[6/8] maple_tree: add smp_rmb() to dead node detection

Commit Message

Liam R. Howlett March 27, 2023, 6:55 p.m. UTC

From: "Liam R. Howlett" <[e-mail]>

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/[e-mail]
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Cc: [e-mail]
Signed-off-by: Liam R. Howlett <[e-mail]>
---
 lib/maple_tree.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Patch

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 6b6eddadd9d2..8ad2d1669fad 100644
--- 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);
 }