Re: PV DomU running linux 3.17.3 causing xen-netback fatal error in Dom0

[Anthony Wright <anthony@overnetdata.com>]

On 08/12/2014 12:03, David Vrabel wrote:
> Does this patch to netfront fix it?
>
> 8<---------------------------------------------
> xen-netfront: use correct linear area after linearizing an skb
>
> Commit 97a6d1bb2b658ac85ed88205ccd1ab809899884d (xen-netfront: Fix
> handling packets on compound pages with skb_linearize) attempted to
> fix a problem where an skb that would have required too many slots
> would be dropped causing TCP connections to stall.
>
> However, it filled in the first slot using the original buffer and not
> the new one and would use the wrong offset and grant access to the
> wrong page.
>
> Netback would notice the malformed request and stop all traffic on the
> VIF, reporting:
>
>     vif vif-3-0 vif3.0: txreq.offset: 85e, size: 4002, end: 6144
>     vif vif-3-0 vif3.0: fatal error; disabling device
>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
>  drivers/net/xen-netfront.c |    3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index ece8d18..eeed0ce 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -627,6 +627,9 @@ static int xennet_start_xmit(struct sk_buff *skb,
> struct net_device *dev)
>  				    slots, skb->len);
>  		if (skb_linearize(skb))
>  			goto drop;
> +		data = skb->data;
> +		offset = offset_in_page(data);
> +		len = skb_headlen(skb);
>  	}
>
>  	spin_lock_irqsave(&queue->tx_lock, flags);
The patch seems to have worked. Before we'd managed to reproduce the
problem in under 10 seconds, with the patch we haven't seen the problem
on the test or production systems.

Thank you.

Anthony.