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Date:   Thu, 18 Jun 2020 13:59:53 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     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 Thu, Jun 18, 2020 at 1:33 PM Vladimir Oltean <olteanv@...il.com> 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!

Please feel free to make any changes you need and submit it
by yourself, as you know DSA better than me and I do not even
have a DSA testing environment.

>
> Do you mind if I submit your modified patch to "net"? What would be an
> adequate Fixes: tag?

If it is merely to fix the lockdep warning, my commit 845e0ebb4408d447
is the right one to blame.

Thanks.

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