Re: [PATCH RFC] locking: Add volatile to arch_spinlock_t structures

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

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