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

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Message-ID: <48C885B4.2070200@jp.fujitsu.com>
Date:	Thu, 11 Sep 2008 11:43:00 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Alex Chiang <achiang@...com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	jbarnes@...tuousgeek.org, kristen.c.accardi@...el.com,
	matthew@....cx
Subject: Re: [PATCH 02/13] PCI: prevent duplicate slot names

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


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