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

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Date:   Thu, 8 Jun 2017 13:09:31 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.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>,
        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" <arozansk@...hat.com>,
        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 Thu, 08 Jun 2017, Reshetova, Elena wrote:

>> 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.
>
>+1. If this gets in, I can refresh the rest of the patches in net, mm, ipc, block, etc. and send them for review again.

Yes, this would be a prerequisite for ipc; which I initially thought didn't
take a performance hit.

Thanks,
Davidlohr