linux-kernel - Re: 2.6.25-rc8-mm1 panic in rpaphp_register

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Date:	Wed, 16 Apr 2008 17:45:16 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alex Chiang <achiang@...com>
Cc:	Badari Pulavarty <pbadari@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.25-rc8-mm1 panic in rpaphp_register_slot()


On Tue, 2008-04-15 at 21:17 -0600, Alex Chiang wrote:
> Hi Ben,
> 
> Could you take a look at this patch and tell me what I'm doing
> wrong?

Hrm, I'll have a look but I'd need some context first... This is to fix
a problem introduced by another serie of patches ? Can you give me some
pointers here ?

The pSeries PCI stuff can be tricky so I'll need some time tomorrow to
context switch and remind myself of everything involved :-) So I'd like
to make sure by that time, I have all the elements.

Thanks,
Ben.

> Thanks.
> 
> /ac
> 
> * Alex Chiang <achiang@...com>:
> > Hi Badari,
> > 
> > > > > pci_hotplug: PCI Hot Plug PCI Core version: 0.5
> > > > > rpaphp: RPA HOT Plug PCI Controller Driver version: 0.1
> > > > > rpaphp_register_slot registering slot:path[/pci@...000020000003/pci@2,4] index[22010003], name[U787E.001.AAA3015-P2-C1] pdomain[22010003] type[16]
> > > > > Unable to handle kernel paging request for data at address 0x00000070
> > > > 
> > > > Hrm, this is a little more information, but still not quite
> > > > enough. I'm going to take a stab in the dark and say I'm probably
> > > > doing something wrong on this line, maybe dereferencing a pointer
> > > > incorrectly:
> > > > 
> > > >         retval = pci_hp_register(php_slot, slot->bus,
> > > > 				 PCI_SLOT(PCI_DN(slot->dn->child)->devfn));
> > > 
> > > Sorry. I thought you knew this already. Disassembly clearly showed
> > > that slot->dn->child is NULL. 
> > > 
> > > I confirmed it by adding printk also.
> > 
> > This patch is a complete guess on my part (since I've not been
> > able to understand pseries architecture) but I think it should
> > fix your issue.
> > 
> > Can you give it a try and let me know? It applies on top of the
> > -mm tree that includes my physical pci_slot series.
> > 
> > Also, I'm hoping Linas will speak up and let me know what the
> > real answer might be. ;)
> > 
> > Thanks.
> > 
> > /ac
> > 
> > From: Alex Chiang <achiang@...com>
> > Subject: rpaphp: correctly call pci_hp_register for empty PCI slots
> > 
> > Unpopulated device_node slots do not have children, and
> > attempting to dereference them will result in a panic.
> > 
> > Instead, attempt to derive the PCI slot number from the bus
> > itself, and failing that, default to 0.
> > 
> > Signed-off-by: Alex Chiang <achiang@...com>
> > ---
> > diff --git a/drivers/pci/hotplug/rpaphp_slot.c b/drivers/pci/hotplug/rpaphp_slot.c
> > index 0d4cfc7..91ce6a6 100644
> > --- a/drivers/pci/hotplug/rpaphp_slot.c
> > +++ b/drivers/pci/hotplug/rpaphp_slot.c
> > @@ -121,6 +121,7 @@ int rpaphp_register_slot(struct slot *slot)
> >  {
> >  	struct hotplug_slot *php_slot = slot->hotplug_slot;
> >  	int retval;
> > +	int slot_nr;
> >  
> >  	dbg("%s registering slot:path[%s] index[%x], name[%s] pdomain[%x] type[%d]\n", 
> >  		__FUNCTION__, slot->dn->full_name, slot->index, slot->name, 
> > @@ -132,8 +133,11 @@ int rpaphp_register_slot(struct slot *slot)
> >  		return -EAGAIN;
> >  	}	
> >  
> > -	retval = pci_hp_register(php_slot, slot->bus,
> > -				 PCI_SLOT(PCI_DN(slot->dn->child)->devfn));
> > +	if (slot->bus->self)
> > +		slot_nr = PCI_SLOT(slot->bus->self->devfn);
> > +	else
> > +		slot_nr = 0;
> > +	retval = pci_hp_register(php_slot, slot->bus, slot_nr);
> >  	if (retval) {
> >  		err("pci_hp_register failed with error %d\n", retval);
> >  		return retval;
> > --
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> > 

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