[PATCH 2/2] driver-core: do not register a driver with bus_type not registered

[Dave Young <hidave.darkstar@gmail.com>]

If the bus_type is not registerd, driver_register to that bus will cause oops.

I found this bug when test built-in usb serial drivers (ie. aircable driver)
with 'nousb' cmdline params. 

In this patch:
1. set the bus->p=NULL when bus_register failed and unregisterd.
2. if bus->p is NULL, driver_register BUG_ON will be triggered.

Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
---
drivers/base/bus.c    |    2 ++
drivers/base/driver.c |    2 ++
2 files changed, 4 insertions(+)

diff -uprN a/drivers/base/bus.c b/drivers/base/bus.c
--- a/drivers/base/bus.c	2009-02-14 20:47:24.441149465 +0800
+++ b/drivers/base/bus.c	2009-02-14 20:49:42.350149362 +0800
@@ -932,6 +932,7 @@ bus_uevent_fail:
 	kset_unregister(&bus->p->subsys);
 	kfree(bus->p);
 out:
+	bus->p = NULL;
 	return retval;
 }
 EXPORT_SYMBOL_GPL(bus_register);
@@ -953,6 +954,7 @@ void bus_unregister(struct bus_type *bus
 	bus_remove_file(bus, &bus_attr_uevent);
 	kset_unregister(&bus->p->subsys);
 	kfree(bus->p);
+	bus->p = NULL;
 }
 EXPORT_SYMBOL_GPL(bus_unregister);
 
diff -uprN a/drivers/base/driver.c b/drivers/base/driver.c
--- a/drivers/base/driver.c	2009-02-14 20:47:38.048149854 +0800
+++ b/drivers/base/driver.c	2009-02-14 20:47:50.692141034 +0800
@@ -216,6 +216,8 @@ int driver_register(struct device_driver
 	int ret;
 	struct device_driver *other;
 
+	BUG_ON(!drv->bus->p);
+
 	if ((drv->bus->probe && drv->probe) ||
 	    (drv->bus->remove && drv->remove) ||
 	    (drv->bus->shutdown && drv->shutdown))