tracing/kprobes: Avoid self tests if tracing is disabled on boot up

If tracing is disabled on boot up, the kernel should not execute tracing
self tests. The kernel should check whether tracing is disabled or not
before executing any of the tracing self tests.

Link: http://lkml.kernel.org/p/20140605223520.32311.56097.stgit@yunodevel

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_kprobe.c

@@ -1377,6 +1377,9 @@ static __init int kprobe_trace_self_tests_init(void)
 	struct trace_kprobe *tk;
 	struct ftrace_event_file *file;
 
+	if (tracing_is_disabled())
+		return -ENODEV;
+
 	target = kprobe_trace_selftest_target;
 
 	pr_info("Testing kprobe tracing: ");