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Commit e91e52e4 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

n_tty: Fix stuck throttled driver 



As noted in the following comment:

  /* FIXME: there is a tiny race here if the receive room check runs
     before the other work executes and empties the buffer (upping
     the receiving room and unthrottling. We then throttle and get
     stuck. This has been observed and traced down by Vincent Pillet/
     We need to address this when we sort out out the rx path locking */

Use new safe throttle/unthrottle functions to re-evaluate conditions
if interrupted by the complement flow control function.

Reported-by: default avatarVincent Pillet <vincentx.pillet@intel.com>
Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 70bc1264

drivers/tty/n_tty.c

+17 −11
Original line number Diff line number Diff line
@@ -1468,14 +1468,14 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp, 
	 * mode.  We don't want to throttle the driver if we're in

	 * canonical mode and don't have a newline yet!

	 */

	if (tty->receive_room < TTY_THRESHOLD_THROTTLE)

		tty_throttle(tty);



        /* FIXME: there is a tiny race here if the receive room check runs

           before the other work executes and empties the buffer (upping

           the receiving room and unthrottling. We then throttle and get

           stuck. This has been observed and traced down by Vincent Pillet/

           We need to address this when we sort out out the rx path locking */

	while (1) {

		tty_set_flow_change(tty, TTY_THROTTLE_SAFE);

		if (tty->receive_room >= TTY_THRESHOLD_THROTTLE)

			break;

		if (!tty_throttle_safe(tty))

			break;

	}

	__tty_set_flow_change(tty, 0);

}



int is_ignored(int sig)
@@ -1944,11 +1944,17 @@ do_it_again: 
		 * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,

		 * we won't get any more characters.

		 */

		if (n_tty_chars_in_buffer(tty) <= TTY_THRESHOLD_UNTHROTTLE) {

		while (1) {

			tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);

			if (n_tty_chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)

				break;

			if (!tty->count)

				break;

			n_tty_set_room(tty);

			if (tty->count)

				tty_unthrottle(tty);

			if (!tty_unthrottle_safe(tty))

				break;

		}

		__tty_set_flow_change(tty, 0);



		if (b - buf >= minimum)

			break;