linux-kernel - Re: [PATCH v4 03/15] PCI: prevent duplicate slot names

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Date:	Wed, 08 Oct 2008 15:00:07 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Alex Chiang <achiang@...com>
CC:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	jbarnes@...tuousgeek.org, kristen.c.accardi@...el.com,
	matthew@....cx
Subject: Re: [PATCH v4 03/15] PCI: prevent duplicate slot names

Alex Chiang wrote:

(snip.)

> diff --git a/drivers/pci/hotplug/pci_hotplug_core.c b/drivers/pci/hotplug/pci_hotplug_core.c
> index e00266b..b196ea1 100644
> --- a/drivers/pci/hotplug/pci_hotplug_core.c
> +++ b/drivers/pci/hotplug/pci_hotplug_core.c
> @@ -572,41 +572,32 @@ 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);
> -
>  	mutex_lock(&pci_hp_mutex);
> -	if (pci_slot->hotplug) {
> -		mutex_unlock(&pci_hp_mutex);
> -		dbg("%s: already claimed\n", __func__);
> -		pci_destroy_slot(pci_slot);
> -		return -EBUSY;
> +	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 think there still remain race condition. The situation I imagine
is as follows, though I might be misunderstanding something.

If pci_slot driver created pci_slot between pci_get_pci_slot() and
pci_create_slot() in pci_hp_register() in the hotplug driver's thread,
pci_rename_slot() would never be called and name specified by pci_slot
driver would be used instead of the one specified by hotplug driver.


> -void pci_update_slot_number(struct pci_slot *slot, int slot_nr)
> +void pci_renumber_slot(struct pci_slot *slot, int slot_nr)
>  {
> -	int name_count = 0;
>  	struct pci_slot *tmp;
>  
>  	down_write(&pci_bus_sem);
>  
>  	list_for_each_entry(tmp, &slot->bus->slots, list) {
>  		WARN_ON(tmp->number == slot_nr);
> -		if (!strcmp(kobject_name(&tmp->kobj), kobject_name(&slot->kobj)))
> -			name_count++;
> +		goto out;
>  	}
>  
> -	if (name_count > 1)
> -		printk(KERN_WARNING "pci_update_slot_number found %d slots with the same name: %s\n", name_count, kobject_name(&slot->kobj));
> -
>  	slot->number = slot_nr;
> +out:
>  	up_write(&pci_bus_sem);
>  }
> -EXPORT_SYMBOL_GPL(pci_update_slot_number);
> +EXPORT_SYMBOL_GPL(pci_renumber_slot);
>  

You changed exported symbol name. I think it should be made as
an another patch.

Thanks,
Kenji Kaneshige

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