Re: [PATCH 02/13] PCI: prevent duplicate slot names

Kenji Kaneshige
2008-09-11T02:45:08Z

Hi Alex-san,

Thank you very much for your continuous effort.
I have one comment about the new design. Please see below.

>> I found another problem in pci_hp_register() that would be more complex
>> to fix than above-mentioned problem. Here is a pci_hp_register() with
>> all of your patch applied.
>>
>> int pci_hp_register(struct hotplug_slot *slot, struct pci_bus *bus, int slot_nr,
>> const char *name)
>> {
>> (snip...)
>>
>> /*
>> * No problems if we call this interface from both ACPI_PCI_SLOT
>> * driver and call it here again. If we've already created the
>> * pci_slot, the interface will simply bump the refcount.
>> */
>> pci_slot = pci_create_slot(bus, slot_nr, name);
>> if (IS_ERR(pci_slot))
>> return PTR_ERR(pci_slot);
>>
>> if (pci_slot->hotplug) {
>> dbg("%s: already claimed\n", __func__);
>> pci_destroy_slot(pci_slot);
>> return -EBUSY;
>> }
>>
>> slot->pci_slot = pci_slot;
>> pci_slot->hotplug = slot;
>>
>> /*
>> * Allow pcihp drivers to override the ACPI_PCI_SLOT name.
>> */
>> if (strcmp(kobject_name(&pci_slot->kobj), name)) {
>> result = kobject_rename(&pci_slot->kobj, name);
>> if (result) {
>> pci_destroy_slot(pci_slot);
>> return result;
>> }
>> }
>>
>> (snip...)
>> }
>>
>> If name duplication was detected in pci_create_slot(), it renames the
>> slot name like 'N-1' and return successfully. Even though slot's kobject
>> name was registered as 'N-1', 'name' array still have 'N' at this point.
>> So the following 'if' statement becomes true unexpectedly.
>>
>> /*
>> * Allow pcihp drivers to override the ACPI_PCI_SLOT name.
>> */
>> if (strcmp(kobject_name(&pci_slot->kobj), name)) {
>>
>> Then pci_hp_register() attempt to rename the slot name with 'N' again
>> by calling kobject_rename(), but it fails because there already exists
>> kobject with name 'N'. As a result, pci_hp_register() will fail.
>
> Yes, you are right, that is a problem.
>
> I've taken the following approach:
>
> - the above code is providing a mechanism to allow a
> _hotplug_ driver to override a _detection_ driver slot
> name.
>
> - in other words, we only have to worry about the case
> when a _detection_ driver was loaded before a _hotplug_
> driver.
>
> - we can ignore the case where another _hotplug_ driver
> was loaded first, because we'll already return -EBUSY.
>
> - so, to figure out if a _detection_ driver has already
> been loaded, we check to see if the pci_dev already has
> a valid pci_slot pointer.

We need to take into account that the hotplug slot can be empty.
In this case, we cannot do this check because pci_dev doesn't
exist, I think.

>
> - if yes, then we later check to see if the existing slot
> name matches the requested slot name from the hotplug
> driver.
>
> - if the hotplug driver is requesting a different name,
> then we use a new interface, pci_rename_slot() which
> will safely attempt to rename the slot without name
> collision.
>
> I'll send out the patch set soon, it would be great if you could
> test it for me, since I don't have systems with duplicate slot
> names.
>

Sure.

P.S.
I also don't have the system with duplicate slot names. So I use
the debug patch that emulates this kind of system for testing.

Thanks,
Kenji Kaneshige