linux-kernel - Re: [PATCH 1/3] msi: add forgotten pci_dev_put(pdev) to populate_msi

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Date:	Wed, 25 Sep 2013 15:08:05 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Veaceslav Falico <vfalico@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Neil Horman <nhorman@...driver.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/3] msi: add forgotten pci_dev_put(pdev) to populate_msi_sysfs()

[+cc Neil (he added this code in da8d1c8ba4), Greg]

On Mon, Sep 16, 2013 at 7:47 PM, Veaceslav Falico <vfalico@...hat.com> wrote:
> Before trying to kobject_init_and_add(), we add a reference to pdev via
> pci_dev_get(pdev). However, if it fails to init and/or add the kobject, we
> don't return it back - even on out_unroll.
>
> Fix this by adding pci_dev_put(pdev) before going to unrolling section.
>
> CC: Bjorn Helgaas <bhelgaas@...gle.com>
> CC: linux-pci@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> Signed-off-by: Veaceslav Falico <vfalico@...hat.com>
> ---
>  drivers/pci/msi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index d5f90d6..14bf578 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -534,8 +534,10 @@ static int populate_msi_sysfs(struct pci_dev *pdev)
>                 pci_dev_get(pdev);
>                 ret = kobject_init_and_add(kobj, &msi_irq_ktype, NULL,
>                                      "%u", entry->irq);
> -               if (ret)
> +               if (ret) {
> +                       pci_dev_put(pdev);
>                         goto out_unroll;
> +               }
>
>                 count++;
>         }

I don't understand why this code does the pci_dev_get() in the first
place.  The pdev->msi_list of msi_desc structs is private to the
pci_dev, and even without bumping the refcount, there should be no way
for the pci_dev to be freed before the msi_desc.

I also don't understand this nearby code (the same pattern appears in
free_msi_irqs()):

    out_unroll:
        list_for_each_entry(entry, &pdev->msi_list, list) {
                if (!count)
                        break;
                kobject_del(&entry->kobj);
                kobject_put(&entry->kobj);
                count--;
        }

Why do we call kobject_del() here?  The kobject_put() will call
kobject_del() anyway, so it looks redundant.
Documentation/kobject.txt says kobject_del() must be called explicitly
to break a circular reference, but I don't think we have that here.

Also, I think it is incorrect that free_msi_irqs() does this:

                if (entry->kobj.parent) {
                        kobject_del(&entry->kobj);
                        kobject_put(&entry->kobj);
                }

                list_del(&entry->list);
                kfree(entry);

I think the "kfree(entry)" should be in msi_kobj_release() instead.

Bjorn
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