Subject: Re: [PATCH net-next] bonding: move bond-specific init after enslave happens

From: Veaceslav Falico <[email-masked]>
Date: Mon, 21 Oct 2013 09:03:53 +0200

On Mon, Oct 21, 2013 at 09:35:09AM +0800, Ding Tianhong wrote:
>On 2013/10/20 20:47, Veaceslav Falico wrote:
>> As Jiri noted, currently we first do all bonding-specific initialization
>> (specifically - bond_select_active_slave(bond)) before we actually attach
>> the slave (so that it becomes visible through bond_for_each_slave() and
>> friends). This might result in bond_select_active_slave() not seeing the
>> first/new slave and, thus, not actually selecting an active slave.
>>
>> Fix this by moving all the bond-related init part after we've actually
>> completely initialized and linked (via bond_master_upper_dev_link()) the
>> new slave.
>>
>> After this we have all the initialization of the new slave *before*
>> linking, and all the stuff that needs to be done on bonding *after* it. It
>> has also a bonus effect - we can remove the locking on the new slave init
>> completely, and only use it for bond_select_active_slave().
>>
>> Reported-by: Jiri Pirko <[email-masked]>
>> CC: Jay Vosburgh <[email-masked]>
>> CC: Andy Gospodarek <[email-masked]>
>> Signed-off-by: Veaceslav Falico <[email-masked]>
>> ---
>>  drivers/net/bonding/bond_main.c | 29 ++++++++++-------------------
>>  1 file changed, 10 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>> index d90734f..047c0fb 100644
>> --- a/drivers/net/bonding/bond_main.c
>> +++ b/drivers/net/bonding/bond_main.c
>> @@ -1471,22 +1471,14 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>  		goto err_close;
>>  	}
>>
>> -	write_lock_bh(&bond->lock);
>> -
>>  	prev_slave = bond_last_slave(bond);
>>  	bond_attach_slave(bond, new_slave);
>>
>>  	new_slave->delay = 0;
>>  	new_slave->link_failure_count = 0;
>>
>> -	write_unlock_bh(&bond->lock);
>> -
>> -	bond_compute_features(bond);
>> -
>>  	bond_update_speed_duplex(new_slave);
>>
>> -	read_lock(&bond->lock);
>> -
>>  	new_slave->last_arp_rx = jiffies -
>>  		(msecs_to_jiffies(bond->params.arp_interval) + 1);
>>  	for (i = 0; i < BOND_MAX_ARP_TARGETS; i++)
>> @@ -1547,12 +1539,9 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>  		}
>>  	}
>>
>> -	write_lock_bh(&bond->curr_slave_lock);
>> -
>>  	switch (bond->params.mode) {
>>  	case BOND_MODE_ACTIVEBACKUP:
>>  		bond_set_slave_inactive_flags(new_slave);
>> -		bond_select_active_slave(bond);
>>  		break;
>>  	case BOND_MODE_8023AD:
>>  		/* in 802.3ad mode, the internal mechanism
>> @@ -1578,7 +1567,6 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>  	case BOND_MODE_ALB:
>>  		bond_set_active_slave(new_slave);
>>  		bond_set_slave_inactive_flags(new_slave);
>> -		bond_select_active_slave(bond);
>>  		break;
>>  	default:
>>  		pr_debug("This slave is always active in trunk mode\n");
>> @@ -1596,10 +1584,6 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>  		break;
>>  	} /* switch(bond_mode) */
>>
>> -	write_unlock_bh(&bond->curr_slave_lock);
>> -
>> -	bond_set_carrier(bond);
>> -
>>  #ifdef CONFIG_NET_POLL_CONTROLLER
>>  	slave_dev->npinfo = bond->dev->npinfo;
>>  	if (slave_dev->npinfo) {
>> @@ -1614,8 +1598,6 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>  	}
>>  #endif
>>
>> -	read_unlock(&bond->lock);
>> -
>>  	res = netdev_rx_handler_register(slave_dev, bond_handle_frame,
>>  					 new_slave);
>>  	if (res) {
>> @@ -1629,6 +1611,16 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>  		goto err_unregister;
>>  	}
>>
>> +	bond_compute_features(bond);
>> +	bond_set_carrier(bond);
>> +
>> +	if (USES_PRIMARY(bond->params.mode)) {
>> +		read_lock(&bond->lock);
>> +		write_lock_bh(&bond->curr_slave_lock);
>> +		bond_select_active_slave(bond);
>> +		write_unlock_bh(&bond->curr_slave_lock);
>> +		read_unlock(&bond->lock);
>> +	}
>>
>
>agree to move the lock, and I think bond_attach_slave() should add here,
>as it look more logical, the slave_cnt should not add before the slave truly
>add to the bond.

bond_(de)attach_slave() should be removed completely, actually. we don't
need special functions for ++/--.

OTOH, the whole slave_cnt is flawed a bit, whilst using RCU - we can never
guarantee that it's the actual value if we don't hold rtnl lock (we do in
ioctl, but we don't in the hash functions).

I'll take a closer look and send v2.

>
>Regards.
>Ding
>
>>  	pr_info("%s: enslaving %s as a%s interface with a%s link.\n",
>>  		bond_dev->name, slave_dev->name,
>> @@ -1686,7 +1678,6 @@ err_free:
>>  	kfree(new_slave);
>>
>>  err_undo_flags:
>> -	bond_compute_features(bond);
>>  	/* Enslave of first slave has failed and we need to fix master's mac */
>>  	if (!bond_has_slaves(bond) &&
>>  	    ether_addr_equal(bond_dev->dev_addr, slave_dev->dev_addr))
>>
>
>