From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH tip/core/rcu 12/14] bonding/bond_alb.c: Apply ACCESS_ONCE() to avoid sparse false positive Date: Fri, 15 Nov 2013 16:40:15 -0800 Message-ID: <1384562417-817-12-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 e31.co.us.ibm.com ([32.97.110.149]:53635 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754849Ab3KPAk2 (ORCPT ); Fri, 15 Nov 2013 19:40:28 -0500 Received: from /spool/local by e31.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 15 Nov 2013 17:40:28 -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 bond_alb_handle_active_change() 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 --- drivers/net/bonding/bond_alb.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c index 91f179d5135c..67d3b2893aa3 100644 --- a/drivers/net/bonding/bond_alb.c +++ b/drivers/net/bonding/bond_alb.c @@ -1667,7 +1667,8 @@ void bond_alb_handle_active_change(struct bonding *bond, struct slave *new_slave } swap_slave = bond->curr_active_slave; - rcu_assign_pointer(bond->curr_active_slave, new_slave); + /* Both --rcu and visible, so ACCESS_ONCE() is OK. */ + ACCESS_ONCE(bond->curr_active_slave) = new_slave; if (!new_slave || list_empty(&bond->slave_list)) return; -- 1.8.1.5