Re: [PATCH] PCI/ACPI: do not reference a pci device after it has been released

From: Bjorn Helgaas
Date: Thu Apr 28 2022 - 11:59:05 EST

On Thu, Apr 28, 2022 at 04:28:53PM +0200, Greg Kroah-Hartman wrote:
> In acpi_get_pci_dev(), the debugging message for when a PCI bridge is
> not found uses a pointer to a pci device whose reference has just been
> dropped. The chance that this really is a device that is now been
> removed from the system is almost impossible to happen, but to be safe,
> let's print out the debugging message based on the acpi root device
> which we do have a valid reference to at the moment.

This code was added by 497fb54f578e ("ACPI / PCI: Fix NULL pointer
dereference in acpi_get_pci_dev() (rev. 2)"). Not sure if it's worth
a Fixes: tag.

acpi_get_pci_dev() is used by only five callers, three of which are
video/backlight related. I'm always skeptical of one-off interfaces
like this, but I don't know enough to propose any refactoring or other

I'll leave this for Rafael, but if I were applying I would silently
touch up the subject to match convention:

PCI/ACPI: Do not reference PCI device after it has been released

> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Len Brown <lenb@xxxxxxxxxx>
> Cc: linux-pci@xxxxxxxxxxxxxxx
> Cc: linux-acpi@xxxxxxxxxxxxxxx
> Reported-by: whitehat002 <hackyzh002@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
> drivers/acpi/pci_root.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 6f9e75d14808..ecda378dbc09 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -303,7 +303,8 @@ struct pci_dev *acpi_get_pci_dev(acpi_handle handle)
> * case pdev->subordinate will be NULL for the parent.
> */
> if (!pbus) {
> - dev_dbg(&pdev->dev, "Not a PCI-to-PCI bridge\n");
> + dev_dbg(&root->device->dev,
> + "dev %d, function %d is not a PCI-to-PCI bridge\n", dev, fn);

This should use "%02x.%d" to be consistent with the dev_set_name() in

> pdev = NULL;
> break;
> }
> --
> 2.36.0