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SubjectRe: [PATCH] Add TPM hardware enablement driver
Greg KH wrote:
> On Tue, Mar 22, 2005 at 09:02:24PM -0500, Jeff Garzik wrote:
>
>>Kylene Hall wrote:
>>
>>>>what is the purpose of this pci_dev_get/put? attempting to prevent
>>>>hotplug or
>>>>something?
>>>
>>>
>>>Seems that since there is a refernce to the device in the chip structure
>>>and I am making the file private data pointer point to that chip structure
>>>this is another reference that must be accounted for. If you remove it
>>>with it open and attempt read or write bad things will happen. This isn't
>>>really hotpluggable either as the TPM is on the motherboard.
>>
>>My point was that there will always be a reference -anyway-, AFAICS.
>>There is a pci_dev reference assigned to the pci_driver when the PCI
>>driver is loaded, and all uses by the TPM generic code of this pointer
>>are -inside- the pci_driver's pci_dev object lifetime.
>
>
> Think of the following situation:
> - driver is bound to device.
> - userspace opens char dev node.
> - device is removed from the system (using fakephp I can do this
> to _any_ pci device, even if it is on the motherboard.)
> - userspace writes to char dev node
> - driver attempts to access pci device structure that is no
> longer present in memory.
>
> Because of this open needs to get a reference to the pci device to
> prevent oopses, or the driver needs to be aware of "device is now gone"
> in some other manner.

Thanks for explaining; agreed.

However, there appear to still be massive bugs in this area:

Consider the behavior of the chrdev if a PCI device has been unplugged.
It's still actively messing with the non-existent hardware, and never
checks for dead h/w AFAICS.

Jeff


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