netdev - Re: [patch 2/2] [PATCH] qeth: l3 hw tx csum circumvent hw bug

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Date:	Sat, 15 Jan 2011 20:46:25 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	frank.blaschka@...ibm.com
Cc:	netdev@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [patch 2/2] [PATCH] qeth: l3 hw tx csum circumvent hw bug

From: Frank Blaschka <frank.blaschka@...ibm.com>
Date: Thu, 13 Jan 2011 09:23:59 +0100

> On Wed, Jan 12, 2011 at 11:47:35PM -0800, David Miller wrote:
>> From: frank.blaschka@...ibm.com
>> Date: Thu, 13 Jan 2011 07:42:25 +0100
>> 
>> > --- a/drivers/s390/net/qeth_l3_main.c
>> > +++ b/drivers/s390/net/qeth_l3_main.c
>> > @@ -2998,7 +2998,9 @@ static inline void qeth_l3_hdr_csum(stru
>> >  	 */
>> >  	if (iph->protocol == IPPROTO_UDP)
>> >  		hdr->hdr.l3.ext_flags |= QETH_HDR_EXT_UDP;
>> > -	hdr->hdr.l3.ext_flags |= QETH_HDR_EXT_CSUM_TRANSP_REQ;
>> > +	hdr->hdr.l3.ext_flags |= QETH_HDR_EXT_CSUM_TRANSP_REQ |
>> > +		QETH_HDR_EXT_CSUM_HDR_REQ;
>> > +	iph->check = 0;
>> >  	if (card->options.performance_stats)
>> >  		card->perf_stats.tx_csum++;
>> >  }
>> 
>> You may not change the packet header contents blindly like this.
>> Otherwise unpredictable contents will be seen by tcpdump and any
>> other code path which has a clone of this packet.
>> 
>> Thus, you'll need to guard this change with something like:
>> 
>> 		if (skb_header_cloned(skb) &&
>> 		    pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) {
>> 			dev_kfree_skb(skb);
>> 			goto tx_fail;
>> 		}
> Yes I know. Because of the suboptimal l3 driver design :-) we already have
> a private copy of the skb at this place. Thx!

I see, thanks for explaining.

Both patches applied, thanks.
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