[nginx] QUIC: do not increase underutilized congestion window.

[Vladimir Homutov]

On Tue, Apr 15, 2025 at 03:02:02PM +0000, noreply at nginx.com wrote:
> details:   https://github.com/nginx/nginx/commit/cd5e4fa1446dff86fafc3b6ffcc11afd527a024f
> branches:  master
> commit:    cd5e4fa1446dff86fafc3b6ffcc11afd527a024f
> user:      Roman Arutyunyan <arut at nginx.com>
> date:      Sat, 4 Jan 2025 18:03:46 +0400
> description:
> QUIC: do not increase underutilized congestion window.
>
> As per RFC 9002, Section 7.8, congestion window should not be increased
> when it's underutilized.
>

Hello,

it looks like this patch triggers some issues with ack processing
(possible previously, but now more probable): see details in suggested
patch.

I'm also attaching bad.log and good.log. The first one demonstrates that
nginx is not sending any ACKs since it is switched into idle mode and
the window is not increasing. Since the client code is symmetric, deadlock
occurs.