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SubjectRe: refcount leak in pci_get_device()?
On Thu, Aug 21, 2008 at 02:19:18PM -0600, Alex Chiang wrote:
> Hi Greg,
>
> While playing around with my slot symlink stuff, I noticed that
> the following sequence is problematic:
>
> 1. clean boot
> 2. modprobe acpiphp
> 3. echo 0 > /sys/bus/pci/slots/N/power
> 4. ???
>
> After step 3, we *should* be seeing pci_release_dev() getting
> called, but we never do because the refcount on the device is
> still quite high (5 or 6, on my ia64 system).
>
> I'm still trying to track this down, but I did notice, via code
> inspection, at least one suspicious area:
>
> #define for_each_pci_dev(d) while ((d = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, d)) != NULL)
>
> That eventually calls pci_get_dev_by_id(), which increases the
> refcount on the device, but never decrements it.
>
> Looks like that change in behavior happened here:
>
> PCI: clean up search.c a lot
> 95247b57ed844511a212265b45cf9a919753aea1
>
> pci_get_device() used to decrement the refcount, but no longer
> does.

No, pci_get_device() never decremented the refcount, and that didn't
change in the above git commit.

The description of pci_get_device() says that a reference is grabbed:
Iterates through the list of known PCI devices. If a PCI device
is found with a matching @vendor and @device, the reference
count to the device is incremented and a pointer to its device
structure is returned. Otherwise, %NULL is returned. A new
search is initiated by passing %NULL as the @from argument.
Otherwise if @from is not %NULL, searches continue from next
device on the global list. The reference count for @from is
always decremented if it is not %NULL.


All of the pci_find* functions should not have grabbed a reference to
the device, as that was the "old" behavior. All of the pci_get*
functions do grab a reference.

Did I somehow mess up and one of the pci_find* functions now improperly
increment a reference? Hopefully we shouldn't be using those functions
anymore as they aren't hotplug safe...

thanks,

greg k-h


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