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

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Date:   Mon, 13 Jul 2020 20:30:49 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, f.fainelli@...il.com,
        vivien.didelot@...il.com, xiyou.wangcong@...il.com,
        ap420073@...il.com
Subject: Re: [PATCH net] net: dsa: link interfaces with the DSA master to get
 rid of lockdep warnings

Hi Andrew,

On Mon, Jul 13, 2020 at 06:47:28PM +0200, Andrew Lunn 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);
> > +		goto out_phy;
> > +	}
> 
> Hi Vladimir
> 
> A common pattern we see in bugs is that the driver sets up something
> critical after calling register_netdev(), not realising that that call
> can go off and really start using the interface before it returns. So
> in general, i like to have register_netdev() last, nothing after it.
> 
> Please could you move this before register_netdev().
> 
> Thanks
> 	Andrew

It doesn't work after register_netdev(). The call to
netdev_upper_dev_link() fails and no network interface gets probed. VLAN
performs registration and linkage in the same order:

https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/net/8021q/vlan.c#n175

So I think this part is fine.

Thanks,
-Vladimir