Re: [PATCH] bonding: Fix corrupted queue_mapping

On 6/8/2012 12:23 AM, Eric Dumazet wrote:

On Fri, 2012-06-08 at 08:47 +0200, Eric Dumazet wrote:

quoted

On Thu, 2012-06-07 at 23:15 -0700, David Miller wrote:

quoted

From: Eric Dumazet <redacted>
Date: Fri, 08 Jun 2012 08:11:21 +0200

quoted

On Thu, 2012-06-07 at 23:02 -0700, David Miller wrote:

quoted

Hmmm, isn't that what qdisc_skb_cb is for?  And even private data is
explicitly allocated:

quoted

  	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.