function_graph: Have profiler use new helper ftrace_graph_get_ret_stack()

The ret_stack processing is going to change, and that is going
to break anything that is accessing the ret_stack directly. One user is the
function graph profiler. By using the ftrace_graph_get_ret_stack() helper
function, the profiler can access the ret_stack entry without relying on the
implementation details of the stack itself.
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/ftrace.h

@@ -785,6 +785,9 @@ extern int
 function_graph_enter(unsigned long ret, unsigned long func,
 		     unsigned long frame_pointer, unsigned long *retp);
 
+struct ftrace_ret_stack *
+ftrace_graph_get_ret_stack(struct task_struct *task, int idx);
+
 unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
 				    unsigned long ret, unsigned long *retp);
 

kernel/trace/fgraph.c

@@ -232,6 +232,17 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
 	return ret;
 }
 
+struct ftrace_ret_stack *
+ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
+{
+	idx = current->curr_ret_stack - idx;
+
+	if (idx >= 0 && idx <= task->curr_ret_stack)
+		return &current->ret_stack[idx];
+
+	return NULL;
+}
+
 /**
  * ftrace_graph_ret_addr - convert a potentially modified stack return address
  *			   to its original value

kernel/trace/ftrace.c

@@ -792,7 +792,7 @@ void ftrace_graph_graph_time_control(bool enable)
 
 static int profile_graph_entry(struct ftrace_graph_ent *trace)
 {
-	int index = current->curr_ret_stack;
+	struct ftrace_ret_stack *ret_stack;
 
 	function_profile_call(trace->func, 0, NULL, NULL);
 
@@ -800,14 +800,16 @@ static int profile_graph_entry(struct ftrace_graph_ent *trace)
 	if (!current->ret_stack)
 		return 0;
 
-	if (index >= 0 && index < FTRACE_RETFUNC_DEPTH)
-		current->ret_stack[index].subtime = 0;
+	ret_stack = ftrace_graph_get_ret_stack(current, 0);
+	if (ret_stack)
+		ret_stack->subtime = 0;
 
 	return 1;
 }
 
 static void profile_graph_return(struct ftrace_graph_ret *trace)
 {
+	struct ftrace_ret_stack *ret_stack;
 	struct ftrace_profile_stat *stat;
 	unsigned long long calltime;
 	struct ftrace_profile *rec;
@@ -825,16 +827,15 @@ static void profile_graph_return(struct ftrace_graph_ret *trace)
 	calltime = trace->rettime - trace->calltime;
 
 	if (!fgraph_graph_time) {
-		int index;
-
-		index = current->curr_ret_stack;
 
 		/* Append this call time to the parent time to subtract */
-		if (index)
-			current->ret_stack[index - 1].subtime += calltime;
+		ret_stack = ftrace_graph_get_ret_stack(current, 1);
+		if (ret_stack)
+			ret_stack->subtime += calltime;
 
-		if (current->ret_stack[index].subtime < calltime)
-			calltime -= current->ret_stack[index].subtime;
+		ret_stack = ftrace_graph_get_ret_stack(current, 0);
+		if (ret_stack && ret_stack->subtime < calltime)
+			calltime -= ret_stack->subtime;
 		else
 			calltime = 0;
 	}