tcp_retransmit statistics Error In higher than 4.7 of kernel version

[jundizhou]

Describe the bug
tcp_retransmit statistics Error In higher than 4.7 of kernel version

Higher than 4.7 source code

int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int err = __tcp_retransmit_skb(sk, skb, segs);

	if (err == 0) {
#if FASTRETRANS_DEBUG > 0
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
			net_dbg_ratelimited("retrans_out leaked\n");
		}
#endif
		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
		tp->retrans_out += tcp_skb_pcount(skb);

		/* Save stamp of the first retransmit. */
		if (!tp->retrans_stamp)
			tp->retrans_stamp = tcp_skb_timestamp(skb);

	}

	if (tp->undo_retrans < 0)
		tp->undo_retrans = 0;
	tp->undo_retrans += tcp_skb_pcount(skb);
	return err;
}

Lower than 4.7 source code

int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int err = __tcp_retransmit_skb(sk, skb);

	if (err == 0) {
		/* Update global TCP statistics. */
		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);

		tp->total_retrans++;

#if FASTRETRANS_DEBUG > 0
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
			net_dbg_ratelimited("retrans_out leaked\n");
		}
#endif
		if (!tp->retrans_out)
			tp->lost_retrans_low = tp->snd_nxt;
		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
		tp->retrans_out += tcp_skb_pcount(skb);

		/* Save stamp of the first retransmit. */
		if (!tp->retrans_stamp)
			tp->retrans_stamp = TCP_SKB_CB(skb)->when;

		tp->undo_retrans += tcp_skb_pcount(skb);

		/* snd_nxt is stored to detect loss of retransmitted segment,
		 * see tcp_input.c tcp_sacktag_write_queue().
		 */
		TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
	}
	return err;
}

Why the bug
In higher than 4.7, SEGS parameter represents the number of packet losses, which should be counted instead of 1

[dxsup]

Closed via #450