Commit a460bece authored Jan 20, 2016 by Davidlohr Bueso Committed by Linus Torvalds Jan 20, 2016

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: 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>

parent a253f1ee

include/linux/rbtree.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -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) \