[now this discussion has turned to usb gadget +cc Felipe Balbi, linux-usb, -cc Dave Jones, Ilya Zykov] On Tue, 2013-03-05 at 23:39 +0100, Jiri Slaby wrote: > On 03/05/2013 11:20 PM, Peter Hurley wrote: > > [--cc Alan Cox] > > > > On Tue, 2013-03-05 at 21:50 +0100, Sebastian Andrzej Siewior wrote: > >> * Peter Hurley | 2013-02-05 15:20:15 [-0500]: > >> > >>> Please re-test with your dummy_hcd/g_nokia testcase, although > >>> I'm not convinced that usb gadget is using tty_hangup() appropriately. > >>> tty drivers use this for async carrier loss coming from an IRQ > >>> which will be disabled if the tty has been shutdown. Does gserial > >>> prevent async hangup to a dead tty in a similar fashion? > >> > >> Not sure I understood. tty_hangup() is only called from within > >> gserial_disconnect() which calls right after usb_ep_disable(). After > >> usb_ep_disable() no further serial packets can be received until the > >> endpoints are re-enabled. This happens in gserial_connect(). > > > > That's why I asked. There are two potential issues: > > > > First, tty_hangup() is asynchronous -- ie., it returns immediately. It > > does not wait for the tty device to actually perform the hangup. So if > > the gadget layers start cleanup immediately after, expecting that they > > won't get a flurry of tty calls, that would be bad. > > Sorry, I missed what driver is this? g_serial. drivers/usb/gadget/u_serial.c > > tty_vhangup() is synchronous -- ie., you wait while it cleans up. This > > is what the usb serial core does on it's disconnect() method. But I > > didn't research further if the circumstances were the same. > > Even when tty_vhangup returns, it does not guarantee a closed tty. And > it also does not guarantee that any of tty->ops won't be called. The > latter is true only for devices that can be consoles. (For those, > file->ops are not redirected.) In that case one needs to wait for > port->count to become 0. Perhaps I was oversimplifying. But my point was I doubt usb gadget is conducting its teardown safely wrt tty. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
