[RFC] [PATCH] powerpc: Fix missing barriers in atomic_exchange_and_add_{acq,rel}

[Torvald Riegel]

On Tue, 2014-10-21 at 21:54 +0200, Torvald Riegel wrote:
> On powerpc, atomic_exchange_and_add is implemented without any barriers.
> However, atomic_exchange_and_add_acq and atomic_exchange_and_add_rel
> (which supposedly should have acquire / release barrier semantics) both
> fall back to atomic_exchange_and_add if they are not defined (see
> include/atomic.h).  I have not reviewed existing code to see whether
> this would indeed cause a bug, but this lack of barriers likely is a
> (future) fault, and prevents any use of
> atomic_exchange_and_add_{acq,rel} that actually rely on the barrier
> semantics.  Therefore, this patch defines
> atomic_exchange_and_add_{acq,rel} using atomic_read_barrier /
> atomic_write_barrier.
> 
> I have NOT tested this.  Can somebody who cares about powerpc please
> have a look and test this?  Thanks!

Ping.