Subject: Re: [PATCH] bonding: Fix corrupted queue_mapping

From: John Fastabend <[email-masked]>
Date: Fri, 08 Jun 2012 00:42:25 -0700

On 6/8/2012 12:23 AM, Eric Dumazet wrote:
> On Fri, 2012-06-08 at 08:47 +0200, Eric Dumazet wrote:
>> On Thu, 2012-06-07 at 23:15 -0700, David Miller wrote:
>>> From: Eric Dumazet <[email-masked]>
>>> Date: Fri, 08 Jun 2012 08:11:21 +0200
>>>
>>>> On Thu, 2012-06-07 at 23:02 -0700, David Miller wrote:
>>>>> Hmmm, isn't that what qdisc_skb_cb is for?  And even private data is
>>>>> explicitly allocated:
>>>>>
>>>>>>   	unsigned char		data[24];
>>>>>
>>>>> there. :-)
>>>>>
>>>>
>>>> Yes, but some other layers can use the same trick so it might collide.
>>>>
>>>> Inserting the bond field in qdisc_skb_cb (level0) is safer.
>>>
>>> Do you suggest that Infiniband does the same thing? :-)
>>
>> I wonder if another way to solve this is not letting ndo_select_queue()
>> method the responsibility to call skb_set_queue_mapping() itself ?
>>
>> (ie removing skb_set_queue_mapping() done in dev_pick_tx())
>>
>> bonding would not have to save/restore skb queue mapping ?
>>
>> Partial patch : (we have to audit all ndo_select_queue()
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index cd09819..c6c92d5 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2368,6 +2368,7 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev,
>>
>>   	if (dev->real_num_tx_queues == 1)
>>   		queue_index = 0;
>> +		skb_set_queue_mapping(skb, queue_index);
>>   	else if (ops->ndo_select_queue) {
>>   		queue_index = ops->ndo_select_queue(dev, skb);
>>   		queue_index = dev_cap_txqueue(dev, queue_index);
>> @@ -2391,9 +2392,9 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev,
>>   					sk_tx_queue_set(sk, queue_index);
>>   			}
>>   		}
>> +		skb_set_queue_mapping(skb, queue_index);
>>   	}
>>
>> -	skb_set_queue_mapping(skb, queue_index);
>>   	return netdev_get_tx_queue(dev, queue_index);
>>   }
>>
>>
>
>
> I must say I dont understand dev_pick_tx() anymore.
>
> It seems to ignore skb->queue_mapping (unless device provides its own
> ndo_select_queue() and this functions is aware of skb->queue_mapping, as
> correctly done in ixgbe)
>
> So commit fff3269907897ee (tcp: reflect SYN queue_mapping into SYNACK
> packets) works on ixgbe, but probably not on other multiqueue devices.
>
> This sounds like a regression to me.
>
>
>

Well it would get picked up via skb_tx_hash(),

         else if (ops->ndo_select_queue) {
		[...]
         } else {
                 struct sock *sk = skb->sk;
                 queue_index = sk_tx_queue_get(sk);

                 if (queue_index < 0 || skb->ooo_okay ||
                     queue_index >= dev->real_num_tx_queues) {
                         int old_index = queue_index;

                         queue_index = get_xps_queue(dev, skb);
                         if (queue_index < 0)
                                 queue_index = skb_tx_hash(dev, skb);
	[...]

So think this might be OK.