netdev - Re: [PATCH net-next] net/vxlan: Avoid unaligned access in vxlan_build

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Date:   Tue, 20 Sep 2016 18:43:33 +0200
From:   Jiri Benc <jbenc@...hat.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        hannes@...essinduktion.org, aduyck@...antis.com,
        daniel@...earbox.net, pabeni@...hat.com
Subject: Re: [PATCH net-next] net/vxlan: Avoid unaligned access in
 vxlan_build_skb()

On Tue, 20 Sep 2016 12:31:08 -0400, Sowmini Varadhan wrote:
> The vxlan header is after the ethernet header (14 bytes),
> IP header (20 bytes, assuming no options) and udp header (8 bytes).

If the VXLAN header is not aligned to 4 bytes, then IP header is not
aligned to 4 bytes, too, and you have greater problems than just VXLAN.

> Post the skb_reserve adjustments (see computations in in mld_newpack(),
> for example), this triggers an unaligned access on sparc.

IPv6 header is certainly not 20 bytes.

If you see unaligned access, something is wrong. But I very much doubt
that the problem is at the place you're trying to fix. Could you share
the traces with us?

 Jiri