Commit a460bece authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds

rbtree: use READ_ONCE in RB_EMPTY_ROOT

With commit d72da4a4 ("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: default avatarDavidlohr Bueso <>
Acked-by: default avatarPeter Zijlstra (Intel) <>
Cc: Michel Lespinasse <>
Cc: Rusty Russell <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent a253f1ee
......@@ -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) \
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