diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index a335006923ec..40ae7379cbf5 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1759,7 +1759,7 @@ static void expr_field_str(struct hist_field *field, char *expr)
 
 static char *expr_str(struct hist_field *field, unsigned int level)
 {
-	char *expr;
+	char *expr __free(kfree) = NULL;
 
 	if (level > 1)
 		return NULL;
@@ -1770,7 +1770,7 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 
 	if (!field->operands[0]) {
 		expr_field_str(field, expr);
-		return expr;
+		return_ptr(expr);
 	}
 
 	if (field->operator == FIELD_OP_UNARY_MINUS) {
@@ -1778,16 +1778,15 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 
 		strcat(expr, "-(");
 		subexpr = expr_str(field->operands[0], ++level);
-		if (!subexpr) {
-			kfree(expr);
+		if (!subexpr)
 			return NULL;
-		}
+
 		strcat(expr, subexpr);
 		strcat(expr, ")");
 
 		kfree(subexpr);
 
-		return expr;
+		return_ptr(expr);
 	}
 
 	expr_field_str(field->operands[0], expr);
@@ -1806,13 +1805,12 @@ static char *expr_str(struct hist_field *field, unsigned int level)
 		strcat(expr, "*");
 		break;
 	default:
-		kfree(expr);
 		return NULL;
 	}
 
 	expr_field_str(field->operands[1], expr);
 
-	return expr;
+	return_ptr(expr);
 }
 
 /*