s390: Use generic idle thread allocation

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20120420124557.652574928@linutronix.de

arch/s390/Kconfig

@@ -122,6 +122,7 @@ config S390
 	select ARCH_INLINE_WRITE_UNLOCK_BH
 	select ARCH_INLINE_WRITE_UNLOCK_IRQ
 	select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
+	select GENERIC_SMP_IDLE_THREAD
 
 config SCHED_OMIT_FRAME_POINTER
 	def_bool y

arch/s390/kernel/smp.c

@@ -85,7 +85,6 @@ enum {
 
 struct pcpu {
 	struct cpu cpu;
-	struct task_struct *idle;	/* idle process for the cpu */
 	struct _lowcore *lowcore;	/* lowcore page(s) for the cpu */
 	unsigned long async_stack;	/* async stack for the cpu */
 	unsigned long panic_stack;	/* panic stack for the cpu */
@@ -721,26 +720,9 @@ static void __cpuinit smp_start_secondary(void *cpuvoid)
 	cpu_idle();
 }
 
-struct create_idle {
-	struct work_struct work;
-	struct task_struct *idle;
-	struct completion done;
-	int cpu;
-};
-
-static void __cpuinit smp_fork_idle(struct work_struct *work)
-{
-	struct create_idle *c_idle;
-
-	c_idle = container_of(work, struct create_idle, work);
-	c_idle->idle = fork_idle(c_idle->cpu);
-	complete(&c_idle->done);
-}
-
 /* Upping and downing of CPUs */
 int __cpuinit __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
-	struct create_idle c_idle;
 	struct pcpu *pcpu;
 	int rc;
 
@@ -750,22 +732,12 @@ int __cpuinit __cpu_up(unsigned int cpu, struct task_struct *tidle)
 	if (pcpu_sigp_retry(pcpu, sigp_initial_cpu_reset, 0) !=
 	    sigp_order_code_accepted)
 		return -EIO;
-	if (!pcpu->idle) {
-		c_idle.done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done);
-		INIT_WORK_ONSTACK(&c_idle.work, smp_fork_idle);
-		c_idle.cpu = cpu;
-		schedule_work(&c_idle.work);
-		wait_for_completion(&c_idle.done);
-		if (IS_ERR(c_idle.idle))
-			return PTR_ERR(c_idle.idle);
-		pcpu->idle = c_idle.idle;
-	}
-	init_idle(pcpu->idle, cpu);
+
 	rc = pcpu_alloc_lowcore(pcpu, cpu);
 	if (rc)
 		return rc;
 	pcpu_prepare_secondary(pcpu, cpu);
-	pcpu_attach_task(pcpu, pcpu->idle);
+	pcpu_attach_task(pcpu, tidle);
 	pcpu_start_fn(pcpu, smp_start_secondary, NULL);
 	while (!cpu_online(cpu))
 		cpu_relax();
@@ -852,7 +824,6 @@ void __init smp_prepare_boot_cpu(void)
 	struct pcpu *pcpu = pcpu_devices;
 
 	boot_cpu_address = stap();
-	pcpu->idle = current;
 	pcpu->state = CPU_STATE_CONFIGURED;
 	pcpu->address = boot_cpu_address;
 	pcpu->lowcore = (struct _lowcore *)(unsigned long) store_prefix();