> Is there a mechanism preventing a different thread from running > n_tty_read between n_tty_receive_buf finding receive_room to be below > the threshold and tty_throttle being called? If not then isn't there a > race condition when the following happens: n_tty_receive is single threaded and is going to get run in preference to user threads. > 1. n_tty_receive_buf fills up the buffer so that the free space > is below TTY_THRESHOLD_THROTTLE > 2. n_tty_receive_buf comes to the check at the end and decide > that it needs to call tty_throttle > 3. Thread rescheduling happens and a different thread runs > n_tty_read which empties the buffer > 4. After emptying the buffer n_tty_read calls tty_unthrottle, > which does nothing as the throttling bit isn't set > 5. The n_tty_receive_buf thread is executed again, calling > tty_throttle, causing throttling, but with an empty buffer. > > Or have I not understood a complexity in the interactions within n_tty.c? Looks possible - historically it would have been safe but not any more. The scenario I think would have to be two thread of execution in parallel on two processors at the same moment and with near perfect timing but I don't see why it can't happen. Alan -- 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
