netdev - Re: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum

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Date:	Wed, 08 Sep 2010 07:57:31 +0300
From:	Plamen Petrov <pvp-lsts@...uni-ruse.bg>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Jarek Poplawski <jarkao2@...il.com>,
	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

На 05.9.2010 г. 10:49, Eric Dumazet написа:
> 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>
>
>
>

Well, now that I'm back at work, I'm glad to report
that I tested both variants of the patch, and as Eric
points out - it works both ways.

So, which ever fits you guys better.

Thanks a lot!
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