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Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber

From Pranith Kumar <bobby.prani@gmail.com>
Newsgroups linux.kernel
Subject Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber
Date 2015-10-06 22:30 +0200
Message-ID <qgH22-8u5-9@gated-at.bofh.it> (permalink)
References <qgFCW-6fq-9@gated-at.bofh.it> <qgGSn-8hZ-27@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Tue, Oct 6, 2015 at 4:16 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>
> NAK.  We already have the "+m" for exactly this reason; adding an
> explicit memory clobber should only be used to prevent movement of
> *other* memory operations around this one (i.e. a barrier).
>

OK. If that is so, can you please explain why we need it in the
__raw_cmpxchg() case? I think it is a good idea to make cmpxchg() and
cmpxchg_double() have similar barrier semantics.

Thanks!
-- 
Pranith
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[PATCH] x86: cmpxchg_double: Add missing memory clobber Pranith Kumar <bobby.prani@gmail.com> - 2015-10-06 21:00 +0200
  Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber "H. Peter Anvin" <hpa@zytor.com> - 2015-10-06 22:20 +0200
    Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber Pranith Kumar <bobby.prani@gmail.com> - 2015-10-06 22:30 +0200
      Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber "H. Peter Anvin" <hpa@zytor.com> - 2015-10-06 23:40 +0200
        Re: [PATCH] x86: cmpxchg_double: Add missing memory clobber Peter Zijlstra <peterz@infradead.org> - 2015-10-07 15:10 +0200

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