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tcp: bug fix Fast Open client retransmission

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If SYN-ACK partially acks SYN-data, the client retransmits the
remaining data by tcp_retransmit_skb(). This increments lost recovery
state variables like tp->retrans_out in Open state. If loss recovery
happens before the retransmission is acked, it triggers the WARN_ON
check in tcp_fastretrans_alert(). For example: the client sends
SYN-data, gets SYN-ACK acking only ISN, retransmits data, sends
another 4 data packets and get 3 dupacks.

Since the retransmission is not caused by network drop it should not
update the recovery state variables. Further the server may return a
smaller MSS than the cached MSS used for SYN-data, so the retranmission
needs a loop. Otherwise some data will not be retransmitted until timeout
or other loss recovery events.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng
2012-12-06 08:45:32 +00:00
committed by David S. Miller
parent 1afa471706
commit 93b174ad71
3 changed files with 16 additions and 6 deletions
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6
net/ipv4/tcp_input.c
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@@ -5645,7 +5645,11 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
tcp_fastopen_cache_set(sk, mss, cookie, syn_drop);
if (data) { /* Retransmit unacked data in SYN */
tcp_retransmit_skb(sk, data);
tcp_for_write_queue_from(data, sk) {
if (data == tcp_send_head(sk) ||
__tcp_retransmit_skb(sk, data))
break;
}
tcp_rearm_rto(sk);
return true;
}