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Date:	Wed, 2 Oct 2013 10:58:42 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org,
	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	kaber@...sh.net, herbert@...dor.apana.org.au,
	eric.dumazet@...il.com
Subject: Re: [PATCH] ipv6: udp packets following an UFO enqueued packet need
 also be handled by UFO

Wed, Oct 02, 2013 at 01:25:34AM CEST, hannes@...essinduktion.org wrote:
>On Tue, Oct 01, 2013 at 11:47:21PM +0200, Hannes Frederic Sowa wrote:
>> The strange thing is that if I don't do the IPV6_MTU setsockopt I don't
>> get an oops.
>
>This is incorrect, it just depends on the size of the writes and on the
>interface mtu.
>
>> IPv4 seems to work without problems, too.
>
>I also get kernel oopses from IPv4 now, too.
>
>
>So, skb_is_gso is not accurate enough in the output and we have to check if we
>already started to append to skb frags. The following diff does resolve this
>issue in both the IPv4 and IPv6 non-page-append output path but I am not
>confident if it is correct:
>
>diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>index 6d56840..3565450 100644
>--- a/include/linux/skbuff.h
>+++ b/include/linux/skbuff.h
>@@ -1308,6 +1308,11 @@ static inline int skb_pagelen(const struct sk_buff *skb)
> 	return len + skb_headlen(skb);
> }
> 
>+static inline bool skb_has_frags(const struct sk_buff *skb)
>+{
>+	return skb_shinfo(skb)->nr_frags;
>+}
>+
> /**
>  * __skb_fill_page_desc - initialise a paged fragment in an skb
>  * @skb: buffer containing fragment to be initialised
>diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>index 7d8357b..8dc3d8d 100644
>--- a/net/ipv4/ip_output.c
>+++ b/net/ipv4/ip_output.c
>@@ -836,7 +836,7 @@ static int __ip_append_data(struct sock *sk,
> 		csummode = CHECKSUM_PARTIAL;
> 
> 	cork->length += length;
>-	if (((length > mtu) || (skb && skb_is_gso(skb))) &&
>+	if (((length > mtu) || (skb && skb_has_frags(skb))) &&
> 	    (sk->sk_protocol == IPPROTO_UDP) &&
> 	    (rt->dst.dev->features & NETIF_F_UFO) && !rt->dst.header_len) {
> 		err = ip_ufo_append_data(sk, queue, getfrag, from, length,
>diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>index a54c45c..ded4f6f 100644
>--- a/net/ipv6/ip6_output.c
>+++ b/net/ipv6/ip6_output.c
>@@ -1227,7 +1227,7 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
> 	skb = skb_peek_tail(&sk->sk_write_queue);
> 	cork->length += length;
> 	if (((length > mtu) ||
>-	     (skb && skb_is_gso(skb))) &&
>+	     (skb && skb_has_frags(skb))) &&
> 	    (sk->sk_protocol == IPPROTO_UDP) &&
> 	    (rt->dst.dev->features & NETIF_F_UFO)) {
> 		err = ip6_ufo_append_data(sk, getfrag, from, length,
>
>Greetings,
>
>  Hannes
>


This seems correct to me. sk_is_gso would work as well is you apply my
patch "[patch net] ip6_output: do skb ufo init for peeked non ufo skb as
well" which does the setting of gso_size.

Jiri
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