When running refscale as a module, any ref_scale_init() issues will be
reflected in the error code from modprobe or insmod, as the case may be.
However, these error codes are not available when running refscale
built-in, for example, when using the kvm.sh script.  This commit
therefore adds WARN_ON_ONCE() to allow distinguishing ref_scale_init()
errors when running refscale built-in.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
                init_waitqueue_head(&shutdown_wq);
                firsterr = torture_create_kthread(ref_scale_shutdown, NULL,
                                                  shutdown_task);
-               if (firsterr)
+               if (torture_init_error(firsterr))
                        goto unwind;
                schedule_timeout_uninterruptible(1);
        }
        for (i = 0; i < nreaders; i++) {
                firsterr = torture_create_kthread(ref_scale_reader, (void *)i,
                                                  reader_tasks[i].task);
-               if (firsterr)
+               if (torture_init_error(firsterr))
                        goto unwind;
 
                init_waitqueue_head(&(reader_tasks[i].wq));
        // Main Task
        init_waitqueue_head(&main_wq);
        firsterr = torture_create_kthread(main_func, NULL, main_task);
-       if (firsterr)
+       if (torture_init_error(firsterr))
                goto unwind;
 
        torture_init_end();