netdev - Re: [PATCH net v2 1/3] net: bonding: Unsync device addresses on ndo

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Date:   Mon, 5 Sep 2022 18:19:35 +0900
From:   Benjamin Poirier <bpoirier@...dia.com>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     netdev@...r.kernel.org, Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Jiri Pirko <jiri@...nulli.us>,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Toppins <jtoppins@...hat.com>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net v2 1/3] net: bonding: Unsync device addresses on
 ndo_stop

On 2022-09-02 11:28 -0700, Jay Vosburgh wrote:
> Benjamin Poirier <bpoirier@...dia.com> wrote:
> 
> 	Repeating a couple of questions that I suspect were missed the
> first time around:

Thanks for repeating, I did miss the other questions, sorry.

[...]
> >@@ -2171,12 +2169,8 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
> > 		dev_uc_sync_multiple(slave_dev, bond_dev);
> > 		netif_addr_unlock_bh(bond_dev);
> > 
> >-		if (BOND_MODE(bond) == BOND_MODE_8023AD) {
> >-			/* add lacpdu mc addr to mc list */
> >-			u8 lacpdu_multicast[ETH_ALEN] = MULTICAST_LACPDU_ADDR;
> >-
> >+		if (BOND_MODE(bond) == BOND_MODE_8023AD)
> > 			dev_mc_add(slave_dev, lacpdu_multicast);
> >-		}
> > 	}
> 
> 	Just to make sure I'm clear (not missing something in the
> churn), the above changes regarding lacpdu_multicast have no functional
> impact, correct?  They appear to move lacpdu_multicast to global scope
> for use in the change just below.

Yes, that's right - no functional impact. I'll split that to a separate
patch to make it clearer.

> > 	bond->slave_cnt++;
> >@@ -4211,6 +4205,9 @@ static int bond_open(struct net_device *bond_dev)
> > 		/* register to receive LACPDUs */
> > 		bond->recv_probe = bond_3ad_lacpdu_recv;
> > 		bond_3ad_initiate_agg_selection(bond, 1);
> >+
> >+		bond_for_each_slave(bond, slave, iter)
> >+			dev_mc_add(slave->dev, lacpdu_multicast);
> > 	}
> 
> 	After this change, am I understanding correctly that both
> bond_enslave() and bond_open() will call dev_mc_add() for
> lacpdu_multicast?  Since dev_mc_add() -> __dev_mc_add() calls
> __hw_addr_add_ex() with sync=false and exclusive=false, could that allow
> us to end up with two references for lacpdu_multicast?

You are correct once again. When enslaving to an up bond (case in the
selftest), it is ok, but when enslaving to a down bond and then setting
it up, there is a double add.

Thanks for the review. I'll send a v3.