Merge branch 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull SMP fix from Thomas Gleixner:
 "Replace the bogus BUG_ON in the cpu hotplug code"

* 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  smp/hotplug: Replace BUG_ON and react useful

kernel/cpu.c

@@ -279,7 +279,8 @@ static int bringup_wait_for_ap(unsigned int cpu)
 
 	/* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
 	wait_for_completion(&st->done);
-	BUG_ON(!cpu_online(cpu));
+	if (WARN_ON_ONCE((!cpu_online(cpu))))
+		return -ECANCELED;
 
 	/* Unpark the stopper thread and the hotplug thread of the target cpu */
 	stop_machine_unpark(cpu);