linux-kernel - Re: [tip:locking/core] refcount_t: Introduce a special purpose refcount type

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Message-ID: <CAGXu5jJFa9cW-YQtDqyckfiDxJrfd1FOa3eoQAwOrvmtnOeqLA@mail.gmail.com>
Date:   Mon, 13 Feb 2017 09:48:42 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        David Windsor <dwindsor@...il.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>
Subject: Re: [tip:locking/core] refcount_t: Introduce a special purpose
 refcount type

On Mon, Feb 13, 2017 at 6:34 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Feb 10, 2017 at 12:31:15AM -0800, tip-bot for Peter Zijlstra wrote:
>> Commit-ID:  f405df5de3170c00e5c54f8b7cf4766044a032ba
>> Gitweb:     http://git.kernel.org/tip/f405df5de3170c00e5c54f8b7cf4766044a032ba
>> Author:     Peter Zijlstra <peterz@...radead.org>
>> AuthorDate: Mon, 14 Nov 2016 18:06:19 +0100
>> Committer:  Ingo Molnar <mingo@...nel.org>
>> CommitDate: Fri, 10 Feb 2017 09:04:19 +0100
>>
>> refcount_t: Introduce a special purpose refcount type
>>
>> Provide refcount_t, an atomic_t like primitive built just for
>> refcounting.
>>
>> It provides saturation semantics such that overflow becomes impossible
>> and thereby 'spurious' use-after-free is avoided.
>>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>
> ---
> Subject: refcount: Out-of-line everything
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Fri Feb 10 16:27:52 CET 2017
>
> Linus asked to please make this real C code.

No objection from me, but I'm curious to see the conversation. Where
did this discussion happen? (I'm curious to see the reasoning behind
the decisions about the various trade-offs.)

> And since size then isn't an issue what so ever anymore, remove the
> debug knob and make all WARN()s unconditional.

Are you still going to land the x86 WARN_ON improvements?

-Kees

-- 
Kees Cook
Pixel Security