netdev - Re: Resurrecting due to huge ipoib perf regression - [BUG] skb corruption and kernel panic at forwarding with fragmentation

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Date:	Fri, 8 Jul 2016 14:17:31 -0700
From:	Roland Dreier <roland@...estorage.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Alexander Duyck <alexander.duyck@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	Florian Westphal <fw@...len.de>,
	Thadeu Lima de Souza Cascardo <cascardo@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Resurrecting due to huge ipoib perf regression - [BUG] skb
 corruption and kernel panic at forwarding with fragmentation

On Fri, Jul 8, 2016 at 9:51 AM, Jason Gunthorpe
<jgunthorpe@...idianresearch.com> wrote:
> So, it appears, the dst and neigh can be used for all performances cases.
>
> For the non performance dst == null case, can we just burn cycles and
> stuff the daddr in front of the packet at hardheader time, even if we
> have to copy?

OK, sounds interesting.

Unfortunately the scope of this work has gotten to the point where I
can't take it on right now.  My system is running 4.4.y for now
(before struct skb_gso_cb grew) so I think shrinking struct skb_gso_cb
to 8 bytes plus changing SKB_SGO_CB_OFFSET to 20 will work for now.
Hope someone is able to come up with a real fix before I need to
upgrade to 4.10.y...

 - R.