Commit 68698970 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
Browse files

tcp: simplify tcp_mark_skb_lost 



This patch consolidates and simplifes the loss marking logic used
by a few loss detections (RACK, RFC6675, NewReno). Previously
each detection uses a subset of several intertwined subroutines.
This unncessary complexity has led to bugs (and fixes of bug fixes).

tcp_mark_skb_lost now is the single one routine to mark a packet loss
when a loss detection caller deems an skb ist lost:

   1. rewind tp->retransmit_hint_skb if skb has lower sequence or
      all lost ones have been retransmitted.

   2. book-keeping: adjust flags and counts depending on if skb was
      retransmitted or not.

Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fd214674

net/ipv4/tcp_input.c

+22 −37
Original line number Diff line number Diff line
@@ -1006,7 +1006,11 @@ static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq, 
		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);

}



/* This must be called before lost_out is incremented */

 /* This must be called before lost_out or retrans_out are updated

  * on a new loss, because we want to know if all skbs previously

  * known to be lost have already been retransmitted, indicating

  * that this newly lost skb is our next skb to retransmit.

  */

static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)

{

	if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) ||
@@ -1018,32 +1022,25 @@ static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb) 


void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)

{

	__u8 sacked = TCP_SKB_CB(skb)->sacked;

	struct tcp_sock *tp = tcp_sk(sk);



	tcp_skb_mark_lost_uncond_verify(tp, skb);

	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {

	if (sacked & TCPCB_SACKED_ACKED)

		return;



	tcp_verify_retransmit_hint(tp, skb);

	if (sacked & TCPCB_LOST) {

		if (sacked & TCPCB_SACKED_RETRANS) {

			/* Account for retransmits that are lost again */

			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;

			tp->retrans_out -= tcp_skb_pcount(skb);

			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,

				      tcp_skb_pcount(skb));

		}

	} else {

		tp->lost_out += tcp_skb_pcount(skb);

		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;

	}



/* Sum the number of packets on the wire we have marked as lost.

 * There are two cases we care about here:

 * a) Packet hasn't been marked lost (nor retransmitted),

 *    and this is the first loss.

 * b) Packet has been marked both lost and retransmitted,

 *    and this means we think it was lost again.

 */

static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)

{

	__u8 sacked = TCP_SKB_CB(skb)->sacked;



	if (!(sacked & TCPCB_LOST) ||

	    ((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))

		tp->lost += tcp_skb_pcount(skb);

}



static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
@@ -1057,17 +1054,6 @@ static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb) 
	}

}



void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)

{

	tcp_verify_retransmit_hint(tp, skb);



	tcp_sum_lost(tp, skb);

	if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {

		tp->lost_out += tcp_skb_pcount(skb);

		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;

	}

}



/* Updates the delivered and delivered_ce counts */

static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,

				bool ece_ack)
@@ -2688,8 +2674,7 @@ void tcp_simple_retransmit(struct sock *sk) 
	unsigned int mss = tcp_current_mss(sk);



	skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {

		if (tcp_skb_seglen(skb) > mss &&

		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))

		if (tcp_skb_seglen(skb) > mss)

			tcp_mark_skb_lost(sk, skb);

	}