Re: [Xen-devel] Bug in hash changes to netback in 4.7.2 kernel

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Anthony Wright [mailto:anthony@xxxxxxxxxxxxxxx]
> Sent: 06 September 2016 14:37
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Xen-devel <xen-
> devel@xxxxxxxxxxxxx>
> Subject: Re: Bug in hash changes to netback in 4.7.2 kernel
> 
> On 06/09/2016 13:57, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Anthony Wright [mailto:anthony@xxxxxxxxxxxxxxx]
> >> Sent: 06 September 2016 13:23
> >> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
> >> Cc: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> >> Subject: Bug in hash changes to netback in 4.7.2 kernel
> >>
> >> When I run Xen (4.7.0) nested in VirtualBox (5.0.24_Ubuntu r108355)
> >> with a
> >> linux-4.7.2 Dom0 kernel, none of my DomU's (linux-3.17.3) have
> >> network connectivity because they reject all packets with the error
> 'Invalid extra type:
> >> 4'. When I run exactly the same setup on bare metal, I don't get the
> >> error messages.
> >>
> >> From poking around in the code this seems to be because the 4.7.2
> >> kernel wrongly decides that the DomU's will understand
> >> EXTRA_TYPE_HASH, and so attach it to the network packet. Since the
> >> DomU's don't understand the extra info their netfront driver rejects the
> whole packet.
> > The code in xenvif_select_queue() deliberately clears the skb->sw_hash
> field (which gates adding the new extra type) if the hash algorithm selected
> by the frontend is 'none', which should be the default. So, unless you have a
> frontend that is implementing the control ring protocol, but failing to
> recognize the new extra type I'm not how you're seeing the problem...
> unless somehow a packet which hash is getting into netback's start_xmit
> without first having gone through select_queue?
> I very much doubt that the frontend is implementing the control ring
> protocol, the DomUs are running stock linux-3.17.3. I build the system from
> source, so happy to re-compile with debug code.

Well, if you could have a look to see whether the skbs have sw_hash set when 
they get into net_rx_action() that would be something, and also check whether 
xenvif_select_queue() is being properly called. I'll take a look and see if I 
can repro this myself when I get some time.

  Paul

  
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