Peter Zijlstra <[email protected]> wrote:
> Basically we fail for:
>
> *x = 1;
> atomic_inc(u);
> smp_mb__after_atomic();
> r0 = *y;
>
> Because, while the atomic_inc() implies memory order, it
> (surprisingly) does not provide a compiler barrier. This then allows
> the compiler to re-order like so:
To quote memory-barriers.txt:
(*) smp_mb__before_atomic();
(*) smp_mb__after_atomic();
These are for use with atomic (such as add, subtract, increment and
decrement) functions that don't return a value, especially when used for
reference counting. These functions do not imply memory barriers.
so it's entirely to be expected?
David
