3 files changed, 48 insertions, 8 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index dcd6a7c3a435..ca29e03c1fac 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -428,6 +428,7 @@ extern void unregister_ftrace_graph(void);
 
 extern void ftrace_graph_init_task(struct task_struct *t);
 extern void ftrace_graph_exit_task(struct task_struct *t);
+extern void ftrace_graph_init_idle_task(struct task_struct *t, int cpu);
 
 static inline int task_curr_ret_stack(struct task_struct *t)
 {
@@ -451,6 +452,7 @@ static inline void unpause_graph_tracing(void)
 
 static inline void ftrace_graph_init_task(struct task_struct *t) { }
 static inline void ftrace_graph_exit_task(struct task_struct *t) { }
+static inline void ftrace_graph_init_idle_task(struct task_struct *t, int cpu) { }
 
 static inline int register_ftrace_graph(trace_func_graph_ret_t retfunc,
                           trace_func_graph_ent_t entryfunc)
diff --git a/kernel/sched.c b/kernel/sched.c
index 18d38e4ec7ba..fbe86cb04b61 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5571,7 +5571,7 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
          * The idle tasks have their own, simple scheduling class:
          */
         idle->sched_class = &idle_sched_class;
-        ftrace_graph_init_task(idle);
+        ftrace_graph_init_idle_task(idle, cpu);
 }
 
 /*
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f3dadae83883..888b611897d3 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3328,7 +3328,7 @@ static int start_graph_tracing(void)
         /* The cpu_boot init_task->ret_stack will never be freed */
         for_each_online_cpu(cpu) {
                 if (!idle_task(cpu)->ret_stack)
-                        ftrace_graph_init_task(idle_task(cpu));
+                        ftrace_graph_init_idle_task(idle_task(cpu), cpu);
         }
 
         do {
@@ -3418,6 +3418,49 @@ void unregister_ftrace_graph(void)
         mutex_unlock(&ftrace_lock);
 }
 
+static DEFINE_PER_CPU(struct ftrace_ret_stack *, idle_ret_stack);
+
+static void
+graph_init_task(struct task_struct *t, struct ftrace_ret_stack *ret_stack)
+{
+        atomic_set(&t->tracing_graph_pause, 0);
+        atomic_set(&t->trace_overrun, 0);
+        t->ftrace_timestamp = 0;
+        /* make curr_ret_stack visable before we add the ret_stack */
+        smp_wmb();
+        t->ret_stack = ret_stack;
+}
+
+/*
+ * Allocate a return stack for the idle task. May be the first
+ * time through, or it may be done by CPU hotplug online.
+ */
+void ftrace_graph_init_idle_task(struct task_struct *t, int cpu)
+{
+        t->curr_ret_stack = -1;
+        /*
+         * The idle task has no parent, it either has its own
+         * stack or no stack at all.
+         */
+        if (t->ret_stack)
+                WARN_ON(t->ret_stack != per_cpu(idle_ret_stack, cpu));
+
+        if (ftrace_graph_active) {
+                struct ftrace_ret_stack *ret_stack;
+
+                ret_stack = per_cpu(idle_ret_stack, cpu);
+                if (!ret_stack) {
+                        ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
+                                            * sizeof(struct ftrace_ret_stack),
+                                            GFP_KERNEL);
+                        if (!ret_stack)
+                                return;
+                        per_cpu(idle_ret_stack, cpu) = ret_stack;
+                }
+                graph_init_task(t, ret_stack);
+        }
+}
+
 /* Allocate a return stack for newly created task */
 void ftrace_graph_init_task(struct task_struct *t)
 {
@@ -3433,12 +3476,7 @@ void ftrace_graph_init_task(struct task_struct *t)
                                 GFP_KERNEL);
                 if (!ret_stack)
                         return;
-                atomic_set(&t->tracing_graph_pause, 0);
-                atomic_set(&t->trace_overrun, 0);
-                t->ftrace_timestamp = 0;
-                /* make curr_ret_stack visable before we add the ret_stack */
-                smp_wmb();
-                t->ret_stack = ret_stack;
+                graph_init_task(t, ret_stack);
         }
 }