netdev - Re: [Bug 209423] WARN_ON_ONCE() at rtl8169_tso_csum

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Date:   Fri, 2 Oct 2020 10:46:07 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [Bug 209423] WARN_ON_ONCE() at rtl8169_tso_csum_v2()

On Fri, Oct 2, 2020 at 10:32 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 10/2/20 10:26 AM, Eric Dumazet wrote:
> > On Thu, Oct 1, 2020 at 10:34 PM Heiner Kallweit <hkallweit1@...il.com> wrote:
> >>
> >> I have a problem with the following code in ndo_start_xmit() of
> >> the r8169 driver. A user reported the WARN being triggered due
> >> to gso_size > 0 and gso_type = 0. The chip supports TSO(6).
> >> The driver is widely used, therefore I'd expect much more such
> >> reports if it should be a common problem. Not sure what's special.
> >> My primary question: Is it a valid use case that gso_size is
> >> greater than 0, and no SKB_GSO_ flag is set?
> >> Any hint would be appreciated.
> >>
> >>
> >
> > Maybe this is not a TCP packet ? But in this case GSO should have taken place.
> >
> > You might add a
> > pr_err_once("gso_type=%x\n", shinfo->gso_type);
> >

>
> Ah, sorry I see you already printed gso_type
>
> Must then be a bug somewhere :/


napi_reuse_skb() does :

skb_shinfo(skb)->gso_type = 0;

It does _not_ clear gso_size.

I wonder if in some cases we could reuse an skb while gso_size is not zero.

Normally, we set it only from dev_gro_receive() when the skb is queued
into GRO engine (status being GRO_HELD)