netdev - Re: [PATCH v2 1/1] xen/netback: correctly calculate required slots of skb.

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Date:	Tue, 16 Jul 2013 10:00:47 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	David Miller <davem@...emloft.net>
CC:	<annie.li@...cle.com>, <xen-devel@...ts.xensource.com>,
	<netdev@...r.kernel.org>, <wei.liu2@...rix.com>,
	<konrad.wilk@...cle.com>, <msw@...zon.com>
Subject: Re: [PATCH v2 1/1] xen/netback: correctly calculate required slots
 of skb.

On Thu, 2013-07-11 at 13:03 -0700, David Miller wrote:
> From: Annie Li <annie.li@...cle.com>
> Date: Wed, 10 Jul 2013 17:15:11 +0800
> 
> > When counting required slots for skb, netback directly uses DIV_ROUND_UP to get
> > slots required by header data. This is wrong when offset in the page of header
> > data is not zero, and is also inconsistent with following calculation for
> > required slot in netbk_gop_skb.
> > 
> > In netbk_gop_skb, required slots are calculated based on offset and len in page
> > of header data. It is possible that required slots here is larger than the one
> > calculated in earlier netbk_count_requests. This inconsistency directly results
> > in rx_req_cons_peek and xen_netbk_rx_ring_full judgement are wrong.
> > 
> > Then it comes to situation the ring is actually full, but netback thinks it is
> > not and continues to create responses. This results in response overlaps request
> > in the ring, then grantcopy gets wrong grant reference and throws out error,
> > for example "(XEN) grant_table.c:1763:d0 Bad grant reference 2949120", the
> > grant reference is invalid value here. Netback returns XEN_NETIF_RSP_ERROR(-1)
> > to netfront when grant copy status is error, then netfront gets rx->status
> > (the status is -1, not really data size now), and throws out error,
> > "kernel: net eth1: rx->offset: 0, size: 4294967295". This issue can be reproduced
> > by doing gzip/gunzip in nfs share with mtu = 9000, the guest would panic after
> > running such test for a while.
> > 
> > This patch is based on 3.10-rc7.
> > 
> > Signed-off-by: Annie Li <annie.li@...cle.com>
> 
> A lot of discussion... will we have another respin of this patch or can I
> get an ACK from Ian or someone else?

I was out at a conference last week and I'm heading off again for
another on Saturday. I need to go back through this thread and the
alternative from Matt and figure out what is what. I hope to get to it
in the back half of this week, or perhaps in some airport somewhere :-/.

Sorry for the delay.

Ian.

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