From a460bece027301e079b9e53c5e0f67c8e3eaebc1 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Wed, 20 Jan 2016 15:00:42 -0800 Subject: [PATCH] rbtree: use READ_ONCE in RB_EMPTY_ROOT With commit 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 Acked-by: Peter Zijlstra (Intel) Cc: Michel Lespinasse Cc: Rusty Russell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 a5aa7ae671f4..b6900099ea81 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) \ -- 2.20.1