From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761151AbcAKSXH (ORCPT ); Mon, 11 Jan 2016 13:23:07 -0500 Received: from smtp2.provo.novell.com ([137.65.250.81]:37659 "EHLO smtp2.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759965AbcAKSXF (ORCPT ); Mon, 11 Jan 2016 13:23:05 -0500 From: Davidlohr Bueso To: Andrew Morton , Peter Zijlstra Cc: dave@stgolabs.net, linux-kernel@vger.kernel.org, Davidlohr Bueso Subject: [PATCH] rbtree: use READ_ONCE in RB_EMPTY_ROOT Date: Mon, 11 Jan 2016 10:22:43 -0800 Message-Id: <1452536563-1762-1-git-send-email-dave@stgolabs.net> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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 a5aa7ae..b690009 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) \ -- 2.1.4