PCI: acpiphp: cleanup notify handler on all root bridges

During the development of the physical PCI slot patch series, Gary Hade
kept on reporting strange oopses due to interactions between pci_slot
and acpiphp.

	http://lkml.org/lkml/2007/11/28/319

find_root_bridges() unconditionally installs
handle_hotplug_event_bridge() as an ACPI_SYSTEM_NOTIFY handler for all
root bridges.

However, during module cleanup, remove_bridge() will only remove the
notify handler iff the root bridge had a hot-pluggable slot directly
underneath. That is:

	root bridge -> hotplug slot

But, if the topology looks like either of the following:

	root bridge -> non-hotplug slot
	root bridge -> p2p bridge -> hotplug slot

Then we currently do not remove the notify handler from that root
bridge.

This can cause a kernel oops if we modprobe acpiphp later and it gets
loaded somewhere else in memory. If the root bridge then receives a
hotplug event, it will then attempt to call a stale, non-existent notify
handler and we blow up.

Much thanks goes to Gary Hade for his persistent debugging efforts.
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Gary Hade <garyhade@us.ibm.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/hotplug/acpiphp_glue.c

@@ -700,9 +700,10 @@ cleanup_p2p_bridge(acpi_handle handle, u32 lvl, void *context, void **rv)
 	acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, (u32)1,
 				cleanup_p2p_bridge, NULL, NULL);
 
-	if (!(bridge = acpiphp_handle_to_bridge(handle)))
-		return AE_OK;
-	cleanup_bridge(bridge);
+	bridge = acpiphp_handle_to_bridge(handle);
+	if (bridge)
+		cleanup_bridge(bridge);
+
 	return AE_OK;
 }
 
@@ -715,9 +716,19 @@ static void remove_bridge(acpi_handle handle)
 	acpi_walk_namespace(ACPI_TYPE_DEVICE, handle,
 				(u32)1, cleanup_p2p_bridge, NULL, NULL);
 
+	/*
+	 * On root bridges with hotplug slots directly underneath (ie,
+	 * no p2p bridge inbetween), we call cleanup_bridge(). 
+	 *
+	 * The else clause cleans up root bridges that either had no
+	 * hotplug slots at all, or had a p2p bridge underneath.
+	 */
 	bridge = acpiphp_handle_to_bridge(handle);
 	if (bridge)
 		cleanup_bridge(bridge);
+	else
+		acpi_remove_notify_handler(handle, ACPI_SYSTEM_NOTIFY,
+					   handle_hotplug_event_bridge);
 }
 
 static struct pci_dev * get_apic_pci_info(acpi_handle handle)