From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH tip/core/rcu 11/14] bonding/bond_main: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 15 Nov 2013 16:40:14 -0800 Message-ID: <1384562417-817-11-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 uses in bond_change_active_slave() and __bond_release_one() are legitimate: They are assigning a pointer to an element from an RCU-protected list (or a NULL pointer), and all elements of this list are already visible to caller. This commit therefore silences these false positives either by laundering the pointers using ACCESS_ONCE() as suggested by Eric Dumazet and Josh Triplett, or by using RCU_INIT_POINTER() for NULL pointer assignments. 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 --- drivers/net/bonding/bond_main.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index 72df399c4ab3..bbd7fd3e46fe 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -890,7 +890,8 @@ void bond_change_active_slave(struct bonding *bond, struct slave *new_active) if (new_active) bond_set_slave_active_flags(new_active); } else { - rcu_assign_pointer(bond->curr_active_slave, new_active); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(bond->curr_active_slave) = new_active; } if (bond->params.mode == BOND_MODE_ACTIVEBACKUP) { @@ -1801,7 +1802,7 @@ static int __bond_release_one(struct net_device *bond_dev, } if (all) { - rcu_assign_pointer(bond->curr_active_slave, NULL); + RCU_INIT_POINTER(bond->curr_active_slave, NULL); } else if (oldcurrent == slave) { /* * Note that we hold RTNL over this sequence, so there -- 1.8.1.5