Nonpaged memory pointer

Question

I have 2 structures declared:

struct irp_list {
   IRP *irp;
   LIST_ENTRY lh;
};

and

struct dev_info {
...
   LIST_ENTRY lh;
...
};

Inside DriverWrite function (IRP_MJ_WRITE) I do:

struct irp_list *il;
struct dev_info *di = (struct dev_info*)device->DeviceExtension;

if (!(il = ExAllocatePool(NonPagedPool, sizeof(*il)))) {
    ret = STATUS_NO_MEMORY;
    DbgPrint("[uart] UartWrite can't handle irp...\n");
    goto error;
}

il->irp = irp;  // store DriverWrite irp

InsertTailList(&di->lh, &il->lh);   // this insert is not failing...
irp->IoStatus.Information = 0;
IoMarkIrpPending(irp);

return STATUS_PENDING;

Inside a DPC function I try access the nonpaged memory of il with:

struct dev_info* di;
di = (struct dev_info*)device->DeviceExtension;

if(!IsListEmpty(&di->lh))
{
// code never reached
}

I know that a DPC can only read nonpaged memory, but why is !IsListEmpty always returning FALSE as if the insert failed?

Answer 1

This may not be a proper answer, but it's a bit too complicated for a comment, so I'm writing it as an answer, for proper formatting, etc:

Reading the docs for InsertTailList:

VOID InsertTailList(
  _Inout_  PLIST_ENTRY ListHead,
  _Inout_  PLIST_ENTRY Entry
);

InsertTailList updates ListHead->Blink to point to Entry. It updates Entry->Blink to point to the old last entry in the list, and sets Entry->Flink to ListHead. The Flink of the previous last entry is updated to point to Entry as well.

Where IsListEmpty says:

IsListEmpty returns TRUE if there are currently no entries in the list and FALSE otherwise.

Remarks

IsListEmpty returns TRUE if ListHead->Flink refers back to ListHead.

Now, I'm not sure if I understand all of this, but to me, it seems like ListHead->Flink is not updated by InsertListTail (which seems rather strange). Although the sentence

The Flink of the previous last entry is updated to point to Entry as well.

may indicate that it does indeed update the head if it's the only thing in the list.

(Gah, just spotted the comment saying you've solved it).