linux-kernel - Re: [PATCH v2 03/36] mm: use do_futex() instead of sys_futex() in mm

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Date:   Fri, 16 Mar 2018 11:43:48 -0700
From:   Darren Hart <dvhart@...radead.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        viro@...iv.linux.org.uk, luto@...nel.org, mingo@...nel.org,
        akpm@...ux-foundation.org, arnd@...db.de,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 03/36] mm: use do_futex() instead of sys_futex() in
 mm_release()

On Thu, Mar 15, 2018 at 08:04:56PM +0100, Dominik Brodowski wrote:
> sys_futex() is a wrapper to do_futex() which does not modify any
> values here:
> 
> - uaddr, val and val3 are kept the same
> 
> - op is masked with FUTEX_CMD_MASK, but is always set to FUTEX_WAKE.
>   Therefore, val2 is always 0.
> 
> - as utime is set to NULL, *timeout is NULL
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Darren Hart <dvhart@...radead.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>

Hi Dominik,

I'm missing the "why" part here. What is it you are trying to address?

do_futex is not currently in use outside of the futex implementation,
while sys_futex is. This decouples the interface from the
implementation. While this is perhaps less critical within the
kernel, I don't see a compelling reason to increase the coupling
between the mm and futex implementations.

Without a compelling WHY, Nack from me.

-- 
Darren Hart
VMware Open Source Technology Center