Merge branches 'tracing/ftrace' and 'tracing/urgent' into tracing/core

kernel/trace/ftrace.c

···
 static int start_graph_tracing(void)
 {
 	struct ftrace_ret_stack **ret_stack_list;
-	int ret;
+	int ret, cpu;
 
 	ret_stack_list = kmalloc(FTRACE_RETSTACK_ALLOC_SIZE *
 				sizeof(struct ftrace_ret_stack *),
···
 
 	if (!ret_stack_list)
 		return -ENOMEM;
+
+	/* The cpu_boot init_task->ret_stack will never be freed */
+	for_each_online_cpu(cpu)
+		ftrace_graph_init_task(idle_task(cpu));
 
 	do {
 		ret = alloc_retstack_tasklist(ret_stack_list);