netdev - Re: [PATCH v2] ipv4: Early TCP socket demux.

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Message-Id: <20120620.152959.2146722628245186096.davem@davemloft.net>
Date:	Wed, 20 Jun 2012 15:29:59 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	shemminger@...tta.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2] ipv4: Early TCP socket demux.

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 20 Jun 2012 14:38:40 +0200

> Problem could happen if sk->sk_rx_dst is freed while some packets are
> still in napi or socket backlog (can happen with some network
> reordering)
> 
> 1) Socket backlog must be flushed before sk->sk_rx_dst freeing
> 
> 2) Even if we move rcu_read_lock() in net_rx_action(), we need some
> napi_gro_forcedstrefs() in case we sofnet_break
> 
> Or maybe just use napi_gro_flush() ?

Good catch, but I've just figured out a more fundamental issue
with doing this at the GRO layer.

The IPV4 input path is going to undo our early socket demux by
orphaning the SKB in ip_rcv().  So we'll end up looking up the
socket twice.
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