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? > 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. -- js suse labs -- 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
