Re: 2.6.25-rc8-mm1 panic in rpaphp_register_slot()

[Alex Chiang <achiang@hp.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@800000020000003/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@hp.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@hp.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;