From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH tip/core/rcu 03/14] bridge: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 15 Nov 2013 16:40:06 -0800 Message-ID: <1384562417-817-3-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" , Stephen Hemminger , "David S. Miller" , bridge@lists.linux-foundation.org, netdev@vger.kernel.org To: linux-kernel@vger.kernel.org Return-path: Received: from e32.co.us.ibm.com ([32.97.110.150]:41080 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754840Ab3KPAk1 (ORCPT ); Fri, 15 Nov 2013 19:40:27 -0500 Received: from /spool/local by e32.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 uses in br_multicast_del_pg() and br_multicast_new_port_group() are legitimate: They are 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 these false positives by laundering the pointers using ACCESS_ONCE() as suggested by Eric Dumazet and Josh Triplett. Reported-by: kbuild test robot Signed-off-by: Paul E. McKenney Cc: Stephen Hemminger Cc: "David S. Miller" Cc: bridge@lists.linux-foundation.org Cc: netdev@vger.kernel.org --- net/bridge/br_multicast.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index d1c578630678..bcc4bbc16498 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -267,7 +267,7 @@ static void br_multicast_del_pg(struct net_bridge *br, if (p != pg) continue; - rcu_assign_pointer(*pp, p->next); + ACCESS_ONCE(*pp) = p->next; /* OK: Both --rcu and visible. */ hlist_del_init(&p->mglist); del_timer(&p->timer); call_rcu_bh(&p->rcu, br_multicast_free_pg); @@ -646,7 +646,7 @@ struct net_bridge_port_group *br_multicast_new_port_group( p->addr = *group; p->port = port; p->state = state; - rcu_assign_pointer(p->next, next); + ACCESS_ONCE(p->next) = next; /* OK: Both --rcu and visible. */ hlist_add_head(&p->mglist, &port->mglist); setup_timer(&p->timer, br_multicast_port_group_expired, (unsigned long)p); -- 1.8.1.5