From c84a57113f59486e6688be1cd443b96e3118efa0 Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Fri, 28 Feb 2014 16:42:26 -0800 Subject: tcp: fix bogus RTT on special retransmission RTT may be bogus with tall loss probe (TLP) when a packet is retransmitted and latter (s)acked without TCPCB_SACKED_RETRANS flag. For example, TLP calls __tcp_retransmit_skb() instead of tcp_retransmit_skb(). The skb timestamps are updated but the sacked flag is not marked with TCPCB_SACKED_RETRANS. As a result we'll get bogus RTT in tcp_clean_rtx_queue() or in tcp_sacktag_one() on spurious retransmission. The fix is to apply the sticky flag TCP_EVER_RETRANS to enforce Karn's check on RTT sampling. However this will disable F-RTO if timeout occurs after TLP, by resetting undo_marker in tcp_enter_loss(). We relax this check to only if any pending retransmists are still in-flight. Signed-off-by: Yuchung Cheng Acked-by: Eric Dumazet Acked-by: Neal Cardwell Acked-by: Nandita Dukkipati Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) (limited to 'net/ipv4/tcp_output.c') diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index d718482fd11c..f0eb4e337ec8 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2337,6 +2337,7 @@ 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) { @@ -2400,11 +2401,15 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) skb_headroom(skb) >= 0xFFFF)) { struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC); - return nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) : - -ENOBUFS; + err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) : + -ENOBUFS; } else { - return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); + err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); } + + if (likely(!err)) + TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS; + return err; } int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) -- cgit v1.2.3