On 09/21/2012 07:59 AM, Bjorn Helgaas wrote:
> On Thu, Sep 20, 2012 at 2:38 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
>> On Tue, Aug 28, 2012 at 8:43 AM, Jiang Liu <liuj97@xxxxxxxxx> wrote:
>>> Following code has a race window between pci_find_bus() and pci_get_slot()
>>> if PCI hotplug operation happens between them which removes the pci_bus.
>>> So use PCI hotplug safe interface pci_get_domain_bus_and_slot() instead,
>>> which also reduces code complexity.
>>>
>>> struct pci_bus *pci_bus = pci_find_bus(domain, busno);
>>> struct pci_dev *pci_dev = pci_get_slot(pci_bus, devfn);
>>>
>>> Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxx>
>>> ---
>>> drivers/pci/iov.c | 8 ++------
>>> 1 file changed, 2 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>>> index aeccc91..b0fe771 100644
>>> --- a/drivers/pci/iov.c
>>> +++ b/drivers/pci/iov.c
>>> @@ -152,15 +152,11 @@ failed1:
>>> static void virtfn_remove(struct pci_dev *dev, int id, int reset)
>>> {
>>> char buf[VIRTFN_ID_LEN];
>>> - struct pci_bus *bus;
>>> struct pci_dev *virtfn;
>>> struct pci_sriov *iov = dev->sriov;
>>>
>>> - bus = pci_find_bus(pci_domain_nr(dev->bus), virtfn_bus(dev, id));
>>> - if (!bus)
>>> - return;
>>> -
>>> - virtfn = pci_get_slot(bus, virtfn_devfn(dev, id));
>>> + virtfn = pci_get_domain_bus_and_slot(pci_domain_nr(dev->bus),
>>> + virtfn_bus(dev, id), virtfn_devfn(dev, id));
>>> if (!virtfn)
>>> return;
>>>
>>
>> Hi,
>>
>> This one cause IOV regression, when remove bridge with pci devices under that.
>>
>> in that case, VFs are stopped before PF, so they are not in device
>> tree anymore.
>> so pci_get_domain_bus_and_slot will not find those VFs.
>>
>> So the reference to PF is not released. Also vit_bus may not be released too.
>>
>> So you have to rework
>> pci_get_domain_bus_and_slot to make it work on pci devices get stopped only.
>>
>> or just drop this from the tree.
>
> pci_find_bus() is a broken interface (because there's no reference
> counting or safety with respect to hot-plug), and if the design
> depends on it, that means the design is broken, too. I don't think
> reworking pci_get_domain_bus_and_slot() is the right answer.
>
> It's not clear to me why we need the split between stopping and
> removing devices. That split leads to these zombie devices that have
> been stopped and are no longer findable by bus_find_device() (which is
> used by pci_get_domain_bus_and_slot()), but still "exist" in some
> fashion until they're removed. It's unreasonable for random PCI and
> driver code to have to worry about that zombie state.
>
> I'll revert this patch for now to fix the regression. Of course, that
> means we will still have the old problem of using the unsafe
> pci_find_bus().
Hi Bjorn,
I'm working on to enhance unsafe calling of pci_find_bus().
--Gerry
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