Date: Thu, 8 Jun 2017 13:09:31 -0700
From: Davidlohr Bueso <dave@stgolabs.net>
To: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>, Jann Horn <jannh@google.com>,
        Eric Biggers <ebiggers3@gmail.com>,
        Hans Liljestrand <ishkamiel@gmail.com>,
        David Windsor <dwindsor@gmail.com>,
        Greg KH <gregkh@linuxfoundation.org>, Ingo Molnar <mingo@redhat.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        "arozansk@redhat.com" <arozansk@redhat.com>,
        Manfred Spraul <manfred@colorfullife.com>,
        "axboe@kernel.dk" <axboe@kernel.dk>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        "x86@kernel.org" <x86@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, "David S. Miller" <davem@davemloft.net>,
        Rik van Riel <riel@redhat.com>,
        linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH v2] refcount: Create unchecked atomic_t implementation
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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@chromium.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