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 10:40:27 -0700
From:	Shuah Khan <shuahkhan@...il.com>
To:	Betty Dall <betty.dall@...com>
Cc:	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 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?

Thanks,
-- Shuah
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