Re: [PATCH] mptcp: push queued data on passive TFO subflows becoming established

[T S Rameshkumar]

Hi Petar, Matthieu, Mat,

Thanks for the feedback and confirmation!

Indeed, since the bug predates e00b63056fb4 and exists back to when server-side
Fast Open was originally introduced, the appropriate Fixes tag would be:

Fixes: fb7084501a61 ("mptcp: add support for TCP_FASTOPEN sockopt")

During our testing with simulated network latency in namespaces, we also found
that when the 3rd ACK arrives:
1. check_fully_established() marks subflow->fully_established = true.
2. But within tcp_ack(), the underlying TCP state is still TCP_SYN_RECV until
   tcp_rcv_state_process() sets it to TCP_ESTABLISHED.
3. Therefore, invoking the push in subflow_state_change() ensures the subflow
   is recognized as active by __tcp_can_send() and immediately flushes the
   queued write buffer.

I can send a [PATCH net v2] with the updated Fixes tag once maintainers review.

Thanks,
T S Rameshkumar