From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH tip/core/rcu 06/14] ipv6/ip6_tunnel: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 15 Nov 2013 16:40:09 -0800 Message-ID: <1384562417-817-6-git-send-email-paulmck@linux.vnet.ibm.com> References: <20131116003946.GA316@linux.vnet.ibm.com> <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com> Cc: 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, "Paul E. McKenney" , "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , netdev@vger.kernel.org To: linux-kernel@vger.kernel.org Return-path: Received: from e38.co.us.ibm.com ([32.97.110.159]:38301 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754836Ab3KPAk1 (ORCPT ); Fri, 15 Nov 2013 19:40:27 -0500 Received: from /spool/local by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 15 Nov 2013 17:40:26 -0700 In-Reply-To: <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: From: "Paul E. McKenney" The sparse checking for rcu_assign_pointer() was recently upgraded to reject non-__kernel address spaces. This also rejects __rcu, which is almost always the right thing to do. However, the use in ip6_tnl_unlink() is legitimate: It is assigning a pointer to an element from an RCU-protected list, and all elements of this list are already visible to caller. This commit therefore silences this false positive by laundering the pointer using ACCESS_ONCE() as suggested by Eric Dumazet and Josh Triplett. Reported-by: kbuild test robot Signed-off-by: Paul E. McKenney Cc: "David S. Miller" Cc: Alexey Kuznetsov Cc: James Morris Cc: Hideaki YOSHIFUJI Cc: Patrick McHardy Cc: netdev@vger.kernel.org --- net/ipv6/ip6_tunnel.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c index 61355f7f4da5..2bea7a4e49ed 100644 --- a/net/ipv6/ip6_tunnel.c +++ b/net/ipv6/ip6_tunnel.c @@ -245,7 +245,8 @@ ip6_tnl_unlink(struct ip6_tnl_net *ip6n, struct ip6_tnl *t) (iter = rtnl_dereference(*tp)) != NULL; tp = &iter->next) { if (t == iter) { - rcu_assign_pointer(*tp, t->next); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(*tp) = t->next; break; } } -- 1.8.1.5