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Re: [PATCH] futex: fix shared futex operations on nommu

From Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Newsgroups linux.kernel
Subject Re: [PATCH] futex: fix shared futex operations on nommu
Date 2016-04-26 18:20 +0200
Message-ID <rsdSq-2bx-7@gated-at.bofh.it> (permalink)
References <rrZFL-7e1-3@gated-at.bofh.it> <rs7WI-5oQ-19@gated-at.bofh.it> <rsdz5-1JO-19@gated-at.bofh.it>
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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

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Thread

[PATCH] futex: fix shared futex operations on nommu Rich Felker <dalias@libc.org> - 2016-04-26 03:10 +0200
  Re: [PATCH] futex: fix shared futex operations on nommu Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-04-26 12:00 +0200
    Re: [PATCH] futex: fix shared futex operations on nommu Rich Felker <dalias@libc.org> - 2016-04-26 18:00 +0200
      Re: [PATCH] futex: fix shared futex operations on nommu Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-04-26 18:20 +0200
        Re: [PATCH] futex: fix shared futex operations on nommu Rich Felker <dalias@libc.org> - 2016-04-26 18:30 +0200
          Re: [PATCH] futex: fix shared futex operations on nommu Andrew Morton <akpm@linux-foundation.org> - 2016-04-27 00:30 +0200
            Re: [PATCH] futex: fix shared futex operations on nommu Rich Felker <dalias@libc.org> - 2016-04-27 00:40 +0200
  Re: [PATCH] futex: fix shared futex operations on nommu Thomas Gleixner <tglx@linutronix.de> - 2016-04-27 15:50 +0200

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