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

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Date: Tue, 5 Dec 2023 11:32:25 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Neil Spring <ntspring@...com>, 
	David Gibson <david@...son.dropbear.id.au>, Stefano Brivio <sbrivio@...hat.com>
Subject: Re: [PATCH v2 net] tcp: fix mid stream window clamp.

On Mon, Dec 4, 2023 at 5:08 PM Paolo Abeni <pabeni@...hat.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@...son.dropbear.id.au>
> Reported-by: Stefano Brivio <sbrivio@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

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