struct vbg_dev *vbg_get_gdev(void)
{
	mutex_lock(&vbg_gdev_mutex);

	/*
	 * Note on success we keep the mutex locked until vbg_put_gdev(),
	 * this stops vbg_pci_remove from removing the device from underneath
	 * vboxsf. vboxsf will only hold a reference for a short while.
	 */
	if (vbg_gdev)
		return vbg_gdev;

	mutex_unlock(&vbg_gdev_mutex);
	return ERR_PTR(-ENODEV);
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.