| From 96810d919233616a8c5b3a3a9f0c8ba87f5d3499 Mon Sep 17 00:00:00 2001 |
| From: Pengcheng Yang <yangpc@wangsu.com> |
| Date: Tue, 14 Jan 2020 17:23:40 +0800 |
| Subject: [PATCH] tcp: fix marked lost packets not being retransmitted |
| |
| commit e176b1ba476cf36f723cfcc7a9e57f3cb47dec70 upstream. |
| |
| When the packet pointed to by retransmit_skb_hint is unlinked by ACK, |
| retransmit_skb_hint will be set to NULL in tcp_clean_rtx_queue(). |
| If packet loss is detected at this time, retransmit_skb_hint will be set |
| to point to the current packet loss in tcp_verify_retransmit_hint(), |
| then the packets that were previously marked lost but not retransmitted |
| due to the restriction of cwnd will be skipped and cannot be |
| retransmitted. |
| |
| To fix this, when retransmit_skb_hint is NULL, retransmit_skb_hint can |
| be reset only after all marked lost packets are retransmitted |
| (retrans_out >= lost_out), otherwise we need to traverse from |
| tcp_rtx_queue_head in tcp_xmit_retransmit_queue(). |
| |
| Packetdrill to demonstrate: |
| |
| // Disable RACK and set max_reordering to keep things simple |
| 0 `sysctl -q net.ipv4.tcp_recovery=0` |
| +0 `sysctl -q net.ipv4.tcp_max_reordering=3` |
| |
| // Establish a connection |
| +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 |
| +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 |
| +0 bind(3, ..., ...) = 0 |
| +0 listen(3, 1) = 0 |
| |
| +.1 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7> |
| +0 > S. 0:0(0) ack 1 <...> |
| +.01 < . 1:1(0) ack 1 win 257 |
| +0 accept(3, ..., ...) = 4 |
| |
| // Send 8 data segments |
| +0 write(4, ..., 8000) = 8000 |
| +0 > P. 1:8001(8000) ack 1 |
| |
| // Enter recovery and 1:3001 is marked lost |
| +.01 < . 1:1(0) ack 1 win 257 <sack 3001:4001,nop,nop> |
| +0 < . 1:1(0) ack 1 win 257 <sack 5001:6001 3001:4001,nop,nop> |
| +0 < . 1:1(0) ack 1 win 257 <sack 5001:7001 3001:4001,nop,nop> |
| |
| // Retransmit 1:1001, now retransmit_skb_hint points to 1001:2001 |
| +0 > . 1:1001(1000) ack 1 |
| |
| // 1001:2001 was ACKed causing retransmit_skb_hint to be set to NULL |
| +.01 < . 1:1(0) ack 2001 win 257 <sack 5001:8001 3001:4001,nop,nop> |
| // Now retransmit_skb_hint points to 4001:5001 which is now marked lost |
| |
| // BUG: 2001:3001 was not retransmitted |
| +0 > . 2001:3001(1000) ack 1 |
| |
| Signed-off-by: Pengcheng Yang <yangpc@wangsu.com> |
| Acked-by: Neal Cardwell <ncardwell@google.com> |
| Tested-by: Neal Cardwell <ncardwell@google.com> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c |
| index b38eb72b8e67..c1358132702f 100644 |
| --- a/net/ipv4/tcp_input.c |
| +++ b/net/ipv4/tcp_input.c |
| @@ -909,9 +909,10 @@ static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq, |
| /* This must be called before lost_out is incremented */ |
| static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb) |
| { |
| - if (!tp->retransmit_skb_hint || |
| - before(TCP_SKB_CB(skb)->seq, |
| - TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) |
| + if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) || |
| + (tp->retransmit_skb_hint && |
| + before(TCP_SKB_CB(skb)->seq, |
| + TCP_SKB_CB(tp->retransmit_skb_hint)->seq))) |
| tp->retransmit_skb_hint = skb; |
| } |
| |
| -- |
| 2.7.4 |
| |