netdev - Re: Is it a possible bug in dev_gro

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Message-ID: <20100802102906.GA8439@ff.dom.local>
Date:	Mon, 2 Aug 2010 10:29:06 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Xin Xiaohui <xiaohui.xin@...el.com>
Cc:	netdev@...r.kernel.org, herbert@...dor.apana.org.au,
	davem@...emloft.net
Subject: Re: Is it a possible bug in dev_gro_receive()?

Xin Xiaohui wrote:
> I looked into the code dev_gro_receive(), found the code here:
> if the frags[0] is pulled to 0, then the page will be released,
> and memmove() frags left.
> Is that right? I'm not sure if memmove do right or not, but
> frags[0].size is never set after memove at least. what I think
> a simple way is not to do anything if we found frags[0].size == 0.
> The patch is as followed.
> 
> Or am I missing something here?

I think, you're right, but fixing memmove looks nicer to me:

 -	--skb_shinfo(skb)->nr_frags);
 +	--skb_shinfo(skb)->nr_frags * sizeof(skb_frag_t));

Jarek P.

> 
> ---
>  net/core/dev.c |    7 -------
>  1 files changed, 0 insertions(+), 7 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 264137f..28cdbbf 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2730,13 +2730,6 @@ pull:
>  
>  		skb_shinfo(skb)->frags[0].page_offset += grow;
>  		skb_shinfo(skb)->frags[0].size -= grow;
> -
> -		if (unlikely(!skb_shinfo(skb)->frags[0].size)) {
> -			put_page(skb_shinfo(skb)->frags[0].page);
> -			memmove(skb_shinfo(skb)->frags,
> -				skb_shinfo(skb)->frags + 1,
> -				--skb_shinfo(skb)->nr_frags);
> -		}
>  	}
>  
>  ok:



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