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

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Message-ID: <20200713173319.zjmqjzqmjcxw6gyf@skbuf>
Date:   Mon, 13 Jul 2020 20:33:19 +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

On Mon, Jul 13, 2020 at 08:30:49PM +0300, Vladimir Oltean wrote:
> 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

I mean it doesn't work when netdev_upper_dev_link() is _before_
register_netdev().

> 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