From: Pengcheng Yang <yangpc@wangsu.com>
To: edumazet@google.com
Cc: davem@davemloft.net, kuznet@ms2.inr.ac.ru,
yoshfuji@linux-ipv6.org, ast@kernel.org, daniel@iogearbox.net,
kafai@fb.com, songliubraving@fb.com, yhs@fb.com, andriin@fb.com,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Pengcheng Yang <yangpc@wangsu.com>
Subject: [PATCH] tcp: fix marked lost packets not being retransmitted
Date: Tue, 14 Jan 2020 17:23:40 +0800 [thread overview]
Message-ID: <1578993820-2114-1-git-send-email-yangpc@wangsu.com> (raw)
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>
---
net/ipv4/tcp_input.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0238b55..5347ab2 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -915,9 +915,10 @@ 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;
}
--
1.8.3.1
next reply other threads:[~2020-01-14 9:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 9:23 Pengcheng Yang [this message]
2020-01-14 15:26 ` [PATCH] tcp: fix marked lost packets not being retransmitted Neal Cardwell
2020-01-14 16:05 ` Eric Dumazet
2020-01-14 18:39 ` Yuchung Cheng
2020-01-15 6:58 ` Pengcheng Yang
2020-01-15 21:35 ` David Miller
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