slab, workqueue: remove keventd_up() usage

Now that workqueue can handle work item queueing from very early
during boot, there is no need to gate schedule_delayed_work_on() while
!keventd_up().  Remove it.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org

mm/slab.c

@@ -550,12 +550,7 @@ static void start_cpu_timer(int cpu)
 {
 	struct delayed_work *reap_work = &per_cpu(slab_reap_work, cpu);
 
-	/*
-	 * When this gets called from do_initcalls via cpucache_init(),
-	 * init_workqueues() has already run, so keventd will be setup
-	 * at that time.
-	 */
-	if (keventd_up() && reap_work->work.func == NULL) {
+	if (reap_work->work.func == NULL) {
 		init_reap_node(cpu);
 		INIT_DEFERRABLE_WORK(reap_work, cache_reap);
 		schedule_delayed_work_on(cpu, reap_work,