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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