Commit 93b174ad authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
Browse files

tcp: bug fix Fast Open client retransmission 



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: default avatarYuchung Cheng <ycheng@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1afa4717

include/net/tcp.h

+1 −0
Original line number Diff line number Diff line
@@ -525,6 +525,7 @@ static inline __u32 cookie_v6_init_sequence(struct sock *sk, 
extern void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,

				      int nonagle);

extern bool tcp_may_send_now(struct sock *sk);

extern int __tcp_retransmit_skb(struct sock *, struct sk_buff *);

extern int tcp_retransmit_skb(struct sock *, struct sk_buff *);

extern void tcp_retransmit_timer(struct sock *sk);

extern void tcp_xmit_retransmit_queue(struct sock *);

net/ipv4/tcp_input.c

+5 −1
Original line number Diff line number Diff line
@@ -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;

	}

net/ipv4/tcp_output.c

+10 −5
Original line number Diff line number Diff line
@@ -2309,12 +2309,11 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, 
 * state updates are done by the caller.  Returns non-zero if an

 * error occurred which prevented the send.

 */

int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)

int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct inet_connection_sock *icsk = inet_csk(sk);

	unsigned int cur_mss;

	int err;



	/* Inconslusive MTU probe */

	if (icsk->icsk_mtup.probe_size) {
@@ -2387,12 +2386,18 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) 
	if (unlikely(NET_IP_ALIGN && ((unsigned long)skb->data & 3))) {

		struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,

						   GFP_ATOMIC);

		err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :

		return nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :

			      -ENOBUFS;

	} else {

		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);

		return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);

	}

}



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);

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