linux-kernel - Re: [RFC][PATCH 2/7] kref: Add kref

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Message-ID: <20161121160059.GB3174@twins.programming.kicks-ass.net>
Date:   Mon, 21 Nov 2016 17:00:59 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
Cc:     David Windsor <dwindsor@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [RFC][PATCH 2/7] kref: Add kref_read()

On Mon, Nov 21, 2016 at 04:49:15PM +0100, Peter Zijlstra wrote:
> > Speaking of non-fitting patterns. This one is quite common in
> > networking code for refcounters:
> > 
> > if (atomic_cmpxchg(&cur->refcnt, 1, 0) == 1) {} This is from
> > net/netfilter/nfnetlink_acct.c, but there are similar ones in other
> > places.
> 
> Cute, but weird it doesn't actually decrement if not 1.

Hurgh.. creative refcounting that. The question is how much of that do
we want to support? It really must not decrement there.