Re: [PATCH net] net: dsa: link interfaces with the DSA master to get rid of lockdep warnings

[Jakub Kicinski]

On Mon, 13 Jul 2020 19:24:43 +0300 Vladimir Oltean wrote:
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 743caabeaaa6..a951b2a7d79a 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -1994,6 +1994,13 @@ int dsa_slave_create(struct dsa_port *port)
>                          ret, slave_dev->name);
>               goto out_phy;
>       }
> +     rtnl_lock();
> +     ret = netdev_upper_dev_link(master, slave_dev, NULL);
> +     rtnl_unlock();
> +     if (ret) {
> +             unregister_netdevice(slave_dev);

The error handling here looks sketchy.

First of all please move this unregister to the error path below, not
inside the body of the if.

Secondly as a rule of thumb the error path should resemble the destroy
function.

Here we have :

        unregister_netdevice(slave_dev);
out_phy:
        rtnl_lock();
        phylink_disconnect_phy(p->dp->pl);
        rtnl_unlock();
        phylink_destroy(p->dp->pl);
out_gcells:
        gro_cells_destroy(&p->gcells);
out_free:
        free_percpu(p->stats64);
        free_netdev(slave_dev);
        port->slave = NULL;
        return ret;

vs.

        netif_carrier_off(slave_dev);
        rtnl_lock();
        phylink_disconnect_phy(dp->pl);
        rtnl_unlock();

        dsa_slave_notify(slave_dev, DSA_PORT_UNREGISTER);
        unregister_netdev(slave_dev);
        phylink_destroy(dp->pl);
        gro_cells_destroy(&p->gcells);
        free_percpu(p->stats64);
        free_netdev(slave_dev);


Ordering is different, plus you're missing the dsa_slave_notify() and
netif_carrier_off().

> +             goto out_phy;
> +     }
>  
>       return 0;
>  
> @@ -2013,11 +2020,13 @@ int dsa_slave_create(struct dsa_port *port)
>  
>  void dsa_slave_destroy(struct net_device *slave_dev)
>  {
> +     struct net_device *master = dsa_slave_to_master(slave_dev);
>       struct dsa_port *dp = dsa_slave_to_port(slave_dev);
>       struct dsa_slave_priv *p = netdev_priv(slave_dev);
>  
>       netif_carrier_off(slave_dev);
>       rtnl_lock();
> +     netdev_upper_dev_unlink(master, slave_dev);
>       phylink_disconnect_phy(dp->pl);
>       rtnl_unlock();