netdev - Re: [PATCH RFC net-next] pktgen: introduce 'rx' mode

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Date:	Tue, 28 Apr 2015 21:14:13 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Thomas Graf <tgraf@...g.ch>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next] pktgen: introduce 'rx' mode

On Tue, 2015-04-28 at 19:11 -0700, Alexei Starovoitov wrote:

> +	if (pkt_dev->flags & F_DO_RX) {
> +		local_bh_disable();
> +		atomic_add(burst, &pkt_dev->skb->users);
> +		do {
> +			ret = netif_receive_skb(pkt_dev->skb);
> +			if (ret == NET_RX_DROP)
> +				pkt_dev->errors++;
> +			pkt_dev->last_ok = 1;
> +			pkt_dev->sofar++;
> +			pkt_dev->seq_num++;
> +		} while (--burst > 0);
> +		local_bh_enable();
> +		goto out;
> +	}
> +

This looks buggy.

skb can be put on a queue, so skb->next and skb->prev cannot be reused,
or queues will be corrupted.

Note that on TX, it is possible to have the same issue if you use a
virtual device like bonding, and skb is queued on a slave qdisc.

(Thats why we have this IFF_TX_SKB_SHARING flag)



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