linux-kernel - Re: [PATCH] PCI AER: pci_get_domain_bus_and_slot() call missing required pci_dev

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Date:	Mon, 7 Jan 2013 11:46:53 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Shuah Khan <shuahkhan@...il.com>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Betty Dall <betty.dall@...com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, wangyijing@...wei.com,
	jiang.liu@...wei.com
Subject: Re: [PATCH] PCI AER: pci_get_domain_bus_and_slot() call missing
 required pci_dev_put()

On Mon, Dec 3, 2012 at 1:59 PM, Shuah Khan <shuahkhan@...il.com> wrote:
> On Mon, Dec 3, 2012 at 1:00 PM, Alex Williamson
> <alex.williamson@...hat.com> wrote:
>> On Mon, 2012-12-03 at 12:48 -0700, Alex Williamson wrote:
>>> On Mon, 2012-12-03 at 10:40 -0700, Shuah Khan wrote:
>>> > On Mon, Dec 3, 2012 at 9:37 AM, Betty Dall <betty.dall@...com> wrote:
>>> > > The function aer_recover_queue() makes a call to pci_get_domain_bus_and_slot().
>>> > > That function is documented to require that the caller decrement the
>>> > > reference count by calling pci_dev_put(). This patch adds the missing
>>> > > call to pci_dev_put().
>>> > >
>>> > > Signed-off-by: Betty Dall <betty.dall@...com>
>>> > > ---
>>> > >  drivers/pci/pcie/aer/aerdrv_core.c |    1 +
>>> > >  1 files changed, 1 insertions(+), 0 deletions(-)
>>> > >
>>> > > diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
>>> > > index af4e31c..43caf53 100644
>>> > > --- a/drivers/pci/pcie/aer/aerdrv_core.c
>>> > > +++ b/drivers/pci/pcie/aer/aerdrv_core.c
>>> > > @@ -616,6 +616,7 @@ static void aer_recover_work_func(struct work_struct *work)
>>> > >                         continue;
>>> > >                 }
>>> > >                 do_recovery(pdev, entry.severity);
>>> > > +               pci_dev_put(pdev);
>>> >
>>> > Are you sure pci_get_domain_bus_and_slot() does indeed increment the
>>> > reference count? I see that in the comments right above the
>>> > definition.
>>> >
>>> > pci_dev_get() does that for sure. I see a call trace of
>>> >
>>> > pci_dev_get() -> get_device() -> kobj_to_dev(kobject_get(&dev->kobj)  etc.
>>> >
>>> > and kref_get() finally incrementing the
>>> >
>>> > static inline void kref_get(struct kref *kref)
>>> > {
>>> >         WARN_ON(!atomic_read(&kref->refcount));
>>> >         atomic_inc(&kref->refcount);
>>> > }
>>> >
>>> > However, I could not find any evidence that
>>> > pci_get_domain_bus_and_slot() does that. I see
>>> > pci_get_domain_bus_and_slot() calling pci_domain_nr() and there are
>>> > several architecture specific defines for pci_domain_nr(). It is not
>>> > clear to me where does refcount get incremented from
>>> > pci_get_domain_bus_and_slot() is called.
>>> >
>>> > What am I missing?
>>>
>>> Trace back the for_each_pci_dev()
>>>
>>> for_each_pci_dev
>>>  -> pci_get_device
>>>   -> pci_get_subsys
>>>    -> pci_get_dev_by_id
>>>     -> bus_find_device
>>>      -> get_device()
>>>
>>> The real question is how many places do we call for_each_pci_dev()
>>> without a put.  It seems like pci_get_domain_bus_and_slot() doesn't even
>>> get it right since it should include a put of the non-matched devices.
>>
>> My bad, pci_get_dev_by_id() does a put on the previous devices, keeping
>> the counts in order.  Thanks,
>>
>> Alex
>>
> Thanks Alex.
>
> Betty,
>
> You have my
>
> Reviewed-by: Shuah Khan <shuah.khan@...com>
>
> Also if you think this is applicable to stable as well, could you
> please CC it for stable.

Thanks, Betty!  I'll merge this as a fix for v3.8.

Did you find this by inspection, or can you trigger some bad behavior?

Bjorn
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