Hi, Alex

Thanks for your reply.

I checked all the nic driver in driver/net/ethernet/intel. And I found that
only here the rtnl_lock is used.
So I am curios why rtnl_lock is used when waking up the tupper device tx
queue here. And the rtnl_lock is not used in other places.

Best Regards!
Zhu Yanjun

On Mon, Jun 6, 2016 at 2:40 AM, Alexander Duyck <alexander.duyck@gmail.com>
wrote:

> On Sun, Jun 5, 2016 at 2:14 AM,  <zyjzyj2000@gmail.com> wrote:
> > From: Zhu Yanjun <zyjzyj2000@gmail.com>
> >
> >
> > Signed-off-by: Zhu Yanjun <zyjzyj2000@gmail.com>
> > ---
> >  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > index 088c47c..cb19cbc 100644
> > --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > @@ -6840,7 +6840,7 @@ static void ixgbe_watchdog_link_is_up(struct
> ixgbe_adapter *adapter)
> >         netif_tx_wake_all_queues(adapter->netdev);
> >
> >         /* enable any upper devices */
> > -       rtnl_lock();
> > +       rcu_read_lock();
> >         netdev_for_each_all_upper_dev_rcu(adapter->netdev, upper, iter) {
> >                 if (netif_is_macvlan(upper)) {
> >                         struct macvlan_dev *vlan = netdev_priv(upper);
> > @@ -6849,7 +6849,7 @@ static void ixgbe_watchdog_link_is_up(struct
> ixgbe_adapter *adapter)
> >                                 netif_tx_wake_all_queues(upper);
> >                 }
> >         }
> > -       rtnl_unlock();
> > +       rcu_read_unlock();
> >
> >         /* update the default user priority for VFs */
> >         ixgbe_update_default_up(adapter);
>
> The rtnl_lock is being used to prevent any changes to the upper
> devices while the interface is going through and updating the Tx queue
> configuration on them.  Without that lock you introduce possible bugs
> since you could have queues freed or added while this loop is in the
> middle of trying to update the state of it.
>
> As a general rule you use rcu_read_lock when you are only reading an
> RCU protected structure, you use rtnl_lock when you have to protect
> the system from any other changes while you are updating network
> configuration.  In this case netif_tx_wake_all_queues changes the
> state of the upper device.  The use of rtnl_lock here is intentional
> and it is best to just leave it as is unless you have some actual bug
> you are seeing.
>
> - Alex
>