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Subject[PATCH] rbtree: use READ_ONCE in RB_EMPTY_ROOT
Date
With d72da4a4d97 (rbtree: Make lockless searches non-fatal) our rbtrees
provide weak guarantees that allows us to do lockless (and very speculative)
reads of the tree. Such readers cannot see partial stores on nodes, ie
left/right as well as root. As such, similar to the WRITE_ONCE semantics when
doing rotations, use READ_ONCE when checking the root node in RB_EMPTY_ROOT.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
include/linux/rbtree.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index a5aa7ae..b690009 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -50,7 +50,7 @@ struct rb_root {
#define RB_ROOT (struct rb_root) { NULL, }
#define rb_entry(ptr, type, member) container_of(ptr, type, member)

-#define RB_EMPTY_ROOT(root) ((root)->rb_node == NULL)
+#define RB_EMPTY_ROOT(root) (READ_ONCE((root)->rb_node) == NULL)

/* 'empty' nodes are nodes that are known not to be inserted in an rbtree */
#define RB_EMPTY_NODE(node) \
--
2.1.4
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