On Thu, Mar 24, 2005 at 04:04:25PM -0500, Jeff Garzik wrote:
> 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.
I agree, the driver should be fixed to handle this properly.
thanks,
greg k-h
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