On Mon, 2013-11-25 at 01:09 +0100, Rafael J. Wysocki wrote:
> Hi,
> 
> The following series of four patches (on top of current linux-pm.git/bleeding-edge)
> rework child device lookup in drivers/acpi/glue.c and related things:
> 
> [1/4] ACPI / bind: Simplify child device lookup
> [2/4] PCI/ ACPI: Use acpi_find_child_device() for child device lookup
> [3/4] ACPI / bind: Redefine acpi_get_child()
> [4/4] ACPI / bind: Redefine acpi_preset_companion()

This patchset caused the attached panic during boot on a system.
acpi_pci_find_device() called acpi_find_child_device() with
ACPI_COMPANION(dev->parent) being a NULL pointer when scanning bus 0xf.

This bus 0xf seems to be a chipset internal bus, which is not intended
for the OS to use.  Therefore, ACPI does not list its PCI bridge device.

# lspci -tv
   :
 +-[0000:0f]-+-08.0  Intel Corporation Ivytown QPI Link 0
 |           +-08.2  Intel Corporation Ivytown QPI Link 0
   :

However, pcibios_fixup_peer_bridges(), called from pci_subsys_init(),
finds this bus as it scans all the buses from 0 to pcibios_last_bus.
Hence, this dev->parent does not have an associated ACPI device object. 

Thanks,
-Toshi