Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

[Christoph Lameter <clameter@sgi.com>]

On Fri, 17 Aug 2007, Paul E. McKenney wrote:

> On Sat, Aug 18, 2007 at 08:09:13AM +0800, Herbert Xu wrote:
> > On Fri, Aug 17, 2007 at 04:59:12PM -0700, Paul E. McKenney wrote:
> > >
> > > gcc bugzilla bug #33102, for whatever that ends up being worth.  ;-)
> > 
> > I had totally forgotten that I'd already filed that bug more
> > than six years ago until they just closed yours as a duplicate
> > of mine :)
> > 
> > Good luck in getting it fixed!
> 
> Well, just got done re-opening it for the third time.  And a local
> gcc community member advised me not to give up too easily.  But I
> must admit that I am impressed with the speed that it was identified
> as duplicate.
> 
> Should be entertaining!  ;-)

Right. ROTFL... volatile actually breaks atomic_t instead of making it 
safe. x++ becomes a register load, increment and a register store. Without 
volatile we can increment the memory directly. It seems that volatile 
requires that the variable is loaded into a register first and then 
operated upon. Understandable when you think about volatile being used to 
access memory mapped I/O registers where a RMW operation could be 
problematic.

See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3506
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