tcp: TCP Fast Open Server - take SYNACK RTT after completing 3WHS
authorNeal Cardwell <ncardwell@google.com>
Sat, 22 Sep 2012 04:18:55 +0000 (04:18 +0000)
committerDavid S. Miller <davem@davemloft.net>
Sat, 22 Sep 2012 19:47:10 +0000 (15:47 -0400)
commit016818d076871c4ee34db1e8d74dc17ac1de626a
tree60d0f20afb0937f61b5fc4611e53a2ac411a0646
parent623df484a777f3c00c1ea3d6a7565b8d8ac688a1
tcp: TCP Fast Open Server - take SYNACK RTT after completing 3WHS

When taking SYNACK RTT samples for servers using TCP Fast Open, fix
the code to ensure that we only call tcp_valid_rtt_meas() after we
receive the ACK that completes the 3-way handshake.

Previously we were always taking an RTT sample in
tcp_v4_syn_recv_sock(). However, for TCP Fast Open connections
tcp_v4_conn_req_fastopen() calls tcp_v4_syn_recv_sock() at the time we
receive the SYN. So for TFO we must wait until tcp_rcv_state_process()
to take the RTT sample.

To fix this, we wait until after TFO calls tcp_v4_syn_recv_sock()
before we set the snt_synack timestamp, since tcp_synack_rtt_meas()
already ensures that we only take a SYNACK RTT sample if snt_synack is
non-zero. To be careful, we only take a snt_synack timestamp when
a SYNACK transmit or retransmit succeeds.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
include/net/tcp.h
net/ipv4/tcp_input.c
net/ipv4/tcp_ipv4.c
net/ipv6/tcp_ipv6.c