Re: [PATCH] af_packet: Raw socket destruction warning fix

[Vaneet Narang]

Hi,

>> __do_softirq
>> run_ksoftirqd
>>
>> Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
>> Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>

> Thanks for the fix. While it fixes the WARN_ON(), I believe some more
> investigation is needed here on why it is happening:
>
> We call first into packet_release(), which removes the socket hook from
> the kernel (unregister_prot_hook()), later calls synchronize_net() to
> make sure no more skbs will come in. The receive queue is purged right
> after the synchronize_net() already.
>
> packet_sock_destruct() will be called afterwards, when there are no more
> refs on the socket anymore and no af_packet skbs in tx waiting for completion.
> Only then, in sk_destruct(), we'll call into packet_sock_destruct().
>
> So, eventually double purging the sk_receive_queue seems not the right
> thing to do at first look, and w/o any deeper analysis in the commit description.
>
> Could you look a bit further into the issue? Do you have a reproducer to
> trigger it?


It is Suspend Resume scenario and in this case close(sock_id) is 
not called and hence packet_release is also not called. 
In case of suspend, driver power down its ethernet port and release all the
sk_buff stored in RX and TX ring. driver calls dev_kfree_skb_any to release all
the sk_buff in tx ring and if last tx buff of socket is called then 
packet_sock_destruct() will be invoked and will result in warning if and recevive sk_buff is 
still in receive queue. 

Driver calls dev_kfree_skb_any->dev_kfree_skb_irq 
and it adds buffer in completion queue to free and raises softirq NET_TX_SOFTIRQ

net_tx_action->__kfree_skb->skb_release_all->skb_release_head_state->sock_wfree->
__sk_free->packet_sock_destruct 

Also purging of receive queue has been taken care in other protocols.
// IP protocol
void inet_sock_destruct(struct sock *sk)
{
        struct inet_sock *inet = inet_sk(sk);

        __skb_queue_purge(&sk->sk_receive_queue);   // Purge Receive queue
        __skb_queue_purge(&sk->sk_error_queue);

.... 

         WARN_ON(atomic_read(&sk->sk_rmem_alloc));
        WARN_ON(atomic_read(&sk->sk_wmem_alloc));
 }

So i think it should be done in Raw sockets also.

>> ---
>>   net/packet/af_packet.c |    1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
>> index 81b4b81..bcb37ba 100644

Thanks
Vaneet Narang