From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH tip/core/rcu 10/14] bridge/br_mdb: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 15 Nov 2013 16:40:13 -0800 Message-ID: <1384562417-817-10-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: Stephen Hemminger , tglx@linutronix.de, laijs@cn.fujitsu.com, edumazet@google.com, peterz@infradead.org, fweisbec@gmail.com, bridge@lists.linux-foundation.org, josh@joshtriplett.org, rostedt@goodmis.org, "David S. Miller" , dhowells@redhat.com, sbw@mit.edu, niv@us.ibm.com, netdev@vger.kernel.org, mathieu.desnoyers@efficios.com, dipankar@in.ibm.com, darren@dvhart.com, akpm@linux-foundation.org, "Paul E. McKenney" , mingo@kernel.org To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1384562417-817-1-git-send-email-paulmck@linux.vnet.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: bridge-bounces@lists.linux-foundation.org Errors-To: bridge-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org 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 __br_mdb_del() is 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_mdb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/bridge/br_mdb.c b/net/bridge/br_mdb.c index 85a09bb5ca51..de7197ba8695 100644 --- a/net/bridge/br_mdb.c +++ b/net/bridge/br_mdb.c @@ -447,7 +447,7 @@ static int __br_mdb_del(struct net_bridge *br, struct br_mdb_entry *entry) if (p->port->state == BR_STATE_DISABLED) goto unlock; - 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); -- 1.8.1.5