On Fri, 20 Nov 2020 19:47:44 -0800 Alexander Duyck wrote:
> From: Alexander Duyck <alexanderduyck@xxxxxx>
>
> When a BPF program is used to select between a type of TCP congestion
> control algorithm that uses either ECN or not there is a case where the
> synack for the frame was coming up without the ECT0 bit set. A bit of
> research found that this was due to the final socket being configured to
> dctcp while the listener socket was staying in cubic.
>
> To reproduce it all that is needed is to monitor TCP traffic while running
> the sample bpf program "samples/bpf/tcp_cong_kern.c". What is observed,
> assuming tcp_dctcp module is loaded or compiled in and the traffic matches
> the rules in the sample file, is that for all frames with the exception of
> the synack the ECT0 bit is set.
>
> To address that it is necessary to make one additional call to
> tcp_bpf_ca_needs_ecn using the request socket and then use the output of
> that to set the ECT0 bit for the tos/tclass of the packet.
>
> Fixes: 91b5b21c7c16 ("bpf: Add support for changing congestion control")
> Signed-off-by: Alexander Duyck <alexanderduyck@xxxxxx>
Applied, thank you!
