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

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Date:	Mon, 3 Dec 2012 13:59:52 -0700
From:	Shuah Khan <shuahkhan@...il.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Betty Dall <betty.dall@...com>, bhelgaas@...gle.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 1:00 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.

-- Shuah
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