tracing: Use hist trigger's var_ref array to destroy var_refs

Since every var ref for a trigger has an entry in the var_ref[] array,
use that to destroy the var_refs, instead of piecemeal via the field
expressions.

This allows us to avoid having to keep and treat differently separate
lists for the action-related references, which future patches will
remove.

Link: http://lkml.kernel.org/r/fad1a164f0e257c158e70d6eadbf6c586e04b2a2.1545161087.git.tom.zanussi@linux.intel.com

Acked-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -2190,6 +2190,15 @@ static int contains_operator(char *str)
 	return field_op;
 }
 
+static void __destroy_hist_field(struct hist_field *hist_field)
+{
+	kfree(hist_field->var.name);
+	kfree(hist_field->name);
+	kfree(hist_field->type);
+
+	kfree(hist_field);
+}
+
 static void destroy_hist_field(struct hist_field *hist_field,
 			       unsigned int level)
 {
@@ -2201,14 +2210,13 @@ static void destroy_hist_field(struct hist_field *hist_field,
 	if (!hist_field)
 		return;
 
+	if (hist_field->flags & HIST_FIELD_FL_VAR_REF)
+		return; /* var refs will be destroyed separately */
+
 	for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++)
 		destroy_hist_field(hist_field->operands[i], level + 1);
 
-	kfree(hist_field->var.name);
-	kfree(hist_field->name);
-	kfree(hist_field->type);
-
-	kfree(hist_field);
+	__destroy_hist_field(hist_field);
 }
 
 static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
@@ -2335,6 +2343,12 @@ static void destroy_hist_fields(struct hist_trigger_data *hist_data)
 			hist_data->fields[i] = NULL;
 		}
 	}
+
+	for (i = 0; i < hist_data->n_var_refs; i++) {
+		WARN_ON(!(hist_data->var_refs[i]->flags & HIST_FIELD_FL_VAR_REF));
+		__destroy_hist_field(hist_data->var_refs[i]);
+		hist_data->var_refs[i] = NULL;
+	}
 }
 
 static int init_var_ref(struct hist_field *ref_field,