From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH v2 2/3] net_sched: Add accessor function for packet
 length for qdiscs
Date: Fri, 25 Jul 2008 04:52:15 -0700 (PDT)
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From: Jarek Poplawski <jarkao2@gmail.com>
Date: Fri, 25 Jul 2008 11:53:55 +0000

> On Fri, Jul 25, 2008 at 11:37:57AM +0000, Jarek Poplawski wrote:
>
> As a matter of fact it's a good example: in your patch we have this:
> 
> +		ret = cl->un.leaf.q->enqueue(skb, cl->un.leaf.q);
> +		if (ret == NET_XMIT_DROP) {
> +			sch->qstats.drops++;
> +			cl->qstats.drops++;
> +		} else {
> +			cl->bstats.packets +=
> +				skb_is_gso(skb)?skb_shinfo(skb)->gso_segs:1;
> +			cl->bstats.bytes += skb->len;
> 
> So, if something works like noop_enqueue() and returns NET_XMIT_CN
> here, we're just using skb after kfree...

noop_enqueue() can only be a root qdisc, never a leaf hanging off of a
class

What TCP depends upon is that DROP means DROP, and that the
packet never reached the device and has been freed.