[PATCH] Driver core: treat unregistered bus_types as having no devices

[Bjorn Helgaas <bhelgaas@google.com>]

A bus_type has a list of devices (klist_devices), but the list and the
subsys_private structure that contains it are not initialized until the
bus_type is registered with bus_register().

The panic/reboot path has fixups that look up devices in pci_bus_type.  If
we panic before registering pci_bus_type, the bus_type exists but the list
does not, so mach_reboot_fixups() trips over a null pointer and panics
again:

    mach_reboot_fixups
      pci_get_device
        ..
          bus_find_device(&pci_bus_type, ...)
            bus->p is NULL

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/base/bus.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 24eb078..6856303 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -290,7 +290,7 @@ int bus_for_each_dev(struct bus_type *bus, struct device *start,
 	struct device *dev;
 	int error = 0;
 
-	if (!bus)
+	if (!bus || !bus->p)
 		return -EINVAL;
 
 	klist_iter_init_node(&bus->p->klist_devices, &i,
@@ -324,7 +324,7 @@ struct device *bus_find_device(struct bus_type *bus,
 	struct klist_iter i;
 	struct device *dev;
 
-	if (!bus)
+	if (!bus || !bus->p)
 		return NULL;
 
 	klist_iter_init_node(&bus->p->klist_devices, &i,