于 2013/11/16 8:40, Paul E. McKenney 写道:
> From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>
> 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.
I think it is fit for net-next.
> Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> ---
> 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
