linux-kernel - Re: [tip:locking/core] locking/refcount: Create unchecked atomic

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Date:   Mon, 4 Sep 2017 21:35:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        Manfred Spraul <manfred@...orfullife.com>,
        Rik van Riel <riel@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Eric Biggers <ebiggers3@...il.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        David Windsor <dwindsor@...il.com>,
        Ingo Molnar <mingo@...nel.org>, Jann Horn <jannh@...gle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-arch <linux-arch@...r.kernel.org>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:locking/core] locking/refcount: Create unchecked atomic_t
 implementation

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@...radead.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.