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Date: Thu, 4 Dec 2014 14:06:57 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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        Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH RFC] locking: Add volatile to arch_spinlock_t structures
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On Thu, Dec 04, 2014 at 09:45:46PM +0000, One Thousand Gnomes wrote:
> > anywhere in that translation unit.  After all, any non-static function
> > in that translation unit might be called from some other translation
> > unit that -did- use locking or whatever.
> > 
> > I will let you know how it goes.  ;-)
> 
> It breaks DEC10 ;-)

To say nothing of CDC 6600 systems lacking the compare-move unit.  ;-)

> If there is kickback over things like optimisation perhaps the gcc
> maintainers could at least consider something like
> 
> 	int __attribute((threadsafe)) fred;
> 
> ??

Not needed for recent gcc versions -- both the C11 and C++11 standards
require that different threads be permitted to independently access
different variables, where "different" means "no bits of the two variables
residing in the same byte".  From what I can see, this would mean that
a conforming pre-EV56 Alpha C11 compiler would need to use LDL_L and
STL_C to carry out 8-bit and 16-bit stores.  ;-)

							Thanx, Paul