ma_dead_node(const struct maple_node *node)
 {
-       struct maple_node *parent = (void *)((unsigned long)
-                                            node->parent & ~MAPLE_NODE_MASK);
+       struct maple_node *parent;
 
+       /* Do not reorder reads from the node prior to the parent check */
+       smp_rmb();
+       parent = (void *)((unsigned long) node->parent & ~MAPLE_NODE_MASK);
        return (parent == node);
 }
 
@@ -556,6 +558,8 @@ static inline bool mte_dead_node(const struct maple_enode *enode)
        struct maple_node *parent, *node;
 
        node = mte_to_node(enode);
+       /* Do not reorder reads from the node prior to the parent check */
+       smp_rmb();
        parent = mte_parent(enode);
        return (parent == node);
 }