tty: invert return values of tty_{,un}throttle_safe()

If tty_{,un}throttle_safe() returned true on success (similar to
*_trylock()), it would make the conditions in callers more obvious. So
perform the switch to these inverted values (and fix the callers).
Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230919085156.1578-8-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

@@ -253,7 +253,7 @@ static void n_tty_check_throttle(struct tty_struct *tty)
 		tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
 		if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
 			break;
-	} while (tty_throttle_safe(tty));
+	} while (!tty_throttle_safe(tty));
 
 	__tty_set_flow_change(tty, 0);
 }
@@ -282,7 +282,7 @@ static void n_tty_check_unthrottle(struct tty_struct *tty)
 			break;
 
 		n_tty_kick_worker(tty);
-	} while (tty_unthrottle_safe(tty));
+	} while (!tty_unthrottle_safe(tty));
 
 	__tty_set_flow_change(tty, 0);
 }

drivers/tty/tty_ioctl.c

@@ -124,16 +124,16 @@ EXPORT_SYMBOL(tty_unthrottle);
  *	conditions when throttling is conditional on factors evaluated prior to
  *	throttling.
  *
- *	Returns false if tty is throttled (or was already throttled)
+ *	Returns true if tty is throttled (or was already throttled)
  */
 bool tty_throttle_safe(struct tty_struct *tty)
 {
-	bool ret = false;
+	bool ret = true;
 
 	mutex_lock(&tty->throttle_mutex);
 	if (!tty_throttled(tty)) {
 		if (tty->flow_change != TTY_THROTTLE_SAFE)
-			ret = true;
+			ret = false;
 		else {
 			set_bit(TTY_THROTTLED, &tty->flags);
 			if (tty->ops->throttle)
@@ -154,16 +154,16 @@ bool tty_throttle_safe(struct tty_struct *tty)
  *	unthrottle due to race conditions when unthrottling is conditional
  *	on factors evaluated prior to unthrottling.
  *
- *	Returns false if tty is unthrottled (or was already unthrottled)
+ *	Returns true if tty is unthrottled (or was already unthrottled)
  */
 bool tty_unthrottle_safe(struct tty_struct *tty)
 {
-	bool ret = false;
+	bool ret = true;
 
 	mutex_lock(&tty->throttle_mutex);
 	if (tty_throttled(tty)) {
 		if (tty->flow_change != TTY_UNTHROTTLE_SAFE)
-			ret = true;
+			ret = false;
 		else {
 			clear_bit(TTY_THROTTLED, &tty->flags);
 			if (tty->ops->unthrottle)