Index: linux-3.1/drivers/cbus/tahvo.c
===================================================================
--- linux-3.1.orig/drivers/cbus/tahvo.c	2011-11-05 17:03:39.598846119 +0100
+++ linux-3.1/drivers/cbus/tahvo.c	2011-11-05 17:04:36.274768324 +0100
@@ -104,7 +104,9 @@ void tahvo_write_reg(struct device *chil
 {
 	struct tahvo		*tahvo = dev_get_drvdata(child->parent);
 
+	mutex_lock(&tahvo->mutex);
 	__tahvo_write_reg(tahvo, reg, val);
+	mutex_unlock(&tahvo->mutex);
 }
 EXPORT_SYMBOL(tahvo_write_reg);