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tcp: simplify tcp_mark_skb_lost

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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: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng 2020-09-25 10:04:30 -07:00 committed by David S. Miller
parent fd2146741c
commit 686989700c
1 changed files with 22 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
net/ipv4/tcp_input.c
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@ -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) ||
@ -1018,34 +1022,27 @@ 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) {
/* 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));
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)
{
if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
@ -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);
}