netdev - Re: [PATCH net-next 2/3] udp: avoid a cache miss on dequeue

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Message-ID: <1496350248.27480.19.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 01 Jun 2017 13:50:48 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 2/3] udp: avoid a cache miss on dequeue

On Thu, 2017-06-01 at 22:35 +0200, Paolo Abeni wrote:

> To make the code robust we would have to NULL all the other fields
> (nfct, nf_bridge, destructor, sk) that are currently not cleared in
> skb_release_head_state(), elsewhere if one day, after some change, any
> that fields become non-NULL in this code path we risk a double-free
> after skb_release_head_state(), even if the code looks safe.

Well, one can not predict future bugs, and we should not add code just
trying to prevent future bugs.

> 
> Will that be a little too invasive for this small use-case? Can't we
> prefer a new helper or simply a secpath_reset() plus some appropriate
> comments?

Please reuse existing functions, and amend them if needed.

Fact that we mention secpath_put() or secpath_reset() in an UDP patch
should really tell us something is wrong. This is becoming a maintenance
burden.