netdev - Re: TCP stall issue

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Message-Id: <32E2B684-5D8C-41E3-B17A-938A5F784461@gmail.com>
Date:   Fri, 26 Feb 2021 17:26:03 +0100
From:   Gil Pedersen <kanongil@...il.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Neal Cardwell <ncardwell@...gle.com>,
        David Miller <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: TCP stall issue

> On 26 Feb 2021, at 15.39, David Laight <David.Laight@...LAB.COM> wrote:
> 
> Some thoughts...
> 
> Does a non-android linux system behave correctly through the same NAT gateways?
> Particularly with a similar kernel version.
> 
> If you have a USB OTG cable and USB ethernet dongle you may be able to get
> android to use a wired ethernet connection - excluding any WiFi issues.
> (OTG usually works for keyboard and mouse, dunno if ethernet support is there.)
> 
> Does you android device work on any other networks?

I have done some further tests. I managed to find another Android device (kernel 4.9.113), which thankfully does _not_ send the weird D-SACKs and quickly recovers, so the problem appears to be on the original device.

Additionally, I have managed to do a trace on the WLAN AP, where I can confirm that all packets seem to be transferred without unnecessary modifications or re-ordering. Ie. all segments sent from the server make it to the device and any loss will be device local. As such this points to a driver-level issue?

I don't have an ethernet dongle ready. I tried to connect using cellular and was unable to replicate the issue, so this further points at a driver-level issue.

Given that it now seems relevant, the device is an Android P20 Lite, running a variant of Android 9.1 with an update from this year (kernel was built jan. 05 2021).

/Gil