Recursion on the free page queue mutex occurred when UMA needed to allocate a new page of radix trie nodes to complete a vm_radix_insert() operation that was requested by vm_page_cache(). vm_page_cache() already held the free page queue lock when UMA tried to acquire it through its call to vm_page_alloc(). This code path no longer exists, so there is no reason to allow recursion on the free page queue mutex.