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Date:	Sun, 05 Sep 2010 09:49:43 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Plamen Petrov <pvp-lsts@...uni-ruse.bg>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum_dev

Le samedi 04 septembre 2010 à 22:34 +0200, Jarek Poplawski a écrit :

> Hi again,
> 
> Just had a second look, and unless I miss something...
> 
> Plamen, could you test this patch, too? (Without removing the previous
> one.)
> 
> Thanks,
> Jarek P.
> 
> ------------------->
> 
> [PATCH] gro: Re-fix different skb headrooms
> 
> The patch: "gro: fix different skb headrooms" in its part:
> "2) allocate a minimal skb for head of frag_list" is buggy. The copied
> skb has p->data set at the ip header at the moment, and skb_gro_offset
> is the length of ip + tcp headers. So, after the change the length of
> mac header is skipped. Later skb_set_mac_header() sets it into the
> NET_SKB_PAD area (if it's long enough) and ip header is misaligned at
> NET_SKB_PAD + NET_IP_ALIGN offset. There is no reason to assume the
> original skb was wrongly allocated, so let's copy it as it was.
> 
> bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=16626
> fixes commit: 3d3be4333fdf6faa080947b331a6a19bce1a4f57
> 
> Reported-by: Plamen Petrov <pvp-lsts@...uni-ruse.bg>
> Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
> CC: Eric Dumazet <eric.dumazet@...il.com>
> ---
> 
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 26396ff..c83b421 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -2706,7 +2706,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
>  	} else if (skb_gro_len(p) != pinfo->gso_size)
>  		return -E2BIG;
>  
> -	headroom = NET_SKB_PAD + NET_IP_ALIGN;
> +	headroom = skb_headroom(p);
>  	nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC);
>  	if (unlikely(!nskb))
>  		return -ENOMEM;

You are right, thanks for reviewing this patch again :)

By the way, NET_IP_ALIGN is now 0 on x86, so technically speaking, your
patch un-aligns IP header on x86, but thats OK, since other arches might
want it being aligned, while x86 doesnt care.

Acked-by: Eric Dumazet <eric.dumazet@...il.com>



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