s390: enforce CONFIG_HOTPLUG_CPU

x86 and powerpc (partially) enforce already CONFIG_HOTPLUG_CPU. On
s390 it is enabled on all distributions by default since ages.
The only exception is our zfcpdump kernel.

However to simplify testing, enforce HOTPLUG_CPU. This was suggested
by Paul McKenney, since his rcutorture test environments for CONFIG_SMP=y
only support HOTPLUG_CPU=y.
Suggested-by: NPaul E. McKenney <paulmck@linux.ibm.com>
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/Kconfig

@@ -413,11 +413,6 @@ config NR_CPUS
 
 config HOTPLUG_CPU
 	def_bool y
-	prompt "Support for hot-pluggable CPUs"
-	help
-	  Say Y here to be able to turn CPUs off and on. CPUs
-	  can be controlled through /sys/devices/system/cpu/cpu#.
-	  Say N if you want to disable CPU hotplug.
 
 # Some NUMA nodes have memory ranges that span
 # other nodes.	Even though a pfn is valid and

arch/s390/include/asm/smp.h

@@ -53,14 +53,9 @@ static inline int smp_get_base_cpu(int cpu)
 	return cpu - (cpu % (smp_cpu_mtid + 1));
 }
 
-#ifdef CONFIG_HOTPLUG_CPU
 extern int smp_rescan_cpus(void);
 extern void __noreturn cpu_die(void);
 extern void __cpu_die(unsigned int cpu);
 extern int __cpu_disable(void);
-#else
-static inline int smp_rescan_cpus(void) { return 0; }
-static inline void cpu_die(void) { }
-#endif
 
 #endif /* __ASM_SMP_H */

arch/s390/kernel/smp.c

@@ -232,8 +232,6 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
 	return -ENOMEM;
 }
 
-#ifdef CONFIG_HOTPLUG_CPU
-
 static void pcpu_free_lowcore(struct pcpu *pcpu)
 {
 	unsigned long async_stack, nodat_stack, lowcore;
@@ -253,8 +251,6 @@ static void pcpu_free_lowcore(struct pcpu *pcpu)
 	free_pages(lowcore, LC_ORDER);
 }
 
-#endif /* CONFIG_HOTPLUG_CPU */
-
 static void pcpu_prepare_secondary(struct pcpu *pcpu, int cpu)
 {
 	struct lowcore *lc = pcpu->lowcore;
@@ -895,8 +891,6 @@ static int __init _setup_possible_cpus(char *s)
 }
 early_param("possible_cpus", _setup_possible_cpus);
 
-#ifdef CONFIG_HOTPLUG_CPU
-
 int __cpu_disable(void)
 {
 	unsigned long cregs[16];
@@ -937,8 +931,6 @@ void __noreturn cpu_die(void)
 	for (;;) ;
 }
 
-#endif /* CONFIG_HOTPLUG_CPU */
-
 void __init smp_fill_possible_mask(void)
 {
 	unsigned int possible, sclp_max, cpu;
@@ -996,7 +988,6 @@ int setup_profiling_timer(unsigned int multiplier)
 	return 0;
 }
 
-#ifdef CONFIG_HOTPLUG_CPU
 static ssize_t cpu_configure_show(struct device *dev,
 				  struct device_attribute *attr, char *buf)
 {
@@ -1073,7 +1064,6 @@ static ssize_t cpu_configure_store(struct device *dev,
 	return rc ? rc : count;
 }
 static DEVICE_ATTR(configure, 0644, cpu_configure_show, cpu_configure_store);
-#endif /* CONFIG_HOTPLUG_CPU */
 
 static ssize_t show_cpu_address(struct device *dev,
 				struct device_attribute *attr, char *buf)
@@ -1083,9 +1073,7 @@ static ssize_t show_cpu_address(struct device *dev,
 static DEVICE_ATTR(address, 0444, show_cpu_address, NULL);
 
 static struct attribute *cpu_common_attrs[] = {
-#ifdef CONFIG_HOTPLUG_CPU
 	&dev_attr_configure.attr,
-#endif
 	&dev_attr_address.attr,
 	NULL,
 };
@@ -1144,15 +1132,11 @@ static int smp_add_present_cpu(int cpu)
 out_topology:
 	sysfs_remove_group(&s->kobj, &cpu_common_attr_group);
 out_cpu:
-#ifdef CONFIG_HOTPLUG_CPU
 	unregister_cpu(c);
-#endif
 out:
 	return rc;
 }
 
-#ifdef CONFIG_HOTPLUG_CPU
-
 int __ref smp_rescan_cpus(void)
 {
 	struct sclp_core_info *info;
@@ -1188,17 +1172,14 @@ static ssize_t __ref rescan_store(struct device *dev,
 	return rc ? rc : count;
 }
 static DEVICE_ATTR_WO(rescan);
-#endif /* CONFIG_HOTPLUG_CPU */
 
 static int __init s390_smp_init(void)
 {
 	int cpu, rc = 0;
 
-#ifdef CONFIG_HOTPLUG_CPU
 	rc = device_create_file(cpu_subsys.dev_root, &dev_attr_rescan);
 	if (rc)
 		return rc;
-#endif
 	for_each_present_cpu(cpu) {
 		rc = smp_add_present_cpu(cpu);
 		if (rc)