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

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Date:   Sun, 11 Apr 2021 13:37:10 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eric Dumazet <edumazet@...gle.com>
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 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.

Guenter