tty: throttling race fix

[linux-2.6-block.git] / drivers / char / tty_ioctl.c

diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index 6f4c7d0a53bf36bc6ff28afeadca4720704e459f..2401dbcbee9c170e2efdfe2bfbf474c61fbe2acc 100644 (file)
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -97,14 +97,19 @@ EXPORT_SYMBOL(tty_driver_flush_buffer);
  *     @tty: terminal
  *
  *     Indicate that a tty should stop transmitting data down the stack.
+ *     Takes the termios mutex to protect against parallel throttle/unthrottle
+ *     and also to ensure the driver can consistently reference its own
+ *     termios data at this point when implementing software flow control.
  */
 
 void tty_throttle(struct tty_struct *tty)
 {
+       mutex_lock(&tty->termios_mutex);
        /* check TTY_THROTTLED first so it indicates our state */
        if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
            tty->ops->throttle)
                tty->ops->throttle(tty);
+       mutex_unlock(&tty->termios_mutex);
 }
 EXPORT_SYMBOL(tty_throttle);
 
@@ -113,13 +118,21 @@ EXPORT_SYMBOL(tty_throttle);
  *     @tty: terminal
  *
  *     Indicate that a tty may continue transmitting data down the stack.
+ *     Takes the termios mutex to protect against parallel throttle/unthrottle
+ *     and also to ensure the driver can consistently reference its own
+ *     termios data at this point when implementing software flow control.
+ *
+ *     Drivers should however remember that the stack can issue a throttle,
+ *     then change flow control method, then unthrottle.
  */
 
 void tty_unthrottle(struct tty_struct *tty)
 {
+       mutex_lock(&tty->termios_mutex);
        if (test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
            tty->ops->unthrottle)
                tty->ops->unthrottle(tty);
+       mutex_unlock(&tty->termios_mutex);
 }
 EXPORT_SYMBOL(tty_unthrottle);