On Mon, 13 Jan 2020, Andrey Konovalov wrote: > I've also found an issue, but I'm not sure if that is the bug in Raw > Gadget, or in the gadget layer (in the former case I'll add this fix > to v5 as well). What I believe I'm seeing is > __fput()->usb_gadget_unregister_driver()->usb_gadget_remove_driver()->gadget_unbind() > racing with dummy_timer()->gadget_setup(). In my case it results in > gadget_unbind() doing set_gadget_data(gadget, NULL), and then > gadget_setup() dereferencing get_gadget_data(gadget). > > Alan, does it look possible for those two functions to race? Should > this be prevented by the gadget layer, or should I use some kind of > locking in my gadget driver to prevent this? In your situation this race shouldn't happen, because before udc->driver->unbind() is invoked we call usb_gadget_disconnect(). If that routine succeeds -- which it always does under dummy-hcd -- then there can't be any more setup callbacks, because find_endpoint() will always return NULL (the is_active() test fails; see the various set_link_state* routines). So I don't see how you could have ended up with the race you describe. However, a real UDC might not be able to perform a disconnect under software control. In that case usb_gadget_disconnect() would not change the pullup state, and there would be a real possibility of a setup callback racing with an unbind callback. This seems like a genuine problem and I can't think of a solution offhand. What we would need is a way to tell the UDC driver to stop invoking gadget callbacks, _before_ the UDC driver's stop callback gets called. Maybe this should be merged into the pullup callback somehow. Alan Stern
