netdev - Re: [PATCH net-next 1/5] net: add support for noref skb->sk

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Message-ID: <1505929295.29839.103.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 20 Sep 2017 10:41:35 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net-next 1/5] net: add support for noref skb->sk

On Wed, 2017-09-20 at 18:54 +0200, Paolo Abeni wrote:
> Noref sk do not carry a socket refcount, are valid
> only inside the current RCU section and must be
> explicitly cleared before exiting such section.
> 
> They will be used in a later patch to allow early demux
> without sock refcounting.




> +/* dummy destructor used by noref sockets */
> +void sock_dummyfree(struct sk_buff *skb)
> +{

BUG();

> +}
> +EXPORT_SYMBOL(sock_dummyfree);
> +


I do not see how you ensure we do not leave RCU section with an skb
destructor pointing to this sock_dummyfree()

This patch series looks quite dangerous to me.

Do we really have real applications using connected UDP sockets and
wanting very high pps throughput ?

I am pretty sure the bottleneck is the sender part.