[S390] smp/idle: call init_idle() before starting a new cpu

Call init_idle() which (re-)initializes the idle task structure before
it gets used on a new cpu.
That way we can also get rid of the odd preempt_enable_no_resched()
call we have in the cpu offline path within cpu_idle(). That call
prevented preempt count imbalances between cpu hotplug operations.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/smp.h

@@ -20,7 +20,6 @@ extern void machine_power_off_smp(void);
 
 extern int __cpu_disable (void);
 extern void __cpu_die (unsigned int cpu);
-extern void cpu_die (void) __attribute__ ((noreturn));
 extern int __cpu_up (unsigned int cpu);
 
 extern struct mutex smp_cpu_state_mutex;
@@ -71,8 +70,10 @@ static inline void smp_switch_to_ipl_cpu(void (*func)(void *), void *data)
 
 #ifdef CONFIG_HOTPLUG_CPU
 extern int smp_rescan_cpus(void);
+extern void __noreturn cpu_die(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/process.c

@@ -42,6 +42,7 @@
 #include <asm/irq.h>
 #include <asm/timer.h>
 #include <asm/nmi.h>
+#include <asm/smp.h>
 #include "entry.h"
 
 asmlinkage void ret_from_fork(void) asm ("ret_from_fork");
@@ -76,13 +77,8 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
  */
 static void default_idle(void)
 {
-	/* CPU is going idle. */
-#ifdef CONFIG_HOTPLUG_CPU
-	if (cpu_is_offline(smp_processor_id())) {
-		preempt_enable_no_resched();
+	if (cpu_is_offline(smp_processor_id()))
 		cpu_die();
-	}
-#endif
 	local_irq_disable();
 	if (need_resched()) {
 		local_irq_enable();

arch/s390/kernel/smp.c

@@ -575,6 +575,7 @@ int __cpuinit __cpu_up(unsigned int cpu)
 		idle = c_idle.idle;
 		current_set[cpu] = c_idle.idle;
 	}
+	init_idle(idle, cpu);
 	if (smp_alloc_lowcore(cpu))
 		return -ENOMEM;
 	do {