netdev - Re: [PATCH v2] net: Require exact match for TCP socket lookups if dif is l3mdev

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Date:   Fri, 14 Oct 2016 06:21:19 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH v2] net: Require exact match for TCP socket lookups if dif
 is l3mdev

On 10/14/16 12:33 AM, Eric Dumazet wrote:
> There is a catch here.
> TCP moves IP6CB() in a different location.
> 
> Reference :
> 
> 971f10eca186 ("tcp: better TCP_SKB_CB layout to reduce cache line misses")

thanks for the reference.


> Problem is that the lookup can happen from IP early demux, before TCP
> moved IP{6}CB around.

For TCP we only need the exact_dif match for listen sockets, so early demux does not apply.

> 
> So you might need to let the caller pass IP6CB(skb)->flags (or
> TCP_SKB_CB(skb)->header.h6.flags ) instead of skb since
> inet6_exact_dif_match() does not know where to fetch the flags.
> 
> Same issue for IPv4.

I'll update the match functions to pull from TCP_SKB_CB instead of IP6CB and make a note of the above.

Thanks for the review