Use guards in the pty code. This improves readability, makes error
handling easier, and marks locked portions of code explicit. All that
while being sure the lock is unlocked.

pty_set_pktmode() is handled specially -- the conditions are inverted
and return called if conditions unmet. This avoid double nested 'if's.
The variable is renamed to want_pktmode so it is not confused with the
current state of pktmode.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
---
 drivers/tty/pty.c | 103 ++++++++++++++++++++--------------------------
 1 file changed, 45 insertions(+), 58 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 8bb1a01fef2a..76188b8f3ba3 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -57,9 +57,8 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	set_bit(TTY_IO_ERROR, &tty->flags);
 	wake_up_interruptible(&tty->read_wait);
 	wake_up_interruptible(&tty->write_wait);
-	spin_lock_irq(&tty->ctrl.lock);
-	tty->ctrl.packet = false;
-	spin_unlock_irq(&tty->ctrl.lock);
+	scoped_guard(spinlock_irq, &tty->ctrl.lock)
+		tty->ctrl.packet = false;
 	/* Review - krefs on tty_link ?? */
 	if (!tty->link)
 		return;
@@ -70,10 +69,9 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 		set_bit(TTY_OTHER_CLOSED, &tty->flags);
 #ifdef CONFIG_UNIX98_PTYS
 		if (tty->driver == ptm_driver) {
-			mutex_lock(&devpts_mutex);
+			guard(mutex)(&devpts_mutex);
 			if (tty->link->driver_data)
 				devpts_pty_kill(tty->link->driver_data);
-			mutex_unlock(&devpts_mutex);
 		}
 #endif
 		tty_vhangup(tty->link);
@@ -157,21 +155,23 @@ static int pty_get_lock(struct tty_struct *tty, int __user *arg)
 /* Set the packet mode on a pty */
 static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
 {
-	int pktmode;
+	int want_pktmode;
 
-	if (get_user(pktmode, arg))
+	if (get_user(want_pktmode, arg))
 		return -EFAULT;
 
-	spin_lock_irq(&tty->ctrl.lock);
-	if (pktmode) {
-		if (!tty->ctrl.packet) {
-			tty->link->ctrl.pktstatus = 0;
-			smp_mb();
-			tty->ctrl.packet = true;
-		}
-	} else
+	guard(spinlock_irq)(&tty->ctrl.lock);
+	if (!want_pktmode) {
 		tty->ctrl.packet = false;
-	spin_unlock_irq(&tty->ctrl.lock);
+		return 0;
+	}
+
+	if (tty->ctrl.packet)
+		return 0;
+
+	tty->link->ctrl.pktstatus = 0;
+	smp_mb();
+	tty->ctrl.packet = true;
 
 	return 0;
 }
@@ -210,10 +210,9 @@ static void pty_flush_buffer(struct tty_struct *tty)
 
 	tty_buffer_flush(to, NULL);
 	if (to->ctrl.packet) {
-		spin_lock_irq(&tty->ctrl.lock);
+		guard(spinlock_irq)(&tty->ctrl.lock);
 		tty->ctrl.pktstatus |= TIOCPKT_FLUSHWRITE;
 		wake_up_interruptible(&to->read_wait);
-		spin_unlock_irq(&tty->ctrl.lock);
 	}
 }
 
@@ -252,17 +251,17 @@ static void pty_set_termios(struct tty_struct *tty,
 				STOP_CHAR(tty) == '\023' &&
 				START_CHAR(tty) == '\021');
 		if ((old_flow != new_flow) || extproc) {
-			spin_lock_irq(&tty->ctrl.lock);
-			if (old_flow != new_flow) {
-				tty->ctrl.pktstatus &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
-				if (new_flow)
-					tty->ctrl.pktstatus |= TIOCPKT_DOSTOP;
-				else
-					tty->ctrl.pktstatus |= TIOCPKT_NOSTOP;
+			scoped_guard(spinlock_irq, &tty->ctrl.lock) {
+				if (old_flow != new_flow) {
+					tty->ctrl.pktstatus &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
+					if (new_flow)
+						tty->ctrl.pktstatus |= TIOCPKT_DOSTOP;
+					else
+						tty->ctrl.pktstatus |= TIOCPKT_NOSTOP;
+				}
+				if (extproc)
+					tty->ctrl.pktstatus |= TIOCPKT_IOCTL;
 			}
-			if (extproc)
-				tty->ctrl.pktstatus |= TIOCPKT_IOCTL;
-			spin_unlock_irq(&tty->ctrl.lock);
 			wake_up_interruptible(&tty->link->read_wait);
 		}
 	}
@@ -286,9 +285,9 @@ static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
 	struct tty_struct *pty = tty->link;
 
 	/* For a PTY we need to lock the tty side */
-	mutex_lock(&tty->winsize_mutex);
+	guard(mutex)(&tty->winsize_mutex);
 	if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
-		goto done;
+		return 0;
 
 	/* Signal the foreground process group of both ptys */
 	pgrp = tty_get_pgrp(tty);
@@ -304,8 +303,7 @@ static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
 
 	tty->winsize = *ws;
 	pty->winsize = *ws;	/* Never used so will go away soon */
-done:
-	mutex_unlock(&tty->winsize_mutex);
+
 	return 0;
 }
 
@@ -321,28 +319,26 @@ static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
  */
 static void pty_start(struct tty_struct *tty)
 {
-	unsigned long flags;
+	if (!tty->link || !tty->link->ctrl.packet)
+		return;
 
-	if (tty->link && tty->link->ctrl.packet) {
-		spin_lock_irqsave(&tty->ctrl.lock, flags);
+	scoped_guard(spinlock_irqsave, &tty->ctrl.lock) {
 		tty->ctrl.pktstatus &= ~TIOCPKT_STOP;
 		tty->ctrl.pktstatus |= TIOCPKT_START;
-		spin_unlock_irqrestore(&tty->ctrl.lock, flags);
-		wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
 	}
+	wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
 }
 
 static void pty_stop(struct tty_struct *tty)
 {
-	unsigned long flags;
+	if (!tty->link || !tty->link->ctrl.packet)
+		return;
 
-	if (tty->link && tty->link->ctrl.packet) {
-		spin_lock_irqsave(&tty->ctrl.lock, flags);
+	scoped_guard(spinlock_irqsave, &tty->ctrl.lock) {
 		tty->ctrl.pktstatus &= ~TIOCPKT_START;
 		tty->ctrl.pktstatus |= TIOCPKT_STOP;
-		spin_unlock_irqrestore(&tty->ctrl.lock, flags);
-		wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
 	}
+	wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
 }
 
 /**
@@ -705,15 +701,9 @@ static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
 static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
 		struct file *file, int idx)
 {
-	struct tty_struct *tty;
-
-	mutex_lock(&devpts_mutex);
-	tty = devpts_get_priv(file->f_path.dentry);
-	mutex_unlock(&devpts_mutex);
+	guard(mutex)(&devpts_mutex);
 	/* Master must be open before slave */
-	if (!tty)
-		return ERR_PTR(-EIO);
-	return tty;
+	return devpts_get_priv(file->f_path.dentry) ? : ERR_PTR(-EIO);
 }
 
 static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
@@ -811,20 +801,17 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 	}
 
 	/* find a device that is not in use. */
-	mutex_lock(&devpts_mutex);
-	index = devpts_new_index(fsi);
-	mutex_unlock(&devpts_mutex);
+	scoped_guard(mutex, &devpts_mutex)
+		index = devpts_new_index(fsi);
 
 	retval = index;
 	if (index < 0)
 		goto out_put_fsi;
 
 
-	mutex_lock(&tty_mutex);
-	tty = tty_init_dev(ptm_driver, index);
-	/* The tty returned here is locked so we can safely
-	   drop the mutex */
-	mutex_unlock(&tty_mutex);
+	/* The tty returned here is locked so we can safely drop the mutex */
+	scoped_guard(mutex, &tty_mutex)
+		tty = tty_init_dev(ptm_driver, index);
 
 	retval = PTR_ERR(tty);
 	if (IS_ERR(tty))
-- 
2.51.1