tty: Revert the tty locking series, it needs more work

This reverts the tty layer change to use per-tty locking, because it's
not correct yet, and fixing it will require some more deep surgery.

The main revert is d29f3ef39b ("tty_lock: Localise the lock"), but
there are several smaller commits that built upon it, they also get
reverted here. The list of reverted commits is:

  fde86d3108 - tty: add lockdep annotations
  8f6576ad47 - tty: fix ldisc lock inversion trace
  d3ca8b64b9 - pty: Fix lock inversion
  b1d679afd7 - tty: drop the pty lock during hangup
  abcefe5fc3 - tty/amiserial: Add missing argument for tty_unlock()
  fd11b42e35 - cris: fix missing tty arg in wait_event_interruptible_tty call
  d29f3ef39b - tty_lock: Localise the lock

The revert had a trivial conflict in the 68360serial.c staging driver
that got removed in the meantime.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/tty/tty_mutex.c

@@ -4,70 +4,29 @@
 #include <linux/semaphore.h>
 #include <linux/sched.h>
 
-/* Legacy tty mutex glue */
-
-enum {
-	TTY_MUTEX_NORMAL,
-	TTY_MUTEX_NESTED,
-};
+/*
+ * The 'big tty mutex'
+ *
+ * This mutex is taken and released by tty_lock() and tty_unlock(),
+ * replacing the older big kernel lock.
+ * It can no longer be taken recursively, and does not get
+ * released implicitly while sleeping.
+ *
+ * Don't use in new code.
+ */
+static DEFINE_MUTEX(big_tty_mutex);
 
 /*
  * Getting the big tty mutex.
  */
-
-static void __lockfunc tty_lock_nested(struct tty_struct *tty,
-				       unsigned int subclass)
+void __lockfunc tty_lock(void)
 {
-	if (tty->magic != TTY_MAGIC) {
-		printk(KERN_ERR "L Bad %p\n", tty);
-		WARN_ON(1);
-		return;
-	}
-	tty_kref_get(tty);
-	mutex_lock_nested(&tty->legacy_mutex, subclass);
-}
-
-void __lockfunc tty_lock(struct tty_struct *tty)
-{
-	return tty_lock_nested(tty, TTY_MUTEX_NORMAL);
+	mutex_lock(&big_tty_mutex);
 }
 EXPORT_SYMBOL(tty_lock);
 
-void __lockfunc tty_unlock(struct tty_struct *tty)
+void __lockfunc tty_unlock(void)
 {
-	if (tty->magic != TTY_MAGIC) {
-		printk(KERN_ERR "U Bad %p\n", tty);
-		WARN_ON(1);
-		return;
-	}
-	mutex_unlock(&tty->legacy_mutex);
-	tty_kref_put(tty);
+	mutex_unlock(&big_tty_mutex);
 }
 EXPORT_SYMBOL(tty_unlock);
-
-/*
- * Getting the big tty mutex for a pair of ttys with lock ordering
- * On a non pty/tty pair tty2 can be NULL which is just fine.
- */
-void __lockfunc tty_lock_pair(struct tty_struct *tty,
-					struct tty_struct *tty2)
-{
-	if (tty < tty2) {
-		tty_lock(tty);
-		tty_lock_nested(tty2, TTY_MUTEX_NESTED);
-	} else {
-		if (tty2 && tty2 != tty)
-			tty_lock(tty2);
-		tty_lock_nested(tty, TTY_MUTEX_NESTED);
-	}
-}
-EXPORT_SYMBOL(tty_lock_pair);
-
-void __lockfunc tty_unlock_pair(struct tty_struct *tty,
-						struct tty_struct *tty2)
-{
-	tty_unlock(tty);
-	if (tty2 && tty2 != tty)
-		tty_unlock(tty2);
-}
-EXPORT_SYMBOL(tty_unlock_pair);