Messages in this thread | | | Date | Thu, 24 Mar 2005 16:04:25 -0500 | From | Jeff Garzik <> | Subject | Re: [PATCH] Add TPM hardware enablement driver |
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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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