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Date:   Fri, 16 Mar 2018 11:43:48 -0700
From:   Darren Hart <dvhart@infradead.org>
To:     Dominik Brodowski <linux@dominikbrodowski.net>
Cc:     linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
        viro@zeniv.linux.org.uk, luto@kernel.org, mingo@kernel.org,
        akpm@linux-foundation.org, arnd@arndb.de,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 03/36] mm: use do_futex() instead of sys_futex() in
 mm_release()
Message-ID: <20180316184348.GA20184@localhost.localdomain>
References: <20180315190529.20943-1-linux@dominikbrodowski.net>
 <20180315190529.20943-4-linux@dominikbrodowski.net>
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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@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Darren Hart <dvhart@infradead.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.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