On Wed, Mar 19, 2014 at 07:47:52AM +0100, Peter Zijlstra wrote:
> As per the existing implementation; implement the new one using
> smp_mb().
>
> AFAICT the s390 compare-and-swap does imply a barrier, however there
> are some immediate ops that seem to be singly-copy atomic and do not
> imply a barrier. One such is the "ni" op (which would be
> and-immediate) which is used for the constant clear_bit
> implementation. Therefore s390 needs full barriers for the
> {before,after} atomic ops.
That is correct... and made me look again into the recent bitops and
atomic changes I made.
Looks like I missed to add some mandatory memory barriers. Oh well.
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