Date: Thu, 24 Mar 2005 13:33:02 -0800
From: Greg KH <greg@kroah.com>
To: Jeff Garzik <jgarzik@pobox.com>
Cc: Kylene Hall <kjhall@us.ibm.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Add TPM hardware enablement driver
Message-ID: <20050324213302.GA26729@kroah.com>
References: <1110415321526@kroah.com> <422FC42B.7@pobox.com> <Pine.LNX.4.61.0503161811020.5212@jo.austin.ibm.com> <4240CE30.2060105@pobox.com> <20050324063933.GC10355@kroah.com> <42432B59.70003@pobox.com>
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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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