linux-kernel - Re: [PATCH v3 02/14] PCI: prevent duplicate slot names

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Date:	Thu, 02 Oct 2008 11:47:51 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Alex Chiang <achiang@...com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	jbarnes@...tuousgeek.org, kristen.c.accardi@...el.com,
	matthew@....cx
Subject: Re: [PATCH v3 02/14] PCI: prevent duplicate slot names

Alex-san,

Alex Chiang wrote:
> * Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>:
>> Kenji Kaneshige wrote:
>>> Hi Alex-san,
>>>
>>> Here is one comment, though I have not finished reviewing/testing
>>> your patches yet (sorry for the delay).
>>>
>>> Alex Chiang wrote:
>>>
>>> (snip.)
>>>
>>>> diff --git a/drivers/pci/hotplug/pci_hotplug_core.c  
>>>> b/drivers/pci/hotplug/pci_hotplug_core.c
>>>> index 3e37d63..46802dc 100644
>>>> --- a/drivers/pci/hotplug/pci_hotplug_core.c
>>>> +++ b/drivers/pci/hotplug/pci_hotplug_core.c
>>>> @@ -570,39 +570,32 @@ int pci_hp_register(struct hotplug_slot *slot,  
>>>> struct pci_bus *bus, int slot_nr,
>>>>          return -EINVAL;
>>>>      }
>>>>  -    /* Check if we have already registered a slot with the same 
>>>> name. */
>>>> -    if (get_slot_from_name(name))
>>>> -        return -EEXIST;
>>>> -
>>>>      /*
>>>> -     * 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.
>>>> +     * Look for existing slot. If we find it, and it was created by a
>>>> +     * slot detection driver (ie, doesn't have a ->hotplug()) then we
>>>> +     * allow the hotplug driver calling us to rename the slot if  
>>>> desired.
>>>> +     *
>>>> +     * Otherwise, create the slot and carry on with life.
>>>>       */
>>>> -    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;
>>>> +    pci_slot = pci_get_pci_slot(bus, slot_nr);
>>> The pci_get_pci_slot() function refers pci_bus->slots list, so it
>>> should be called with pci_bus_sem semaphore held as pci_create_slot()
>>> does, or pci_bus_sem semaphore should be held by pci_get_pci_slot()
>>> itself.
> 
> Yes, I've changed pci_get_pci_slot() to acquire the pci_bus_sem
> semaphore.
> 
> Thank you for pointing this out.
> 
> It will be fixed in v4 of this patch series, which I will send
> out after I receive the rest of your review comments.
> 

I noticed that changing pci_get_pci_slot() to acquire the pci_bus_sem
might be not enough. If slot was created between pci_get_pci_slot() and
pci_create_slot() by another thread in the following code, something
wrong would happen I think.

        pci_slot = pci_get_pci_slot(bus, slot_nr);
        if (pci_slot) {
                if (pci_slot->hotplug) {
                        result = -EBUSY;
                        goto err;
                }

                if (strcmp(kobject_name(&pci_slot->kobj), name))
                        if ((result = pci_rename_slot(pci_slot, name)))
                                goto err;
        } else {
                pci_slot = pci_create_slot(bus, slot_nr, name);
                if ((result = IS_ERR(pci_slot)))
                        goto out;
        }

I've finished reviewing and testing your patches. The rest of your
patch looks good to me. Of course, we must not forget the comment
from Taku Izumi.

Thanks,
Kenji Kaneshige



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