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authorDavidlohr Bueso <dave@stgolabs.net>2016-01-20 15:00:42 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-20 17:09:18 -0800
commita460bece027301e079b9e53c5e0f67c8e3eaebc1 (patch)
treec53d99607bbbb604bb48cc44d889459d354acd7f
parenta253f1eee6c471d5418983ca9aa9c756e7db5db9 (diff)
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 <dbueso@suse.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Michel Lespinasse <walken@google.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/rbtree.h2
1 files changed, 1 insertions, 1 deletions
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) \