ftrace: separate out the function enabled variable

Currently the function tracer uses the global tracer_enabled variable that
is used to keep track if the tracer is enabled or not. The function tracing
startup needs to be separated out, otherwise the internal happenings of
the tracer startup is also recorded.

This patch creates a ftrace_function_enabled variable to all the starting
of the function traces to happen after everything has been started.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.c

@@ -96,6 +96,9 @@ static DEFINE_PER_CPU(struct trace_array_cpu, max_data);
 /* tracer_enabled is used to toggle activation of a tracer */
 static int			tracer_enabled = 1;
 
+/* function tracing enabled */
+int				ftrace_function_enabled;
+
 /*
  * trace_nr_entries is the number of entries that is allocated
  * for a buffer. Note, the number of entries is always rounded
@@ -134,6 +137,7 @@ static notrace void no_trace_init(struct trace_array *tr)
 {
 	int cpu;
 
+	ftrace_function_enabled = 0;
 	if(tr->ctrl)
 		for_each_online_cpu(cpu)
 			tracing_reset(tr->data[cpu]);
@@ -985,7 +989,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip)
 	long disabled;
 	int cpu;
 
-	if (unlikely(!tracer_enabled))
+	if (unlikely(!ftrace_function_enabled))
 		return;
 
 	if (skip_trace(ip))
@@ -1010,11 +1014,15 @@ static struct ftrace_ops trace_ops __read_mostly =
 
 void tracing_start_function_trace(void)
 {
+	ftrace_function_enabled = 0;
 	register_ftrace_function(&trace_ops);
+	if (tracer_enabled)
+		ftrace_function_enabled = 1;
 }
 
 void tracing_stop_function_trace(void)
 {
+	ftrace_function_enabled = 0;
 	unregister_ftrace_function(&trace_ops);
 }
 #endif
@@ -1850,8 +1858,10 @@ __tracing_open(struct inode *inode, struct file *file, int *ret)
 		m->private = iter;
 
 		/* stop the trace while dumping */
-		if (iter->tr->ctrl)
+		if (iter->tr->ctrl) {
 			tracer_enabled = 0;
+			ftrace_function_enabled = 0;
+		}
 
 		if (iter->trace && iter->trace->open)
 			iter->trace->open(iter);
@@ -1884,8 +1894,14 @@ int tracing_release(struct inode *inode, struct file *file)
 		iter->trace->close(iter);
 
 	/* reenable tracing if it was previously enabled */
-	if (iter->tr->ctrl)
+	if (iter->tr->ctrl) {
 		tracer_enabled = 1;
+		/*
+		 * It is safe to enable function tracing even if it
+		 * isn't used
+		 */
+		ftrace_function_enabled = 1;
+	}
 	mutex_unlock(&trace_types_lock);
 
 	seq_release(inode, file);