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Date: Mon, 4 Sep 2017 21:35:27 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [tip:locking/core] locking/refcount: Create unchecked atomic_t
 implementation
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To: Kees Cook <keescook@chromium.org>
Cc: "David S. Miller" <davem@davemloft.net>, Arnd Bergmann <arnd@arndb.de>, Manfred Spraul <manfred@colorfullife.com>, Rik van Riel <riel@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Eric Biggers <ebiggers3@gmail.com>, "Reshetova, Elena" <elena.reshetova@intel.com>, David Windsor <dwindsor@gmail.com>, Ingo Molnar <mingo@kernel.org>, Jann Horn <jannh@google.com>, "Serge E. Hallyn" <serge@hallyn.com>, Alexey Dobriyan <adobriyan@gmail.com>, Greg KH <gregkh@linuxfoundation.org>, "Eric W. Biederman" <ebiederm@xmission.com>, Hans Liljestrand <ishkamiel@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Christoph Hellwig <hch@infradead.org>, Josh Poimboeuf <jpoimboe@redhat.com>, LKML <linux-kernel@vger.kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Davidlohr Bueso <dave@stgolabs.net>, linux-arch <linux-arch@vger.kernel.org>, James Bottomley <James.Bottomley@hansenpartnership.com>, "linux-tip-commits@vger.kernel.org" <linux-tip-commits@vger.kernel.org>
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On Mon, Sep 04, 2017 at 10:11:37AM -0700, Kees Cook wrote:
> On Mon, Sep 4, 2017 at 5:37 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Wed, Jun 28, 2017 at 09:58:15AM -0700, tip-bot for Kees Cook wrote:
> >> locking/refcount: Create unchecked atomic_t implementation
> >
> > This seems to do only half the job. Here's the rest.
> >
> > ---
> > Subject: locking/refcount: Finish unchecked atomic_t implementation
> >
> > For some reason the unchecked atomic_t implementation stopped half-way
> > through, complete it it.
> 
> Hmm? The reason is that the implementation of the remaining functions
> is unchanged between full, unchecked, and x86.

But they're wasted code if !arch because the existing atomic functions
are adequate (and I would argue better in case of atomic_add_unless).

And arch implementations would certainly want to reimplement dec_not_one.

Plus, you completely failed mention any of this.