Re: [PATCH v2 net] tcp: fix mid stream window clamp.

[Eric Dumazet <edumazet@google.com>]

On Mon, Dec 4, 2023 at 5:08 PM Paolo Abeni <pabeni@redhat.com> wrote:
>
> After the blamed commit below, if the user-space application performs
> window clamping when tp->rcv_wnd is 0, the TCP socket will never be
> able to announce a non 0 receive window, even after completely emptying
> the receive buffer and re-setting the window clamp to higher values.
>
> Refactor tcp_set_window_clamp() to address the issue: when the user
> decreases the current clamp value, set rcv_ssthresh according to the
> same logic used at buffer initialization, but ensuring reserved mem
> provisioning.
>
> To avoid code duplication factor-out the relevant bits from
> tcp_adjust_rcv_ssthresh() in a new helper and reuse it in the above
> scenario.
>
> When increasing the clamp value, give the rcv_ssthresh a chance to grow
> according to previously implemented heuristic.
>
> Fixes: 3aa7857fe1d7 ("tcp: enable mid stream window clamp")
> Reported-by: David Gibson <david@gibson.dropbear.id.au>
> Reported-by: Stefano Brivio <sbrivio@redhat.com>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>