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Subjectpcibios_scanned needs to be set in ACPI? (was Re: 2.6.25-rc5: Reported regressions from 2.6.24)
On Wed, Mar 12, 2008 at 01:32:05PM -0700, Greg KH wrote:
> On Wed, Mar 12, 2008 at 01:01:15PM -0700, Linus Torvalds wrote:
> >
> >
> > On Tue, 11 Mar 2008, Rafael J. Wysocki wrote:
> >
> > >
> > > In Guennadi says that
> > > reverting
> > >
> > > commit fd7d1ced29e5beb88c9068801da7a362606d8273
> > > Author: Greg Kroah-Hartman <>
> > > Date: Tue May 22 22:47:54 2007 -0400
> > >
> > > PCI: make pci_bus a struct device
> > >
> > > fixes the problem for him (this seems to be yet another reboot/poweroff IOW).
> >
> > Ahh, I thought this was done already, but nope, my PCI pull from Greg
> > didn't contain the revert.
> >
> > Greg? I know you must be aware of the problem, because you replied to the
> > email at some point. Wazzup?
> I'm still trying to figure out why his is the only machine having
> problems with this. I think it's an acpi "we walk the list of pci
> devices twice" type thing, but don't know yet.

Ok, I think I got it. And it looks like an ACPI bug, but one that we
might have been ignoring for a long time...

In looking at the log files at boot, we see that we are using ACPI to
find the PCI devices:

ACPI: PCI Interrupt Routing Table [\_SB_.PCI0._PRT]

Followed by a lot of kobjects for pci devices being added, including
this root bus:
kobject: '0000:01:00.0' (c7c978cc): kobject_add_internal: parent: '0000:00:01.0', set: 'devices'
kobject: '0000:01:00.0' (c7c978cc): kobject_uevent_env
kobject: '0000:01:00.0' (c7c978cc): fill_kobj_path: path = '/devices/pci0000:00/0000:00:01.0/0000:01:00.0'
kobject: '0000:01' (c7c35900): kobject_add_internal: parent: 'pci_bus', set: 'devices'
kobject: '0000:01' (c7c35900): kobject_uevent_env
kobject: '0000:01' (c7c35900): fill_kobj_path: path = '/class/pci_bus/0000:01'

All is fine, until later on we decide to fallback to the "old" style of
PCI: Probing PCI hardware
kobject (c7c35900): tried to init an initialized object, something is seriously wrong.
Pid: 1, comm: swapper Not tainted 2.6.25-rc2-testpm #30
[<c01ea0e9>] kobject_init+0x89/0x90
[<c025094e>] device_initialize+0x1e/0x90
[<c025119b>] device_register+0xb/0x20
[<c01f3fd8>] pci_bus_add_devices+0x98/0x140
[<c030aff7>] ? pcibios_scan_root+0x27/0xa0
[<c03f69d0>] pci_legacy_init+0x50/0xf0
[<c03db5c2>] kernel_init+0x132/0x310
[<c010303a>] ? ret_from_fork+0x6/0x1c
[<c03db490>] ? kernel_init+0x0/0x310
[<c03db490>] ? kernel_init+0x0/0x310
[<c0103d3f>] kernel_thread_helper+0x7/0x18
kobject: '0000:01' (c7c35900): kobject_add_internal: parent: 'pci_bus', set: 'devices'

This shows that we are trying to register the exact same kobject that we
had already previously registered. Not nice...

Now we have a check in the pci bus code to not register anything that we
had already registered in the past:

list_for_each_entry(dev, &bus->devices, bus_list) {
* Skip already-present devices (which are on the
* global device list.)
if (!list_empty(&dev->global_list))
retval = pci_bus_add_device(dev);

But, in redoing the pci list logic (coming in .26 and in -mm and -next)
I realized that this wasn't a real check, as this list is just a
"shadow" list that some types of pci probing never set up.

So that explains why the warning we get when trying to register a device
multiple times in the kobject core.

But why does this happen in the first place?

The code in arch/x86/pci/legacy.c::pci_legacy_init() checks the
pcibios_scanned flag to determine if we had already scanned the PCI bus.
Which we did in the ACPI code, right?

So, Len, shouldn't we be setting this flag in the ACPI core if we had
already scanned the pci bus there?

I can fix this problem by putting the check in the pci core in
pci_bus_add_devices() like we have done in -next, but I think that we
also need to do something in ACPI as well.

Guennadi, could you test the -next kernel tree to see if the logic there
solves this issue for you?


greg k-h

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