tcp: update skb->skb_mstamp more carefully
liujian reported a problem in TCP_USER_TIMEOUT processing with a patch
in tcp_probe_timer() :
https://www.spinics.net/lists/netdev/msg454496.html
After investigations, the root cause of the problem is that we update
skb->skb_mstamp of skbs in write queue, even if the attempt to send a
clone or copy of it failed. One reason being a routing problem.
This patch prevents this, solving liujian issue.
It also removes a potential RTT miscalculation, since
__tcp_retransmit_skb() is not OR-ing TCP_SKB_CB(skb)->sacked with
TCPCB_EVER_RETRANS if a failure happens, but skb->skb_mstamp has
been changed.
A future ACK would then lead to a very small RTT sample and min_rtt
would then be lowered to this too small value.
Tested:
# cat user_timeout.pkt
--local_ip=192.168.102.64
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
+0 `ifconfig tun0 192.168.102.64/16; ip ro add 192.0.2.1 dev tun0`
+0 < S 0:0(0) win 0 <mss 1460>
+0 > S. 0:0(0) ack 1 <mss 1460>
+.1 < . 1:1(0) ack 1 win 65530
+0 accept(3, ..., ...) = 4
+0 setsockopt(4, SOL_TCP, TCP_USER_TIMEOUT, [3000], 4) = 0
+0 write(4, ..., 24) = 24
+0 > P. 1:25(24) ack 1 win 29200
+.1 < . 1:1(0) ack 25 win 65530
//change the ipaddress
+1 `ifconfig tun0 192.168.0.10/16`
+1 write(4, ..., 24) = 24
+1 write(4, ..., 24) = 24
+1 write(4, ..., 24) = 24
+1 write(4, ..., 24) = 24
+0 `ifconfig tun0 192.168.102.64/16`
+0 < . 1:2(1) ack 25 win 65530
+0 `ifconfig tun0 192.168.0.10/16`
+3 write(4, ..., 24) = -1
# ./packetdrill user_timeout.pkt
Signed-off-by: Eric Dumazet <edumazet@googl.com>
Reported-by: liujian <liujian56@huawei.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed
