Messages in this thread Patch in this message | | | 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 |
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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 <fengguang.wu@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: "David S. Miller" <davem@davemloft.net> 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
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