From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH] ip: reuse ip_summed of first fragment for all
 subsequent fragments
Date: Tue, 28 Dec 2010 13:49:05 -0800 (PST)
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From: Timo Juhani Lindfors <timo.lindfors@iki.fi>
Date: Mon, 20 Dec 2010 12:38:45 +0200

> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 439d2a3..c0743ed 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1167,7 +1167,7 @@ ssize_t	ip_append_page(struct sock *sk, struct page *page,
>  			/*
>  			 *	Fill in the control structures
>  			 */
> -			skb->ip_summed = CHECKSUM_NONE;
> +			skb->ip_summed = skb_prev->ip_summed;
>  			skb->csum = 0;
>  			skb_reserve(skb, hh_len);

You can't just assign skb_prev->ip_summed here, if it's CHECKSUM_PARTIAL
then things will go completely wrong.  This is especially true since
we're about to zero out skb->csum.