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Date: Tue, 26 Apr 2016 18:11:07 +0200
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Rich Felker <dalias@libc.org>
Cc: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Davidlohr Bueso <dave@stgolabs.net>, Ingo Molnar <mingo@kernel.org>,
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        Geert Uytterhoeven <geert@linux-m68k.org>,
        Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH] futex: fix shared futex operations on nommu
Message-ID: <20160426161107.GF8295@linutronix.de>
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* Rich Felker | 2016-04-26 11:53:44 [-0400]:

>The whole shared futex logic is meaningless for nommu. Perhaps I
>should have written a better message, though.
>
>With MMU, shared futex keys need to identify the physical backing for
>a memory address because it may be mapped at different addresses in
>different processes (or even multiple times in the same process).
>Without MMU this cannot happen. You only have physical addresses. So
>the "private futex" behavior of using the virtual address as the key
>is always correct (for both shared and private cases) on nommu
>systems.

So using a shared futex on NOMMU does work but it would be more
efficient to always use a private futex instead.
Is this what you are saying?

>Rich

Sebastian