I don't think it is a clear way to fix this. If someone want to
use PADATA in a non-SMP system, he should be carefully to handle
the non-SMP case himself. I think the better way is to make PADATA
handle the non-SMP case, I think it should be easy for it, which
could just call ->thread_fn() many times instead of creating many
threads in the non-SMP case.
Thanks.