1 files changed, 78 insertions, 22 deletions

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index d7f8cc18ae05..54faff91b805 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -57,6 +57,25 @@
 #define DBG(fmt...)
 #endif
 
+
+/* Store all idle threads, this can be reused instead of creating
+* a new thread. Also avoids complicated thread destroy functionality
+* for idle threads.
+*/
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * Needed only for CONFIG_HOTPLUG_CPU because __cpuinitdata is
+ * removed after init for !CONFIG_HOTPLUG_CPU.
+ */
+static DEFINE_PER_CPU(struct task_struct *, idle_thread_array);
+#define get_idle_for_cpu(x)      (per_cpu(idle_thread_array, x))
+#define set_idle_for_cpu(x, p)   (per_cpu(idle_thread_array, x) = (p))
+#else
+static struct task_struct *idle_thread_array[NR_CPUS] __cpuinitdata ;
+#define get_idle_for_cpu(x)      (idle_thread_array[(x)])
+#define set_idle_for_cpu(x, p)   (idle_thread_array[(x)] = (p))
+#endif
+
 struct thread_info *secondary_ti;
 
 DEFINE_PER_CPU(cpumask_var_t, cpu_sibling_map);
@@ -238,23 +257,6 @@ static void __devinit smp_store_cpu_info(int id)
         per_cpu(cpu_pvr, id) = mfspr(SPRN_PVR);
 }
 
-static void __init smp_create_idle(unsigned int cpu)
-{
-        struct task_struct *p;
-
-        /* create a process for the processor */
-        p = fork_idle(cpu);
-        if (IS_ERR(p))
-                panic("failed fork for CPU %u: %li", cpu, PTR_ERR(p));
-#ifdef CONFIG_PPC64
-        paca[cpu].__current = p;
-        paca[cpu].kstack = (unsigned long) task_thread_info(p)
-                + THREAD_SIZE - STACK_FRAME_OVERHEAD;
-#endif
-        current_set[cpu] = task_thread_info(p);
-        task_thread_info(p)->cpu = cpu;
-}
-
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
         unsigned int cpu;
@@ -288,10 +290,6 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
                         max_cpus = NR_CPUS;
         else
                 max_cpus = 1;
-
-        for_each_possible_cpu(cpu)
-                if (cpu != boot_cpuid)
-                        smp_create_idle(cpu);
 }
 
 void __devinit smp_prepare_boot_cpu(void)
@@ -355,9 +353,62 @@ void generic_set_cpu_dead(unsigned int cpu)
 }
 #endif
 
+struct create_idle {
+        struct work_struct work;
+        struct task_struct *idle;
+        struct completion done;
+        int cpu;
+};
+
+static void __cpuinit do_fork_idle(struct work_struct *work)
+{
+        struct create_idle *c_idle =
+                container_of(work, struct create_idle, work);
+
+        c_idle->idle = fork_idle(c_idle->cpu);
+        complete(&c_idle->done);
+}
+
+static int __cpuinit create_idle(unsigned int cpu)
+{
+        struct thread_info *ti;
+        struct create_idle c_idle = {
+                .cpu    = cpu,
+                .done   = COMPLETION_INITIALIZER_ONSTACK(c_idle.done),
+        };
+        INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
+
+        c_idle.idle = get_idle_for_cpu(cpu);
+
+        /* We can't use kernel_thread since we must avoid to
+         * reschedule the child. We use a workqueue because
+         * we want to fork from a kernel thread, not whatever
+         * userspace process happens to be trying to online us.
+         */
+        if (!c_idle.idle) {
+                schedule_work(&c_idle.work);
+                wait_for_completion(&c_idle.done);
+        } else
+                init_idle(c_idle.idle, cpu);
+        if (IS_ERR(c_idle.idle)) {              
+                pr_err("Failed fork for CPU %u: %li", cpu, PTR_ERR(c_idle.idle));
+                return PTR_ERR(c_idle.idle);
+        }
+        ti = task_thread_info(c_idle.idle);
+
+#ifdef CONFIG_PPC64
+        paca[cpu].__current = c_idle.idle;
+        paca[cpu].kstack = (unsigned long)ti + THREAD_SIZE - STACK_FRAME_OVERHEAD;
+#endif
+        ti->cpu = cpu;
+        current_set[cpu] = ti;
+
+        return 0;
+}
+
 int __cpuinit __cpu_up(unsigned int cpu)
 {
-        int c;
+        int rc, c;
 
         secondary_ti = current_set[cpu];
 
@@ -365,6 +416,11 @@ int __cpuinit __cpu_up(unsigned int cpu)
             (smp_ops->cpu_bootable && !smp_ops->cpu_bootable(cpu)))
                 return -EINVAL;
 
+        /* Make sure we have an idle thread */
+        rc = create_idle(cpu);
+        if (rc)
+                return rc;
+
         /* Make sure callin-map entry is 0 (can be leftover a CPU
          * hotplug
          */