netdev - Re: [RFC net PATCH] virtio_net: disable XDP_REDIRECT in receive

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Date:   Sun, 18 Feb 2018 15:22:04 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>, brouer@...hat.com,
        Björn Töpel <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>
Subject: Re: [RFC net PATCH] virtio_net: disable XDP_REDIRECT in
 receive_mergeable() case

On Fri, 16 Feb 2018 13:31:37 +0800 Jason Wang <jasowang@...hat.com> wrote:

> > Besides the described bug:
> >
> > Update(1): There is also a OOM leak in the XDP_REDIRECT code, which
> > receive_small() is likely also affected by.

Found the issue behind this memory leak... page refcnt issues when
hitting xmit error paths.

> > Update(2): Also observed a guest crash when redirecting out an
> > another virtio_net device, when device is down.  

Also found reason behind this. It is not related to a "down" device.
It caused by redirect into a virtio_net device that does not have setup
sufficient XDP TX queues (which it assumes is one per CPU). I have a
preliminary fix patch.

> Will have a look at these issues. (Holiday in china now, so will do it 
> after).

No worry.  I can take care of this... I'll cleanup my patches and test
them Monday, should have patches ready Tuesday... as I want to make
sure they work in all the different error cases.

I'll be working on improvements for the XDP_REDIRECT code paths anyway
next week... in preparations for supporting the AF_XDP use case.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer