Messages in this thread | | | Date | Fri, 03 Oct 2008 10:33:52 +0900 | From | Kenji Kaneshige <> | Subject | Re: [PATCH v3 02/14] PCI: prevent duplicate slot names |
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Alex Chiang wrote: > Hi Kenji-san, > > * Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>: >> Alex Chiang wrote: >>> * Kenji Kaneshige <kaneshige.kenji@jp.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'm sorry, I don't think I see the problem you are pointing out. > > If pci_get_pci_slot() finds a pci_slot, we do not modify > pci_bus->slots any further, so even if a new slot is created, it > shouldn't affect the pci_slot that we already found. > > I must be missing something, but I don't know what. Would you > mind explaining what you had in mind with your comment? >
Here is one of the example of the problem I imagine.
When pci_get_pci_slot() does NOT find a pci_slot, pci_hp_register() calls pci_create_slot(). If another hotplug driver creates slot between pci_get_pci_slot() and pci_create_slot(), hotplug member of pci_slot returned from pci_create_slot() is not NULL in the following code.
>> pci_slot = pci_create_slot(bus, slot_nr, name); >> if ((result = IS_ERR(pci_slot))) >> goto out;
In this case, we should return with -EBUSY. But because there is no check to see if pci->slot is NULL, pci_slot->hotplug will be overwritten with the new value.
Thanks, Kenji Kaneshige
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