The patch titled
Subject: rbtree: use READ_ONCE in RB_EMPTY_ROOT
has been added to the -mm tree. Its filename is
rbtree-use-read_once-in-rb_empty_root.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/rbtree-use-read_once-in-rb_empty_root.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/rbtree-use-read_once-in-rb_empty_root.patch
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From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Subject: rbtree: use READ_ONCE in RB_EMPTY_ROOT
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@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/rbtree.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN include/linux/rbtree.h~rbtree-use-read_once-in-rb_empty_root include/linux/rbtree.h
--- a/include/linux/rbtree.h~rbtree-use-read_once-in-rb_empty_root
+++ a/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) \
_
Patches currently in -mm which might be from dave@xxxxxxxxxxxx are
rbtree-use-read_once-in-rb_empty_root.patch
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