From: Alexander Duyck alexanderduyck@fb.com
[ Upstream commit 55472017a4219ca965a957584affdb17549ae4a4 ]
When setting congestion control via a BPF program it is seen that the SYN/ACK for packets within a given flow will not include the ECT0 flag. A bit of simple printk debugging shows that when this is configured without BPF we will see the value INET_ECN_xmit value initialized in tcp_assign_congestion_control however when we configure this via BPF the socket is in the closed state and as such it isn't configured, and I do not see it being initialized when we transition the socket into the listen state. The result of this is that the ECT0 bit is configured based on whatever the default state is for the socket.
Any easy way to reproduce this is to monitor the following with tcpdump: tools/testing/selftests/bpf/test_progs -t bpf_tcp_ca
Without this patch the SYN/ACK will follow whatever the default is. If dctcp all SYN/ACK packets will have the ECT0 bit set, and if it is not then ECT0 will be cleared on all SYN/ACK packets. With this patch applied the SYN/ACK bit matches the value seen on the other packets in the given stream.
Fixes: 91b5b21c7c16 ("bpf: Add support for changing congestion control") Signed-off-by: Alexander Duyck alexanderduyck@fb.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_cong.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -196,6 +196,11 @@ static void tcp_reinit_congestion_contro icsk->icsk_ca_setsockopt = 1; memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
+ if (ca->flags & TCP_CONG_NEEDS_ECN) + INET_ECN_xmit(sk); + else + INET_ECN_dontxmit(sk); + if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))) tcp_init_congestion_control(sk); }