usbmon: fix tiny race exposed by the fastboot patches

usbmon registers the notifier chain, takes the bus lock and then goes to
scan the existing devices for hooking up.

Unfortunately, if usb_mon gets initialized while USB bus discovery is
going on, it's possible that usbmon gets a notifier on one cpu (which runs
without USB locks), and the scan is going on and also finds the new bus,
resulting in a double sysfs registration, which then produces a WARNING.

Pete Zaitcev did the bug diagnostics on this one

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/mon/mon_main.c b/drivers/usb/mon/mon_main.c
index 442d8076b201d10284c1928fdaa1a3891f5ae027..5e0ab4201c00894def56d3c182461173c89344c7 100644 (file)
--- a/drivers/usb/mon/mon_main.c
+++ b/drivers/usb/mon/mon_main.c
@@ -361,12 +361,12 @@ static int __init mon_init(void)
        }
        // MOD_INC_USE_COUNT(which_module?);
 
-       usb_register_notify(&mon_nb);
 
        mutex_lock(&usb_bus_list_lock);
        list_for_each_entry (ubus, &usb_bus_list, bus_list) {
                mon_bus_init(ubus);
        }
+       usb_register_notify(&mon_nb);
        mutex_unlock(&usb_bus_list_lock);
        return 0;