蓝屏求助：有关MDL

我要用TDI实现数据的发送和接收，发送代码如下：

NTSTATUS
TdiSend(
IN PFILE_OBJECT pEndPointObject,
IN PVOID pBuffer,
IN ULONG Length
)
{
PDEVICE_OBJECT pDeviceObject;
KEVENT Event;
IO_STATUS_BLOCK IoStatus;
PIRP pIrp;
PMDL pMdl;
NTSTATUS status;

dprintf(\"Sending...\\n\");

pDeviceObject = IoGetRelatedDeviceObject(pEndPointObject);

KeInitializeEvent(&Event, NotificationEvent, FALSE);

pIrp = TdiBuildInternalDeviceControlIrp(
TDI_SEND,
pDeviceObject,
pEndPointObject,
&Event,
&IoStatus
);

if( NULL == pIrp )
{
dprintf(\"TdiSend():Insufficient Resources\\n\");
return STATUS_INSUFFICIENT_RESOURCES;
}

pMdl = IoAllocateMdl(
pBuffer,
Length,
FALSE,
FALSE,
pIrp
);

if( NULL == pMdl )
{
dprintf(\"TdiSend():Fail to allocate the mdl\");
return STATUS_INSUFFICIENT_RESOURCES;
}

   _try
   {
      MmProbeAndLockPages( pMdl, KernelMode, IoModifyAccess );
   }
   _except( EXCEPTION_EXECUTE_HANDLER )
   {
      IoFreeMdl( pMdl );
      pMdl = NULL;
      return STATUS_INSUFFICIENT_RESOURCES;
   }

TdiBuildSend(
pIrp,
pDeviceObject,
pEndPointObject,
NULL,
NULL,
pMdl,
0,
Length
);

status = IoCallDriver(pDeviceObject, pIrp);
if( STATUS_PENDING == status )
{
dprintf(\"Waiting to send\");
status = KeWaitForSingleObject(&Event, UserRequest, KernelMode, FALSE, 0);
}

if( !NT_SUCCESS(status) )
{
dprintf(\"Fail to Send\\n\");
return status;
}

if( !NT_SUCCESS(IoStatus.Status) )
{

dprintf(\"Fail to Send\\n\");
return IoStatus.Status;
}

dprintf(\"Success to Send %u bytes\\n\", IoStatus.Information);

MmUnlockPages(pMdl);
IoFreeMdl(pMdl);

return IoStatus.Status;
}

问题是我这代码执行时，运行一次没有问题，如果调用两次就有出现蓝屏了,我测试出来好象是
IoFreeMdl(pMdl);
的问题，因为当我把这行代码注释掉就没有问题了，可是肯定需要释放的呀，这是怎么回事呢？

这与驱动的I/O方式有关吗？我是新手，许多东西都不懂，我在这个问题上已经困惑几天了

没有人回答吗？