aboutsummaryrefslogtreecommitdiffstats
path: root/net
diff options
context:
space:
mode:
authorPengcheng Yang <yangpc@wangsu.com>2020-01-14 17:23:40 +0800
committerDavid S. Miller <davem@davemloft.net>2020-01-15 22:34:31 +0100
commite176b1ba476cf36f723cfcc7a9e57f3cb47dec70 (patch)
treedd2eb627a1e14ce26a314f3bd194a529f978ce4b /net
parent8b792f84c6377b27235fef16f5e78a59f890b3e1 (diff)
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')
-rw-r--r--net/ipv4/tcp_input.c7
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;
}

Privacy Policy