netdev - Re: Linux 5.12-rc7

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Date:   Mon, 12 Apr 2021 18:31:25 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: Linux 5.12-rc7

On Mon, Apr 12, 2021 at 6:28 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Sun, Apr 11, 2021 at 10:14 PM Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > Qemu test results:
> >         total: 460 pass: 459 fail: 1
> > Failed tests:
> >         sh:rts7751r2dplus_defconfig:ata:net,virtio-net:rootfs
> >
> > The failure bisects to commit 0f6925b3e8da ("virtio_net: Do not pull payload in
> > skb->head"). It is a spurious problem - the test passes roughly every other
> > time. When the failure is seen, udhcpc fails to get an IP address and aborts
> > with SIGTERM. So far I have only seen this with the "sh" architecture.
>
> Hmm. Let's add in some more of the people involved in that commit, and
> also netdev.
>
> Nothing in there looks like it should have any interaction with
> architecture, so that "it happens on sh" sounds odd, but maybe it's
> some particular interaction with the qemu environment.

Yes, maybe.

I spent few hours on this, and suspect a buggy memcpy() implementation
on SH, but this was not conclusive.

By pulling one extra byte, the problem goes away.

Strange thing is that the udhcpc process does not go past sendto().