linux-kernel - Re: [PATCH v2] refcount: Create unchecked atomic

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Date:   Wed, 7 Jun 2017 23:58:09 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jann Horn <jannh@...gle.com>,
        Eric Biggers <ebiggers3@...il.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, arozansk@...hat.com,
        Davidlohr Bueso <dave@...olabs.net>,
        Manfred Spraul <manfred@...orfullife.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>,
        Rik van Riel <riel@...hat.com>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v2] refcount: Create unchecked atomic_t implementation

On Wed, Jun 07, 2017 at 07:58:31PM -0700, Kees Cook wrote:
> Many subsystems will not use refcount_t unless there is a way to build the
> kernel so that there is no regression in speed compared to atomic_t. This
> adds CONFIG_REFCOUNT_FULL to enable the full refcount_t implementation
> which has the validation but is slightly slower. When not enabled,
> refcount_t uses the basic unchecked atomic_t routines, which results in
> no code changes compared to just using atomic_t directly.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> This is v2 of this patch, which I've split from the arch-specific
> alternative implementation for x86. Getting this patch in will unblock
> atomic_t -> refcount_t conversion, and the x86 alternative implementation
> can be developed in parallel. Changes from v1: use better atomic ops,
> thanks to Elena and Peter.

Yeah, can we get this in ASAP?  Without having to always incur the over
this will allow us to convert subsystems to refcount_t broadly.