diff options
| author | Pengcheng Yang <yangpc@wangsu.com> | 2020-01-14 12:23:40 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2020-01-16 00:34:31 +0300 |
| commit | e176b1ba476cf36f723cfcc7a9e57f3cb47dec70 (patch) | |
| tree | dd2eb627a1e14ce26a314f3bd194a529f978ce4b /net/ipv4/tcp_input.c | |
| parent | 8b792f84c6377b27235fef16f5e78a59f890b3e1 (diff) | |
| download | linux-e176b1ba476cf36f723cfcc7a9e57f3cb47dec70.tar.xz | |
tcp: fix marked lost packets not being retransmitted
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>
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 0238b554a1f0..5347ab2c9c58 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; } |