Subject: Re: [PATCH net-next V3 3/3] net: Add GRO support for vxlan traffic

From: Or Gerlitz <[email-masked]>
Date: Thu, 9 Jan 2014 08:32:24 +0200

On 09/01/2014 00:11, Eric Dumazet wrote:
> On Wed, 2014-01-08 at 22:34 +0200, Or Gerlitz wrote:
>
>> +
>>   /* Notify netdevs that UDP port started listening */
>> -static void vxlan_notify_add_rx_port(struct sock *sk)
>> +static void vxlan_notify_add_rx_port(struct vxlan_sock *vs)
>>   {
>>   	struct net_device *dev;
>> +	struct sock *sk = vs->sock->sk;
>>   	struct net *net = sock_net(sk);
>>   	sa_family_t sa_family = sk->sk_family;
>>   	__be16 port = inet_sk(sk)->inet_sport;
>> @@ -569,12 +671,16 @@ static void vxlan_notify_add_rx_port(struct sock *sk)
>>   							    port);
>>   	}
>>   	rcu_read_unlock();
>> +
>> +	if (sa_family == AF_INET)
>> +		call_rcu(&vs->rcu, vxlan_add_udp_offload);
> Why waiting RCU grace period here?

Basically the add operation can be done right away, however, since the 
delete operation can't be done
instantly when we want it, I wanted to protect against a series of 
add/del/add in times T1 < T2 < T3

T1 add(X)
T2 del(X)
T3 add(X)

where the delete is deferred and as a result the 2nd add is done before 
the delete and @ the end offload X is not added in the 2nd time.From 
your other comment below I conclude that I probably miss something about 
the rcu usage here, so will give it further thought.

>
>>   }
>>   
>>   /* Notify netdevs that UDP port is no more listening */
>> -static void vxlan_notify_del_rx_port(struct sock *sk)
>> +static void vxlan_notify_del_rx_port(struct vxlan_sock *vs)
>>   {
>>   	struct net_device *dev;
>> +	struct sock *sk = vs->sock->sk;
>>   	struct net *net = sock_net(sk);
>>   	sa_family_t sa_family = sk->sk_family;
>>   	__be16 port = inet_sk(sk)->inet_sport;
>> @@ -586,6 +692,9 @@ static void vxlan_notify_del_rx_port(struct sock *sk)
>>   							    port);
>>   	}
>>   	rcu_read_unlock();
>> +
>> +	if (sa_family == AF_INET)
>> +		call_rcu(&vs->rcu, vxlan_del_udp_offload);
>>   }
> This looks buggy.
>
> You need to :
>
> 1) remove the offload structure from list
> 2) Then wait rcu grace period, and finally free the memory
>
>
>