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

[Wei Liu <liuw@xxxxxxxxx>]

On Thu, Jul 11, 2013 at 9:03 PM, David Miller <davem@xxxxxxxxxxxxx> wrote:
> From: Annie Li <annie.li@xxxxxxxxxx>
> 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@xxxxxxxxxx>
>
> A lot of discussion... will we have another respin of this patch or can I
> get an ACK from Ian or someone else?
>

Matt also proposed a solution to this issue ([PATCH RFC] xen-netback: calculate
the number of slots required for large MTU vifs -- it's posted on netdev as
well).

We're discussing these two patches at the moment and have not come to a
conclusion on which one to go in. I would really appreciate if you could wait a
little longer. Thanks.


Wei.

> Thanks.
>
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