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    <p>At the time <code>DriverUnload</code> is called there're no more created devices. Hence - it's obsolete to try to use <code>DeviceObject</code> and <code>NextDevice</code> members of the <code>DRIVER_OBJECT</code> structure.</p> <p>What's surprising is that <code>NextDevice</code> isn't set to <code>NULL</code>, according to your debug output, but nevertheless it's just a technical note.</p> <p>If you want to do a per-device cleanup you should rather do it in your dispatch routine in response to <code>IRP_MJ_CLOSE</code>.</p> <p><strong>UPD</strong></p> <p>The question author posted in the comments that iterating through the created devices in the driver unload routine is a common practice, and provided the reference article at the codeproject, with the appropriate source code.</p> <p>After reading the article and the source code it became more clear.</p> <p>Usually the driver "creates a device" (i.e. calls <code>IoCreateDevice</code>) in response to the OS request, which originates from a call to <code>CreateFile</code> (or similar). When the device handle is closed - driver receives the appropriate request and "destroys" the device (<code>IoDeleteDevice</code>). The OS will not unload the driver if there're open handles to its devices, hence within the driver uninitialization routine there are no created devices.</p> <p>However the driver in the reference article doesn't follow this logic. It creates the device at the beginning, right in its initialization routine <code>DriverEntry</code>. This does not prevent the OS from unloading the driver, because there're no open references to this device, hence the driver really needs to do the device cleanup in its <code>DriverUnload</code>.</p> <p>Alright, this makes sense now. Except, from my personal experience, it's <strong>not</strong> a common practice to work this way, but this is not forbidden nevertheless.</p> <p>Now, regarding your problem. Maybe you just made a mistake in the loop? I mean:</p> <pre><code>while (pNextObj != NULL) { PDEVICE_EXTENSION pDevExt = (PDEVICE_EXTENSION) pNextObj-&gt;DeviceExtension; // ... pNextObj = pNextObj-&gt;NextDevice; // then delete the device using the Extension IoDeleteDevice( pDevExt-&gt;pDevice ); } </code></pre> <p>Are you sure you do the things in the same order? Means, you first get the pointer to the next device object, and then call <code>IoDeleteDevice</code>?</p> <p>Please post the whole code of your <code>DriverUnload</code> if you still have the problem.</p>
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    1. POmemory read error in my DriverUnload callback,which causes BSOD,why?
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    1. CO@valdo,for NT driver,the device still exists in `DriverUnload`.
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    2. CO@compile-fan: what makes you think so? AFAIK `DriverUnload` is the driver's global cleanup routine. This is the function to be called last before the driver is finally unloaded. If you were right - this would mean that the driver gets unloaded without being notified about device deleteion - hence without destroying the companion device extension data. This means memory leaks. Also, how would the OS manage the device without the corresponding driver?
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    3. CO@compile-fan: Also, the system may load the driver, call its `DriverEntry`, then call its `DriverUnload` and then unload it. Without creating the device at all! How would the device "still exist"? I think you confuse between the "device" data and "driver extension" data. The driver extension data definitely should be valid at `DriverUnload`. Because it's a global data, allocated at `DriverEntry`, as opposed to per-device extension data, allocated in `AddDevice` routine.
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