netdev - Re: [Xen-devel] [PATCH] xen-netfront: pull on receive skb may need to happen earlier

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Message-Id: <51DBCF4F02000078000E3793@nat28.tlf.novell.com>
Date:	Tue, 09 Jul 2013 07:52:31 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Wei Liu" <wei.liu2@...rix.com>
Cc:	"Ian Campbell" <ian.campbell@...rix.com>, <davem@...emloft.net>,
	"Dion Kant" <g.w.kant@...enet.nl>, <xen-devel@...ts.xen.org>,
	<netdev@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen-netfront: pull on receive skb may
 need to happen earlier

>>> On 08.07.13 at 17:48, Wei Liu <wei.liu2@...rix.com> wrote:
> On Mon, Jul 08, 2013 at 03:20:26PM +0100, Jan Beulich wrote:
>> @@ -1014,7 +1025,7 @@ err:
>>  
>>  		skb_shinfo(skb)->frags[0].page_offset = rx->offset;
>>  		skb_frag_size_set(&skb_shinfo(skb)->frags[0], rx->status);
>> -		skb->data_len = rx->status;
>> +		skb->len = skb->data_len = rx->status;
> 
> This is not correct. You should not be needing this. Now you lose count
> of SKB head len. Try to go without the above line and see if it makes a
> difference?

I don't follow - at this point, there's 0 bytes of head (this only
changes with the first call to __pskb_pull_tail()). Hence ->len ==
->data_len seems correct to me (and afaict pulling would do the
wrong thing if I dropped that change).

Jan

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