ACPI: dock: fix opps after dock driver fails to initialize

The driver tests the dock_station pointer for nonnull
to check whether it has initialized properly. But in
some cases dock_station will be non-null after being
freed when driver init fails. Fix by zeroing the
pointer after freeing.
Signed-off-by: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/dock.c

@@ -715,6 +715,7 @@ static int dock_add(acpi_handle handle)
 	if (ret) {
 		printk(KERN_ERR PREFIX "Error %d registering dock device\n", ret);
 		kfree(dock_station);
+		dock_station = NULL;
 		return ret;
 	}
 	ret = device_create_file(&dock_device.dev, &dev_attr_docked);
@@ -722,6 +723,7 @@ static int dock_add(acpi_handle handle)
 		printk("Error %d adding sysfs file\n", ret);
 		platform_device_unregister(&dock_device);
 		kfree(dock_station);
+		dock_station = NULL;
 		return ret;
 	}
 	ret = device_create_file(&dock_device.dev, &dev_attr_undock);
@@ -730,6 +732,7 @@ static int dock_add(acpi_handle handle)
 		device_remove_file(&dock_device.dev, &dev_attr_docked);
 		platform_device_unregister(&dock_device);
 		kfree(dock_station);
+		dock_station = NULL;
 		return ret;
 	}
 	ret = device_create_file(&dock_device.dev, &dev_attr_uid);
@@ -739,6 +742,7 @@ static int dock_add(acpi_handle handle)
 		device_remove_file(&dock_device.dev, &dev_attr_undock);
 		platform_device_unregister(&dock_device);
 		kfree(dock_station);
+		dock_station = NULL;
 		return ret;
 	}
 
@@ -751,6 +755,7 @@ static int dock_add(acpi_handle handle)
 	dd = alloc_dock_dependent_device(handle);
 	if (!dd) {
 		kfree(dock_station);
+		dock_station = NULL;
 		ret = -ENOMEM;
 		goto dock_add_err_unregister;
 	}
@@ -779,6 +784,7 @@ static int dock_add(acpi_handle handle)
 	device_remove_file(&dock_device.dev, &dev_attr_uid);
 	platform_device_unregister(&dock_device);
 	kfree(dock_station);
+	dock_station = NULL;
 	return ret;
 }
 
@@ -813,6 +819,7 @@ static int dock_remove(void)
 
 	/* free dock station memory */
 	kfree(dock_station);
+	dock_station = NULL;
 	return 0;
 }