netdev - Re: [PATCH net v4 1/2] net: sched: tbf: fix calculation of max

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Date:	Mon, 02 Dec 2013 20:59:53 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yang Yingliang <yangyingliang@...wei.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, brouer@...hat.com,
	jpirko@...hat.com, jbrouer@...hat.com
Subject: Re: [PATCH net v4 1/2] net: sched: tbf: fix calculation of max_size

On Tue, 2013-12-03 at 11:26 +0800, Yang Yingliang wrote:

> +	for (max_size = 0; max_size < MAX_PKT_LEN; max_size++)
> +		if (psched_l2t_ns(&q->rate, max_size) > q->buffer)
> +			break;
> +	if (--max_size <= 0)
> +		goto unlock_done;
> +

This seems dubious. With your new code, max_size < 65536

Prior code had :

for (n = 0; n < 256; n++)
    if (rtab->data[n] > qopt->buffer)
        break;
max_size = (n << qopt->rate.cell_log) - 1;

So we could have much bigger max_size.

The reason I ask is that its possible to have qdisc_pkt_len(skb) being
bigger than 65536, for TCP packets with low MSS value.



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