From 686989700cabc444f25c1f1eb022aca8f2fc14b2 Mon Sep 17 00:00:00 2001
From: Yuchung Cheng <ycheng@google.com>
Date: Fri, 25 Sep 2020 10:04:30 -0700
Subject: [PATCH] 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: 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>
---
net/ipv4/tcp_input.c | 59 +++++++++++++++++---------------------------
1 file changed, 22 insertions(+), 37 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1cf4fcf8f41bf..63417c400b53f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -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) {
- /* 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));
- }
-}
-
-/* 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_SACKED_ACKED)
+ return;
- if (!(sacked & TCPCB_LOST) ||
- ((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
- tp->lost += tcp_skb_pcount(skb);
+ 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;
+ }
}
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);
}