Quite ugly, IMHO: rhashtable_insert_fast() may return -ENOMEM as non-permanent error, if allocation in GFP_ATOMIC failed. In this case, allocation in GFP_KERNEL is retried by rht_deferred_worker(). Sadly, there is no way to determine if that has already been tried and failed. The thread test triggers GFP_ATOMIC allocation failure quite easily, so I can't really just ignore this issue. :)