On Wed, 2017-02-08 at 15:13 -0500, Steven Rostedt wrote:

On Wed,  8 Feb 2017 11:24:58 -0600
Tom Zanussi [off-list ref] wrote:

quoted

 static void destroy_hist_field(struct hist_field *hist_field)
 {
+	unsigned int i;
+
+	if (!hist_field)
+		return;
+
+	for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++)
+		destroy_hist_field(hist_field->operands[i]);

Recursive functions get me really nervous. What limits it? Is this user
defined? Perhaps we need to find a better way to handle this that's not
recursive, or at least put in a hard limit of the amount it can recurse.

It's limited by the expression depth, which shouldn't be more than 1
deep, but you're right, there should be an explicit limit check, just in
case - will add one.

Tom

-- Steve

quoted

+
 	kfree(hist_field);
 }
 

@@ -377,7 +393,10 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 	}
 
 	if (flags & HIST_FIELD_FL_LOG2) {
+		unsigned long fl = flags & ~HIST_FIELD_FL_LOG2;
 		hist_field->fn = hist_field_log2;
+		hist_field->operands[0] = create_hist_field(field, fl);
+		hist_field->size = hist_field->operands[0]->size;
 		goto out;
 	}