From: Andi Kleen <ak@suse.de>
To: Linus Torvalds <torvalds@osdl.org>, rth@redhat.com
Subject: Re: [patch] i386: make bitops safe
Date: Tue, 28 Feb 2006 00:47:22 +0100
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Cc: Chuck Ebbert <76306.1226@compuserve.com>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>
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On Tuesday 28 February 2006 00:06, Linus Torvalds wrote:
> On Mon, 27 Feb 2006, Chuck Ebbert wrote:
> > Make i386 bitops safe.  Currently they can be fooled, even on
> > uniprocessor, by code that uses regions of the bitmap before
> > invoking the bitop.  The least costly way to make them safe
> > is to add a memory clobber and tag all of them as volatile.
>
> Actually, the least costly way should be to make the "ADDR" define work
> right again.
>
> It used to do something magic like

I remember asking rth about this at some point and IIRC
he expressed doubts if it would actually do what expected. Richard?

-Andi

>
> 	struct fake_area {
> 		unsigned long members[1000];
> 	};
>
> 	#define ADDR (*(volatile struct fake_area *)addr)
>
> which was correct. I forget why it got broken into using just a "long *"
> (it happened a long long time ago).
>
> 		Linus
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