Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756157Ab3JIWK1 (ORCPT ); Wed, 9 Oct 2013 18:10:27 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:41157 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752463Ab3JIWK0 (ORCPT ); Wed, 9 Oct 2013 18:10:26 -0400 Message-ID: <1381356624.4971.26.camel@edumazet-glaptop.roam.corp.google.com> Subject: Re: [PATCH v2 tip/core/rcu 07/13] ipv6/ip6_tunnel: Apply rcu_access_pointer() to avoid sparse false positive From: Eric Dumazet To: paulmck@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , netdev@vger.kernel.org Date: Wed, 09 Oct 2013 15:10:24 -0700 In-Reply-To: <20131009215747.GA5790@linux.vnet.ibm.com> References: <20131009212920.GA15413@linux.vnet.ibm.com> <1381354186-16285-1-git-send-email-paulmck@linux.vnet.ibm.com> <1381354186-16285-7-git-send-email-paulmck@linux.vnet.ibm.com> <1381354949.4971.20.camel@edumazet-glaptop.roam.corp.google.com> <20131009215747.GA5790@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 820 Lines: 27 On Wed, 2013-10-09 at 14:57 -0700, Paul E. McKenney wrote: > Hmmm... I could use RCU_INIT_POINTER(). Something like the following? > > RCU_INIT_POINTER(ACCESS_ONCE(*tp), t->next); > > The ACCESS_ONCE() to prevent the compiler from doing anything stupid. > Presumably the value of t->next cannot change, so a normal load suffices. > > Or did you have something else in mind? Well, *tp and t->next are both of the same type, with __rcu attribute. struct ip6_tnl __rcu **tp; So I meant : ACCESS_ONCE(*tp) = t->next; If really we can have a really stupid compiler. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/