linux-kernel - Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount

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Message-ID: <1490148199.16816.126.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 21 Mar 2017 19:03:19 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Miller <davem@...emloft.net>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Network Development <netdev@...r.kernel.org>,
        bridge@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Patrick McHardy <kaber@...sh.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to
 refcount_t

On Tue, 2017-03-21 at 16:51 -0700, Kees Cook wrote:

> Am I understanding you correctly that you'd want something like:
> 
> refcount.h:
> #ifdef UNPROTECTED_REFCOUNT
> #define refcount_inc(x)   atomic_inc(x)
> ...
> #else
> void refcount_inc(...
> ...
> #endif
> 
> some/net.c:
> #define UNPROTECTED_REFCOUNT
> #include <refcount.h>
> 
> or similar?

At first, it could be something simple like that yes.

Note that we might define two refcount_inc()  : One that does whole
tests, and refcount_inc_relaxed() that might translate to atomic_inc()
on non debug kernels.

Then later, maybe provide a dynamic infrastructure so that we can
dynamically force the full checks even for refcount_inc_relaxed() on say
1% of the hosts, to get better debug coverage ?