netdev - Re: [PATCH net v2] udp: preserve skb->dst if required for IP options processing

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Message-Id: <20170718.120040.847904052360889957.davem@davemloft.net>
Date:   Tue, 18 Jul 2017 12:00:40 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com,
        hannes@...essinduktion.org
Subject: Re: [PATCH net v2] udp: preserve skb->dst if required for IP
 options processing

From: Paolo Abeni <pabeni@...hat.com>
Date: Tue, 18 Jul 2017 11:57:55 +0200

> Eric noticed that in udp_recvmsg() we still need to access
> skb->dst while processing the IP options.
> Since commit 0a463c78d25b ("udp: avoid a cache miss on dequeue")
> skb->dst is no more available at recvmsg() time and bad things
> will happen if we enter the relevant code path.
> 
> This commit address the issue, avoid clearing skb->dst if
> any IP options are present into the relevant skb.
> Since the IP CB is contained in the first skb cacheline, we can
> test it to decide to leverage the consume_stateless_skb()
> optimization, without measurable additional cost in the faster
> path.
> 
> v1 -> v2: updated commit message tags
> 
> Fixes: 0a463c78d25b ("udp: avoid a cache miss on dequeue")
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Reported-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Applied, thank you.