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 <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/include/asm/smp.h

···
 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);
···
 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();
···
 		cpu_relax();
 	}
 }
-
-#endif /* CONFIG_SMP */
 
 #ifdef CONFIG_HOTPLUG_CPU
 extern int smp_rescan_cpus(void);

arch/s390/kernel/smp.c

···
 }
 
 /*
- * 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.
  */