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

David Miller
2011-01-16T04:46:25Z

From: Frank Blaschka <frank.blaschka@de.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@de.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.