linux-kernel - Re: [PATCH 04/31] x86/mm: Introduce pte

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Message-ID: <CA+55aFxSihF0RHc8npWcMdHOo8LOx+d=aV4G6_577REn=OXsQw@mail.gmail.com>
Date:	Thu, 25 Oct 2012 13:10:27 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 04/31] x86/mm: Introduce pte_accessible()

NAK NAK NAK.

On Thu, Oct 25, 2012 at 5:16 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>
> +#define __HAVE_ARCH_PTE_ACCESSIBLE
> +static inline int pte_accessible(pte_t a)

Stop doing this f*cking crazy ad-hoc "I have some other name
available" #defines.

Use the same name, for chissake! Don't make up new random names.

Just do

   #define pte_accessible pte_accessible

and then you can use

   #ifndef pte_accessible

to define the generic thing. Instead of having this INSANE "two
different names for the same f*cking thing" crap.

Stop it. Really.

Also, this:

> +#ifndef __HAVE_ARCH_PTE_ACCESSIBLE
> +#define pte_accessible(pte)            pte_present(pte)
> +#endif

looks unsafe and like a really bad idea.

You should probably do

  #ifndef pte_accessible
    #define pte_accessible(pte) ((void)(pte),1)
  #endif

because you have no idea if other architectures do

 (a) the same trick as x86 does for PROT_NONE (I can already tell you
from a quick grep that ia64, m32r, m68k and sh do it)
 (b) might not perhaps be caching non-present pte's anyway

So NAK on this whole patch. It's bad. It's ugly, it's wrong, and it's
actively buggy.

                Linus
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