Also, I've just realized that the check is racy... Could you please move the whole check block (between and excluding AcpiUtAcquireMutex and AcpiUtReleaseMutex) down right below the following lines: Status = AcpiUtAcquireMutex (ACPI_MTX_CACHES); if (ACPI_FAILURE (Status)) { return (Status); } Thank you. -- Andriy Gapon