Rather than looking at the pool of completions for spinning use an
atomic counter of total completions ever done. The relative number of
completions being waited on by rtio_submit may then always be correctly
done.
Prior to this a race was possible, and understood, as
rtio_cqe_consumable was a likely but not guaranteed count of completions.
Sure enough on an SMP system the likely count was ahead of the actual
available completions and a race was caught by the simple test case.
Signed-off-by: Tom Burdick <thomas.burdick@intel.com>
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