tracing: Use one prologue for the preempt irqs off tracer function tracers

The preempt and irqsoff tracers have three types of function tracers.
Normal function tracer, function graph entry, and function graph return.
Each of these use a complex dance to prevent recursion and whether
to trace the data or not (depending if interrupts are enabled or not).

This patch moves the duplicate code into a single routine, to
prevent future mistakes with modifying duplicate complex code.

Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_irqsoff.c

@@ -87,14 +87,22 @@ static __cacheline_aligned_in_smp	unsigned long max_sequence;
 
 #ifdef CONFIG_FUNCTION_TRACER
 /*
- * irqsoff uses its own tracer function to keep the overhead down:
+ * Prologue for the preempt and irqs off function tracers.
+ *
+ * Returns 1 if it is OK to continue, and data->disabled is
+ *            incremented.
+ *         0 if the trace is to be ignored, and data->disabled
+ *            is kept the same.
+ *
+ * Note, this function is also used outside this ifdef but
+ *  inside the #ifdef of the function graph tracer below.
+ *  This is OK, since the function graph tracer is
+ *  dependent on the function tracer.
  */
-static void
-irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip)
+static int func_prolog_dec(struct trace_array *tr,
+			   struct trace_array_cpu **data,
+			   unsigned long *flags)
 {
-	struct trace_array *tr = irqsoff_trace;
-	struct trace_array_cpu *data;
-	unsigned long flags;
 	long disabled;
 	int cpu;
 
@@ -106,18 +114,38 @@ irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip)
 	 */
 	cpu = raw_smp_processor_id();
 	if (likely(!per_cpu(tracing_cpu, cpu)))
-		return;
+		return 0;
 
-	local_save_flags(flags);
+	local_save_flags(*flags);
 	/* slight chance to get a false positive on tracing_cpu */
-	if (!irqs_disabled_flags(flags))
-		return;
+	if (!irqs_disabled_flags(*flags))
+		return 0;
 
-	data = tr->data[cpu];
-	disabled = atomic_inc_return(&data->disabled);
+	*data = tr->data[cpu];
+	disabled = atomic_inc_return(&(*data)->disabled);
 
 	if (likely(disabled == 1))
-		trace_function(tr, ip, parent_ip, flags, preempt_count());
+		return 1;
+
+	atomic_dec(&(*data)->disabled);
+
+	return 0;
+}
+
+/*
+ * irqsoff uses its own tracer function to keep the overhead down:
+ */
+static void
+irqsoff_tracer_call(unsigned long ip, unsigned long parent_ip)
+{
+	struct trace_array *tr = irqsoff_trace;
+	struct trace_array_cpu *data;
+	unsigned long flags;
+
+	if (!func_prolog_dec(tr, &data, &flags))
+		return;
+
+	trace_function(tr, ip, parent_ip, flags, preempt_count());
 
 	atomic_dec(&data->disabled);
 }
@@ -155,30 +183,16 @@ static int irqsoff_graph_entry(struct ftrace_graph_ent *trace)
 	struct trace_array *tr = irqsoff_trace;
 	struct trace_array_cpu *data;
 	unsigned long flags;
-	long disabled;
 	int ret;
-	int cpu;
 	int pc;
 
-	cpu = raw_smp_processor_id();
-	if (likely(!per_cpu(tracing_cpu, cpu)))
+	if (!func_prolog_dec(tr, &data, &flags))
 		return 0;
 
-	local_save_flags(flags);
-	/* slight chance to get a false positive on tracing_cpu */
-	if (!irqs_disabled_flags(flags))
-		return 0;
-
-	data = tr->data[cpu];
-	disabled = atomic_inc_return(&data->disabled);
-
-	if (likely(disabled == 1)) {
-		pc = preempt_count();
-		ret = __trace_graph_entry(tr, trace, flags, pc);
-	} else
-		ret = 0;
-
+	pc = preempt_count();
+	ret = __trace_graph_entry(tr, trace, flags, pc);
 	atomic_dec(&data->disabled);
+
 	return ret;
 }
 
@@ -187,27 +201,13 @@ static void irqsoff_graph_return(struct ftrace_graph_ret *trace)
 	struct trace_array *tr = irqsoff_trace;
 	struct trace_array_cpu *data;
 	unsigned long flags;
-	long disabled;
-	int cpu;
 	int pc;
 
-	cpu = raw_smp_processor_id();
-	if (likely(!per_cpu(tracing_cpu, cpu)))
+	if (!func_prolog_dec(tr, &data, &flags))
 		return;
 
-	local_save_flags(flags);
-	/* slight chance to get a false positive on tracing_cpu */
-	if (!irqs_disabled_flags(flags))
-		return;
-
-	data = tr->data[cpu];
-	disabled = atomic_inc_return(&data->disabled);
-
-	if (likely(disabled == 1)) {
-		pc = preempt_count();
-		__trace_graph_return(tr, trace, flags, pc);
-	}
-
+	pc = preempt_count();
+	__trace_graph_return(tr, trace, flags, pc);
 	atomic_dec(&data->disabled);
 }