[ARM SMP] Track CPU idle threads

Track the idle thread task_struct for each CPU.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/smp.c

@@ -80,20 +80,24 @@ static DEFINE_SPINLOCK(smp_call_function_lock);
 
 int __cpuinit __cpu_up(unsigned int cpu)
 {
-	struct task_struct *idle;
+	struct cpuinfo_arm *ci = &per_cpu(cpu_data, cpu);
+	struct task_struct *idle = ci->idle;
 	pgd_t *pgd;
 	pmd_t *pmd;
 	int ret;
 
 	/*
-	 * Spawn a new process manually.  Grab a pointer to
-	 * its task struct so we can mess with it
+	 * Spawn a new process manually, if not already done.
+	 * Grab a pointer to its task struct so we can mess with it
 	 */
+	if (!idle) {
 		idle = fork_idle(cpu);
 		if (IS_ERR(idle)) {
 			printk(KERN_ERR "CPU%u: fork() failed\n", cpu);
 			return PTR_ERR(idle);
 		}
+		ci->idle = idle;
+	}
 
 	/*
 	 * Allocate initial page tables to allow the new CPU to
@@ -236,6 +240,8 @@ void __init smp_prepare_boot_cpu(void)
 {
 	unsigned int cpu = smp_processor_id();
 
+	per_cpu(cpu_data, cpu).idle = current;
+
 	cpu_set(cpu, cpu_possible_map);
 	cpu_set(cpu, cpu_present_map);
 	cpu_set(cpu, cpu_online_map);

include/asm-arm/cpu.h

@@ -16,6 +16,7 @@
 struct cpuinfo_arm {
 	struct cpu	cpu;
 #ifdef CONFIG_SMP
+	struct task_struct *idle;
 	unsigned int	loops_per_jiffy;
 #endif
 };