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Date:   Fri, 19 Jun 2020 01:32:56 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        netdev <netdev@...r.kernel.org>,
        syzbot+f3a0e80c34b3fc28ac5e@...kaller.appspotmail.com,
        Taehee Yoo <ap420073@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [Patch net] net: change addr_list_lock back to static key

On Fri, 19 Jun 2020 at 01:30, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Thu, Jun 18, 2020 at 11:33:44PM +0300, Vladimir Oltean wrote:
> > On Thu, 18 Jun 2020 at 23:06, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > >
> > > On Thu, Jun 18, 2020 at 12:56 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> > > >
> > > > On Thu, Jun 18, 2020 at 12:40 PM Vladimir Oltean <olteanv@...il.com> wrote:
> > > > >
> > > > > It's me with the stacked DSA devices again:
> > > >
> > > > It looks like DSA never uses netdev API to link master
> > > > device with slave devices? If so, their dev->lower_level
> > > > are always 1, therefore triggers this warning.
> > > >
> > > > I think it should call one of these netdev_upper_dev_link()
> > > > API's when creating a slave device.
> > > >
> > >
> > > I don't know whether DSA is too special to use the API, but
> > > something like this should work:
> > >
> > > diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> > > index 4c7f086a047b..f7a2a281e7f0 100644
> > > --- a/net/dsa/slave.c
> > > +++ b/net/dsa/slave.c
> > > @@ -1807,6 +1807,11 @@ int dsa_slave_create(struct dsa_port *port)
> > >                            ret, slave_dev->name);
> > >                 goto out_phy;
> > >         }
> > > +       ret = netdev_upper_dev_link(slave_dev, master, NULL);
> > > +       if (ret) {
> > > +               unregister_netdevice(slave_dev);
> > > +               goto out_phy;
> > > +       }
> > >
> > >         return 0;
> > >
> > > @@ -1832,6 +1837,7 @@ void dsa_slave_destroy(struct net_device *slave_dev)
> > >         netif_carrier_off(slave_dev);
> > >         rtnl_lock();
> > >         phylink_disconnect_phy(dp->pl);
> > > +       netdev_upper_dev_unlink(slave_dev, dp->master);
> > >         rtnl_unlock();
> > >
> > >         dsa_slave_notify(slave_dev, DSA_PORT_UNREGISTER);
> >
> > Thanks. This is a good approximation of what needed to be done:
> > - netdev_upper_dev_link needs to be under rtnl,
> > - "dp->master" should be "dsa_slave_to_master(slave_dev)" since it's
> > actually a union if you look at struct dsa_port).
>
> > - And, most importantly, I think the hierarchy should be reversed: a
> > (virtual) DSA switch port net device (slave) should be an upper of the
> > (real) DSA master (the host port). Think of it like this: a DSA switch
> > is a sort of port multiplier for a host port, based on a frame header.
> > But, it works!
>
> Hi Vladimir
>
> So you are suggesting this?
>
> > > +       ret = netdev_upper_dev_link(master, slave_dev, NULL);
>
>   Andrew

Yes, basically this:

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 4c7f086a047b..6aff8cfc9cf1 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -1807,6 +1807,13 @@ 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);
+               goto out_phy;
+       }

        return 0;

@@ -1826,12 +1833,14 @@ 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();
        phylink_disconnect_phy(dp->pl);
+       netdev_upper_dev_unlink(master, slave_dev);
        rtnl_unlock();

        dsa_slave_notify(slave_dev, DSA_PORT_UNREGISTER);

Do you see a problem with it?

Thanks,
-Vladimir

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