Re: [PATCH net-next 6/6] bonding: use RCU protection for alb xmit path

[Ding Tianhong <dingtianhong@huawei.com>]

On 2013/9/3 18:22, Nikolay Aleksandrov wrote:
> On 08/30/2013 12:05 PM, Ding Tianhong wrote:
>> The commit 278b20837511776dc9d5f6ee1c7fabd5479838bb
>> (bonding: initial RCU conversion) has convert the roundrobin, active-backup,
>> broadcast and xor xmit path to rcu protection, the performance will be better
>> for these mode, so this time, convert xmit path for alb mode.
>>
>> Suggested-by: Nikolay Aleksandrov <nikolay@redhat.com>
>> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
>> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
>> Cc: Nikolay Aleksandrov <nikolay@redhat.com>
>> Cc: Veaceslav Falico <vfalico@redhat.com>
>> ---
>>  drivers/net/bonding/bond_alb.c | 20 +++++++++-----------
>>  drivers/net/bonding/bonding.h  |  2 +-
>>  2 files changed, 10 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>> index d266c56..e94a5d0 100644
>> --- a/drivers/net/bonding/bond_alb.c
>> +++ b/drivers/net/bonding/bond_alb.c
>> @@ -229,7 +229,7 @@ static struct slave *tlb_get_least_loaded_slave(struct bonding *bond)
>>  	max_gap = LLONG_MIN;
>>  
>>  	/* Find the slave with the largest gap */
>> -	bond_for_each_slave(bond, slave) {
>> +	bond_for_each_slave_rcu(bond, slave) {
>>  		if (SLAVE_IS_OK(slave)) {
>>  			long long gap = compute_gap(slave);
>>  
>> @@ -625,10 +625,12 @@ static struct slave *rlb_choose_channel(struct sk_buff *skb, struct bonding *bon
>>  {
>>  	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>>  	struct arp_pkt *arp = arp_pkt(skb);
>> -	struct slave *assigned_slave;
>> +	struct slave *assigned_slave, *curr_active_slave;
>>  	struct rlb_client_info *client_info;
>>  	u32 hash_index = 0;
>>  
>> +	curr_active_slave = rcu_dereference(bond->curr_active_slave);
>> +
> I think this code is prone to a race condition with the slave removal, because
> without the lock __bond_release_one() may think that it has done the LB release
> (bond_alb_deinit_slave) and cleared the slave while you may set it after locking.
> I guess you should move the dereference after the lock so to make sure that the
> LB release hasn't passed (or it has and it'll be different).
> 

yes, I ignore it, fix it in next version.

>>  	_lock_rx_hashtbl(bond);
>>  
>>  	hash_index = _simple_hash((u8 *)&arp->ip_dst, sizeof(arp->ip_dst));
>> @@ -654,9 +656,9 @@ static struct slave *rlb_choose_channel(struct sk_buff *skb, struct bonding *bon
>>  			 * move the old client to primary (curr_active_slave) so
>>  			 * that the new client can be assigned to this entry.
>>  			 */
>> -			if (bond->curr_active_slave &&
>> -			    client_info->slave != bond->curr_active_slave) {
>> -				client_info->slave = bond->curr_active_slave;
>> +			if (curr_active_slave &&
>> +			    client_info->slave != curr_active_slave) {
>> +				client_info->slave = curr_active_slave;
>>  				rlb_update_client(client_info);
>>  			}
>>  		}
>> @@ -1336,8 +1338,6 @@ int bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>>  
>>  	/* make sure that the curr_active_slave do not change during tx
>>  	 */
>> -	read_lock(&bond->lock);
>> -	read_lock(&bond->curr_slave_lock);
>>  
>>  	switch (ntohs(skb->protocol)) {
>>  	case ETH_P_IP: {
>> @@ -1420,12 +1420,12 @@ int bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>>  
>>  	if (!tx_slave) {
>>  		/* unbalanced or unassigned, send through primary */
>> -		tx_slave = bond->curr_active_slave;
>> +		tx_slave = rcu_dereference(bond->curr_active_slave);
>>  		bond_info->unbalanced_load += skb->len;
>>  	}
>>  
>>  	if (tx_slave && SLAVE_IS_OK(tx_slave)) {
>> -		if (tx_slave != bond->curr_active_slave) {
>> +		if (tx_slave != rcu_dereference(bond->curr_active_slave)) {
>>  			memcpy(eth_data->h_source,
>>  			       tx_slave->dev->dev_addr,
>>  			       ETH_ALEN);
>> @@ -1440,8 +1440,6 @@ int bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>>  		}
>>  	}
>>  
>> -	read_unlock(&bond->curr_slave_lock);
>> -	read_unlock(&bond->lock);
>>  	if (res) {
>>  		/* no suitable interface, frame not sent */
>>  		kfree_skb(skb);
>> diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
>> index a3ab47f..9bc3af0 100644
>> --- a/drivers/net/bonding/bonding.h
>> +++ b/drivers/net/bonding/bonding.h
>> @@ -536,7 +536,7 @@ static inline struct slave *bond_slave_has_mac(struct bonding *bond,
>>  {
>>  	struct slave *tmp;
>>  
>> -	bond_for_each_slave(bond, tmp)
>> +	bond_for_each_slave_rcu(bond, tmp)
>>  		if (ether_addr_equal_64bits(mac, tmp->dev->dev_addr))
>>  			return tmp;
>>  
>>
> 
> 
> .
>