s390/smp: Avoid busy loop after halt and "begin" on z/VM

Currently the smp_stop_cpu() function for SMP kernels enters a busy
loop when "begin" is entered on the z/VM console after Linux is halted.
To avoid this behavior, use the non-SMP variant of smp_stop_cpu()
which stops the CPU again after "begin" is entered. As a side
effect we now have consistent behavior for SMP and non-SMP Linux.
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/smp.h

@@ -30,7 +30,6 @@ extern int smp_store_status(int cpu);
 extern int smp_vcpu_scheduled(int cpu);
 extern void smp_yield_cpu(int cpu);
 extern void smp_yield(void);
-extern void smp_stop_cpu(void);
 extern void smp_cpu_set_polarization(int cpu, int val);
 extern int smp_cpu_get_polarization(int cpu);
 extern void smp_fill_possible_mask(void);
@@ -54,6 +53,8 @@ static inline void smp_yield_cpu(int cpu) { }
 static inline void smp_yield(void) { }
 static inline void smp_fill_possible_mask(void) { }
 
+#endif /* CONFIG_SMP */
+
 static inline void smp_stop_cpu(void)
 {
 	u16 pcpu = stap();
@@ -64,8 +65,6 @@ static inline void smp_stop_cpu(void)
 	}
 }
 
-#endif /* CONFIG_SMP */
-
 #ifdef CONFIG_HOTPLUG_CPU
 extern int smp_rescan_cpus(void);
 extern void __noreturn cpu_die(void);

arch/s390/kernel/smp.c

@@ -404,15 +404,6 @@ void smp_send_stop(void)
 	}
 }
 
-/*
- * Stop the current cpu.
- */
-void smp_stop_cpu(void)
-{
-	pcpu_sigp_retry(pcpu_devices + smp_processor_id(), SIGP_STOP, 0);
-	for (;;) ;
-}
-
 /*
  * This is the main routine where commands issued by other
  * cpus are handled.