TTY: remove tty_locked

We used it really only serial and ami_serial. The rest of the
callsites were BUG/WARN_ONs to check if BTM is held. Now that we
pruned tty_locked from both of the real users, we can get rid of
tty_lock along with __big_tty_mutex_owner.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/tty/serial/serial_core.c

@@ -1245,8 +1245,6 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
 	struct uart_port *uport;
 	unsigned long flags;
 
-	BUG_ON(!tty_locked());
-
 	if (!state)
 		return;
 
@@ -1411,7 +1409,6 @@ static void uart_hangup(struct tty_struct *tty)
 	struct tty_port *port = &state->port;
 	unsigned long flags;
 
-	BUG_ON(!tty_locked());
 	pr_debug("uart_hangup(%d)\n", state->uart_port->line);
 
 	mutex_lock(&port->mutex);
@@ -1498,7 +1495,6 @@ static int uart_open(struct tty_struct *tty, struct file *filp)
 	struct tty_port *port;
 	int retval, line = tty->index;
 
-	BUG_ON(!tty_locked());
 	pr_debug("uart_open(%d) called\n", line);
 
 	/*

drivers/tty/tty_ldisc.c

@@ -450,7 +450,6 @@ static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 	if (ld->ops->open) {
 		int ret;
                 /* BTM here locks versus a hangup event */
-		WARN_ON(!tty_locked());
 		ret = ld->ops->open(tty);
 		if (ret)
 			clear_bit(TTY_LDISC_OPEN, &tty->flags);

drivers/tty/tty_mutex.c

@@ -15,30 +15,18 @@
  * Don't use in new code.
  */
 static DEFINE_MUTEX(big_tty_mutex);
-struct task_struct *__big_tty_mutex_owner;
-EXPORT_SYMBOL_GPL(__big_tty_mutex_owner);
 
 /*
  * Getting the big tty mutex.
  */
 void __lockfunc tty_lock(void)
 {
-	struct task_struct *task = current;
-
-	WARN_ON(__big_tty_mutex_owner == task);
-
 	mutex_lock(&big_tty_mutex);
-	__big_tty_mutex_owner = task;
 }
 EXPORT_SYMBOL(tty_lock);
 
 void __lockfunc tty_unlock(void)
 {
-	struct task_struct *task = current;
-
-	WARN_ON(__big_tty_mutex_owner != task);
-	__big_tty_mutex_owner = NULL;
-
 	mutex_unlock(&big_tty_mutex);
 }
 EXPORT_SYMBOL(tty_unlock);

drivers/tty/vt/selection.c

@@ -301,6 +301,8 @@ int set_selection(const struct tiocl_selection __user *sel, struct tty_struct *t
 /* Insert the contents of the selection buffer into the
  * queue of the tty associated with the current console.
  * Invoked by ioctl().
+ *
+ * Locking: always called with BTM from vt_ioctl
  */
 int paste_selection(struct tty_struct *tty)
 {
@@ -310,8 +312,6 @@ int paste_selection(struct tty_struct *tty)
 	struct  tty_ldisc *ld;
 	DECLARE_WAITQUEUE(wait, current);
 
-	/* always called with BTM from vt_ioctl */
-	WARN_ON(!tty_locked());
 
 	console_lock();
 	poke_blanked_console();

include/linux/tty.h

@@ -600,8 +600,6 @@ extern long vt_compat_ioctl(struct tty_struct *tty,
 /* functions for preparation of BKL removal */
 extern void __lockfunc tty_lock(void) __acquires(tty_lock);
 extern void __lockfunc tty_unlock(void) __releases(tty_lock);
-extern struct task_struct *__big_tty_mutex_owner;
-#define tty_locked()		(current == __big_tty_mutex_owner)
 
 /*
  * wait_event_interruptible_tty -- wait for a condition with the tty lock held