A call to a critical operating system function is stalled. The pregion and pregion type associated with the location of a call module originating the call is determined. In one embodiment, when the pregion type is either a stack or a heap pregion type, protective action is taken, such as terminating the call, otherwise the call is released. In another embodiment, when the pregion type is either a text or shared memory pregion type, the call is released, otherwise protective action is taken.