Unloading WDM mouse filter driver requires additional mouse click

Question

I looked up the mouse filter driver projects on github, there is a global variable call pendingKey in every one of them.

• The variable is increased in DispatchRead function
• and is decreased in ReadComplete function

The devices created can be safely detached and deleted if pendingKey equals 0 when Unload function is called.

NTSTATUS DispatchRead(PDEVICE_OBJECT DeviceObject, PIRP Irp)
{
    PDEVICE_EXTENSION devExt;
    PIO_STACK_LOCATION currentIrpStack;
    PIO_STACK_LOCATION nextIrpStack;

    currentIrpStack = IoGetCurrentIrpStackLocation(Irp);
    nextIrpStack = IoGetNextIrpStackLocation(Irp);

    *nextIrpStack = *currentIrpStack;

    pendingKey++;
    IoSetCompletionRoutine(Irp, ReadComplete, NULL, TRUE, TRUE, TRUE);

    return IoCallDriver(((PDEVICE_EXTENSION)DeviceObject->DeviceExtension)->LowerDevice, Irp);
}

NTSTATUS ReadComplete(PDEVICE_OBJECT DeviceObject, PIRP Irp, PVOID Context)
{
    PMOUSE_INPUT_DATA input = (PMOUSE_INPUT_DATA)Irp->AssociatedIrp.SystemBuffer;
    int structnum = Irp->IoStatus.Information / sizeof(MOUSE_INPUT_DATA);

    if (Irp->PendingReturned)
    {
        IoMarkIrpPending(Irp);
    }
    pendingKey--;
    return Irp->IoStatus.Status;

}

VOID Unload(IN PDRIVER_OBJECT DriverObject)
{
    LARGE_INTEGER interval = { 0 };
    PDEVICE_OBJECT DeviceObject = DriverObject->DeviceObject;
    interval.QuadPart = -10 * 1000 * 1000;

    int count = 0;
    while (DeviceObject) 
    {
        IoDetachDevice(((PDEVICE_EXTENSION)DeviceObject->DeviceExtension)->LowerDevice);
        DeviceObject = DeviceObject->NextDevice;
    }
    while (pendingKey) 
    {
        KeDelayExecutionThread(KernelMode, FALSE, &interval);
    }

    DeviceObject = DriverObject->DeviceObject;
    while (DeviceObject) 
    {
        IoDeleteDevice(DeviceObject);
        DeviceObject = DeviceObject->NextDevice;
    }

    DbgPrintEx(DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL, "Unloaded\r\n");
}

The Extra Mouse Click Problem

The problem is, after Unload function is called, I have to click the mouse once more or it stucks in the waiting loop，which means pendingkey is bigger than 0.

    while (pendingKey) 
    {
        KeDelayExecutionThread(KernelMode, FALSE, &interval);
    }

So someone please tell me how can I unload the driver without having to click the mouse.