netdev - Re: [Patch net-next 2/2] net: dump whole skb data in netdev_rx_csum

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Message-ID: <CAF=yD-+zQv7xB4vKkgb919uAeg9VJ5VyJnC1_5NiS4PGFLyFRA@mail.gmail.com>
Date:   Thu, 10 Jan 2019 19:20:14 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Peter Oskolkov <posk.devel@...il.com>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [Patch net-next 2/2] net: dump whole skb data in netdev_rx_csum_fault()

On Wed, Dec 5, 2018 at 12:33 PM Peter Oskolkov <posk.devel@...il.com> wrote:
>
> FWIW, I find the patch really useful - I applied it to my local dev
> repo (with minor changes) and use skb_dump() a lot now. It would be
> great if it makes its way into net-next in some form.

+1 very informative.

skb_warn_bad_offload would also benefit from more packet detail.

And please consider logging device info, too. I'm currently debugging
a (non-reproducible so far, so relying purely on the log message) stack
trace for a packet that triggers that warning in validate_xmit_skb on the
path to an unknown virtual device.





> On Fri, Nov 30, 2018 at 12:15 PM Saeed Mahameed <saeedm@...lanox.com> wrote:
> >
> > On Thu, 2018-11-22 at 17:45 -0800, Cong Wang wrote:
> > > On Wed, Nov 21, 2018 at 11:33 AM Saeed Mahameed <saeedm@...lanox.com>
> > > wrote:
> > > > On Wed, 2018-11-21 at 10:26 -0800, Eric Dumazet wrote:
> > > > > On Wed, Nov 21, 2018 at 10:17 AM Cong Wang <
> > > > > xiyou.wangcong@...il.com>
> > > > > wrote:
> > > > > > On Wed, Nov 21, 2018 at 5:05 AM Eric Dumazet <
> > > > > > eric.dumazet@...il.com> wrote:
> > > > > > >
> > > > > > > On 11/20/2018 06:13 PM, Cong Wang wrote:
> > > > > > > > Currently, we only dump a few selected skb fields in
> > > > > > > > netdev_rx_csum_fault(). It is not suffient for debugging
> > > > > > > > checksum
> > > > > > > > fault. This patch introduces skb_dump() which dumps skb mac
> > > > > > > > header,
> > > > > > > > network header and its whole skb->data too.
> > > > > > > >
> > > > > > > > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > > > > > > > Cc: Eric Dumazet <edumazet@...gle.com>
> > > > > > > > Cc: David Miller <davem@...emloft.net>
> > > > > > > > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > > > > > > > ---
> > > > > > > > +     print_hex_dump(level, "skb data: ",
> > > > > > > > DUMP_PREFIX_OFFSET,
> > > > > > > > 16, 1,
> > > > > > > > +                    skb->data, skb->len, false);
> > > > > > >
> > > > > > > As I mentioned to David, we want all the bytes that were
> > > > > > > maybe
> > > > > > > already pulled
> > > > > > >
> > > > > > > (skb->head starting point, not skb->data)
> > > > > >
> > > > > > Hmm, with mac header and network header, it is effectively from
> > > > > > skb->head, no?
> > > > > > Is there anything between skb->head and mac header?
> > > > >
> > > > > Oh, I guess we wanted a single hex dump, or we need some user
> > > > > program
> > > > > to be able to
> > > > > rebuild from different memory zones the original
> > > > > CHECKSUM_COMPLETE
> > > > > value.
> > > > >
> > > >
> > > > Normally the driver keeps some headroom @skb->head, so the actual
> > > > mac
> > > > header starts @ skb->head + driver_specific_headroom
> > >
> > > Good to know, but this headroom isn't covered by skb->csum, so
> > > not useful here, right? The skb->csum for mlx5 only covers network
> > > header and its payload.
> >
> > correct
> >