On Wed, 22 Sep 2010, Michal Nazarewicz wrote: > This commit fixes a possible race condition in IDC class when > usb_del_udc() is called concurrently to > usb_gadget_register_driver() or usb_gadget_unregister_driver(). > > * NOT FOR MERGING, NOT TESTED, NOT EVEN COMPILED * > After more thought I came up with a scheme where usage of atomic > operations (xchg and cmpxchg) is enough to guarantee correctness. > > The idea is that the driver field can have additional value: > &udc_claimed. This value means that usb_del_udc(), > usb_gadget_register_driver() or usb_gadget_unregister_driver() does > something with the UDC. So basically, UDC can be in either of three > states: free, busy or claimed where claimed means the above. > > usb_gadget_register_driver() treats claimed UDCs as busy, > usb_gadget_unregister_driver() as ones of no interest, and > usb_del_udc() waits till the UDC is unclaimed. Fancy coding schemes like this, in order to avoid proper locking, are incredibly difficult to do correctly. It's just not worth it. Don't try to be fancy; simply use a lock. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
