1 files changed, 83 insertions, 37 deletions

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index d58b92cc187c..3500d4114147 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -106,6 +106,7 @@ void tty_throttle(struct tty_struct *tty)
 	if (!test_and_set_bit(TTY_THROTTLED, &tty->flags) &&
 	    tty->ops->throttle)
 		tty->ops->throttle(tty);
+	tty->flow_change = 0;
 	mutex_unlock(&tty->termios_mutex);
 }
 EXPORT_SYMBOL(tty_throttle);
@@ -129,11 +130,74 @@ void tty_unthrottle(struct tty_struct *tty)
 	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
 	    tty->ops->unthrottle)
 		tty->ops->unthrottle(tty);
+	tty->flow_change = 0;
 	mutex_unlock(&tty->termios_mutex);
 }
 EXPORT_SYMBOL(tty_unthrottle);
 
 /**
+ *	tty_throttle_safe	-	flow control
+ *	@tty: terminal
+ *
+ *	Similar to tty_throttle() but will only attempt throttle
+ *	if tty->flow_change is TTY_THROTTLE_SAFE. Prevents an accidental
+ *	throttle due to race conditions when throttling is conditional
+ *	on factors evaluated prior to throttling.
+ *
+ *	Returns 0 if tty is throttled (or was already throttled)
+ */
+
+int tty_throttle_safe(struct tty_struct *tty)
+{
+	int ret = 0;
+
+	mutex_lock(&tty->termios_mutex);
+	if (!test_bit(TTY_THROTTLED, &tty->flags)) {
+		if (tty->flow_change != TTY_THROTTLE_SAFE)
+			ret = 1;
+		else {
+			set_bit(TTY_THROTTLED, &tty->flags);
+			if (tty->ops->throttle)
+				tty->ops->throttle(tty);
+		}
+	}
+	mutex_unlock(&tty->termios_mutex);
+
+	return ret;
+}
+
+/**
+ *	tty_unthrottle_safe	-	flow control
+ *	@tty: terminal
+ *
+ *	Similar to tty_unthrottle() but will only attempt unthrottle
+ *	if tty->flow_change is TTY_UNTHROTTLE_SAFE. Prevents an accidental
+ *	unthrottle due to race conditions when unthrottling is conditional
+ *	on factors evaluated prior to unthrottling.
+ *
+ *	Returns 0 if tty is unthrottled (or was already unthrottled)
+ */
+
+int tty_unthrottle_safe(struct tty_struct *tty)
+{
+	int ret = 0;
+
+	mutex_lock(&tty->termios_mutex);
+	if (test_bit(TTY_THROTTLED, &tty->flags)) {
+		if (tty->flow_change != TTY_UNTHROTTLE_SAFE)
+			ret = 1;
+		else {
+			clear_bit(TTY_THROTTLED, &tty->flags);
+			if (tty->ops->unthrottle)
+				tty->ops->unthrottle(tty);
+		}
+	}
+	mutex_unlock(&tty->termios_mutex);
+
+	return ret;
+}
+
+/**
  *	tty_wait_until_sent	-	wait for I/O to finish
  *	@tty: tty we are waiting for
  *	@timeout: how long we will wait
@@ -415,34 +479,6 @@ void tty_encode_baud_rate(struct tty_struct *tty, speed_t ibaud, speed_t obaud)
 EXPORT_SYMBOL_GPL(tty_encode_baud_rate);
 
 /**
- *	tty_get_baud_rate	-	get tty bit rates
- *	@tty: tty to query
- *
- *	Returns the baud rate as an integer for this terminal. The
- *	termios lock must be held by the caller and the terminal bit
- *	flags may be updated.
- *
- *	Locking: none
- */
-
-speed_t tty_get_baud_rate(struct tty_struct *tty)
-{
-	speed_t baud = tty_termios_baud_rate(&tty->termios);
-
-	if (baud == 38400 && tty->alt_speed) {
-		if (!tty->warned) {
-			printk(KERN_WARNING "Use of setserial/setrocket to "
-					    "set SPD_* flags is deprecated\n");
-			tty->warned = 1;
-		}
-		baud = tty->alt_speed;
-	}
-
-	return baud;
-}
-EXPORT_SYMBOL(tty_get_baud_rate);
-
-/**
  *	tty_termios_copy_hw	-	copy hardware settings
  *	@new: New termios
  *	@old: Old termios
@@ -1086,14 +1122,12 @@ int tty_mode_ioctl(struct tty_struct *tty, struct file *file,
 }
 EXPORT_SYMBOL_GPL(tty_mode_ioctl);
 
-int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
+
+/* Caller guarantees ldisc reference is held */
+static int __tty_perform_flush(struct tty_struct *tty, unsigned long arg)
 {
-	struct tty_ldisc *ld;
-	int retval = tty_check_change(tty);
-	if (retval)
-		return retval;
+	struct tty_ldisc *ld = tty->ldisc;
 
-	ld = tty_ldisc_ref_wait(tty);
 	switch (arg) {
 	case TCIFLUSH:
 		if (ld && ld->ops->flush_buffer) {
@@ -1111,12 +1145,24 @@ int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
 		tty_driver_flush_buffer(tty);
 		break;
 	default:
-		tty_ldisc_deref(ld);
 		return -EINVAL;
 	}
-	tty_ldisc_deref(ld);
 	return 0;
 }
+
+int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
+{
+	struct tty_ldisc *ld;
+	int retval = tty_check_change(tty);
+	if (retval)
+		return retval;
+
+	ld = tty_ldisc_ref_wait(tty);
+	retval = __tty_perform_flush(tty, arg);
+	if (ld)
+		tty_ldisc_deref(ld);
+	return retval;
+}
 EXPORT_SYMBOL_GPL(tty_perform_flush);
 
 int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
@@ -1155,7 +1201,7 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
 		}
 		return 0;
 	case TCFLSH:
-		return tty_perform_flush(tty, arg);
+		return __tty_perform_flush(tty, arg);
 	default:
 		/* Try the mode commands */
 		return tty_mode_ioctl(tty, file, cmd, arg);