fix bogus hotplug cpu warning

Fix bogus DEBUG_PREEMPT warning on x86_64, when cpu brought online after
bootup: current_is_keventd is right to note its use of smp_processor_id
is preempt-safe, but should use raw_smp_processor_id to avoid the warning.
Signed-off-by: NHugh Dickins <hugh@veritas.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/workqueue.c

@@ -635,7 +635,7 @@ int keventd_up(void)
 int current_is_keventd(void)
 {
 	struct cpu_workqueue_struct *cwq;
-	int cpu = smp_processor_id();	/* preempt-safe: keventd is per-cpu */
+	int cpu = raw_smp_processor_id(); /* preempt-safe: keventd is per-cpu */
 	int ret = 0;
 
 	BUG_ON(!keventd_wq);