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Date:   Mon, 21 Dec 2020 20:04:45 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Ben Greear <greearb@...delatech.com>,
        Rainer Suhm <automat@...teo.de>
Cc:     Johannes Berg <johannes@...solutions.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Luca Coelho <luciano.coelho@...el.com>,
        netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: net: tso: add UDP segmentation support: adds regression for ax200 upload

On Mon, Dec 21, 2020 at 7:46 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Sat, Dec 19, 2020 at 5:55 PM Ben Greear <greearb@...delatech.com> wrote:
> >
> > On 12/19/20 7:18 AM, Johannes Berg wrote:
> > > On Fri, 2020-12-18 at 12:16 -0800, Jakub Kicinski wrote:
> > >> On Thu, 17 Dec 2020 12:40:26 -0800 Ben Greear wrote:
> > >>> On 12/17/20 10:20 AM, Eric Dumazet wrote:
> > >>>> On Thu, Dec 17, 2020 at 7:13 PM Ben Greear <greearb@...delatech.com> wrote:
> > >>>>> It is the iwlwifi/mvm logic that supports ax200.
> > >>>>
> > >>>> Let me ask again :
> > >>>>
> > >>>> I see two different potential call points :
> > >>>>
> > >>>> drivers/net/wireless/intel/iwlwifi/pcie/tx.c:1529:
> > >>>> tso_build_hdr(skb, hdr_page->pos, &tso, data_left, !total_len);
> > >>>> drivers/net/wireless/intel/iwlwifi/queue/tx.c:427:
> > >>>> tso_build_hdr(skb, hdr_page->pos, &tso, data_left, !total_len);
> > >>>>
> > >>>> To the best of your knowledge, which one would be used in your case ?
> > >>>>
> > >>>> Both are horribly complex, I do not want to spend time studying two
> > >>>> implementations.
> > >>>
> > >>> It is the queue/tx.c code that executes on my system, verified with
> > >>> printk.
> > >>
> > >> Not sure why Intel's not on CC here.
> > >
> > > Heh :)
> > >
> > > Let's also add linux-wireless.
> > >
> > >> Luca, is the ax200 TSO performance regression with recent kernel on your
> > >> radar?
> > >
> > > It wasn't on mine for sure, so far. But it's supposed to be Christmas
> > > vacation, so haven't checked our bug tracker etc. I see Emmanuel was at
> > > least looking at the bug report, but not sure what else happened yet.
> >
> > Not to bitch and moan too much, but even the most basic of testing would
> > have shown this, how can testing be so poor on the ax200 driver?
> >
> > It even shows up with the out-of-tree ax200 driver.
> >
> > > Off the top of my head, I don't really see the issue. Does anyone have
> > > the ability to capture the frames over the air (e.g. with another AX200
> > > in monitor mode, load the driver with amsdu_size=3 module parameter to
> > > properly capture A-MSDUs)?
> >
> > I can do that at some point, and likely it could be reproduced with an /n or /ac
> > AP and those are a lot easier to sniff.
> >
> > Thanks,
> > Ben
> >
> >
> > --
> > Ben Greear <greearb@...delatech.com>
> > Candela Technologies Inc  http://www.candelatech.com
>
> It seems the problem comes from some skbs reaching the driver with
> gso_type == 0,
> meaning skb_is_gso_tcp() is fuzzy. (net/core/tso.c is only one of the
> skb_is_gso_tcp() users)
>
> Local TCP stack should provide either SKB_GSO_TCPV4 or SKB_GSO_TCPV6
> for GSO packets.
>
> So maybe the issue is coming from traffic coming from a VM through a
> tun device or something,
> and our handling of GSO_ROBUST / DODGY never cared about setting
> SKB_GSO_TCPV4 or SKB_GSO_TCPV6 if not already given by user space ?
>
> Or a plain bug somewhere, possibly overwriting  gso_type with 0 or garbage...

Oh well, iwl_mvm_tx_tso_segment() 'builds' a fake gso packet.

I suspect this will fix the issue :

diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/tx.c
b/drivers/net/wireless/intel/iwlwifi/mvm/tx.c
index a983c215df310776ffe67f3b3ffa203eab609bfc..e7ad6367c88de4aff700c630d850760d1d3bf011
100644
--- a/drivers/net/wireless/intel/iwlwifi/mvm/tx.c
+++ b/drivers/net/wireless/intel/iwlwifi/mvm/tx.c
@@ -773,6 +773,7 @@ iwl_mvm_tx_tso_segment(struct sk_buff *skb,
unsigned int num_subframes,

        next = skb_gso_segment(skb, netdev_flags);
        skb_shinfo(skb)->gso_size = mss;
+       skb_shinfo(skb)->gso_type = ipv4 ? SKB_GSO_TCPV4 : SKB_GSO_TCPV6;
        if (WARN_ON_ONCE(IS_ERR(next)))
                return -EINVAL;
        else if (next)

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