netdev - Re: [PATCH net] virtio_net: Do not pull payload in skb->head

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Message-ID: <CANn89iJa8KAnfWvUB8Jr8hsG5x_Amg90DbpoAHiuNZigv75MEA@mail.gmail.com>
Date:   Sun, 11 Apr 2021 23:23:20 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net] virtio_net: Do not pull payload in skb->head

On Sun, Apr 11, 2021 at 10:37 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 4/11/21 8:06 AM, Eric Dumazet wrote:
> > On Sun, Apr 11, 2021 at 3:43 PM Guenter Roeck <linux@...ck-us.net> wrote:
> >
> >> This patch causes a virtio-net interface failure when booting sh4 images
> >> in qemu. The test case is nothing special: Just try to get an IP address
> >> using udhcpc. If it fails, udhcpc reports:
> >>
> >> udhcpc: started, v1.33.0
> >> udhcpc: sending discover
> >> FAIL
> >>
> >
> > Can you investigate where the incoming packet is dropped ?
> >
>
> Unless I am missing something, packets are not dropped. It looks more
> like udhcpc gets bad indigestion in the receive path and exits immediately.
> Plus, it doesn't happen all the time; sometimes it receives the discover
> response and is able to obtain an IP address.
>
> Overall this is quite puzzling since udhcpc exits immediately when the problem
> is seen, no matter which option I give it on the command line; it should not
> really do that.


Could you strace both cases and report differences you can spot ?

strace -o STRACE -f -s 1000 udhcpc