Revert "tty: pty: Fix race condition between release_one_tty and pty_write"

This reverts commit b9ca5f8560af244489b4a1bc1ae88b341f24bc95 as 0-day
shows it has a circular locking dependency.

Fixes: b9ca5f8560af ("tty: pty: Fix race condition between release_one_tty and pty_write")
Reported-by: kernel test robot <[e-mail]>
Cc: Sahara <[e-mail]>
Cc: stable <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/pty.c

···
 	if (tty->stopped)
 		return 0;
 
-	mutex_lock(&tty_mutex);
-	if (to->magic != TTY_MAGIC) {
-		mutex_unlock(&tty_mutex);
-		return -EIO;
-	}
-
 	if (c > 0) {
 		spin_lock_irqsave(&to->port->lock, flags);
 		/* Stuff the data into the input queue of the other end */
···
 			tty_flip_buffer_push(to->port);
 		spin_unlock_irqrestore(&to->port->lock, flags);
 	}
-	mutex_unlock(&tty_mutex);
 	return c;
 }
 

drivers/tty/tty_io.c

···
 	struct tty_driver *driver = tty->driver;
 	struct module *owner = driver->owner;
 
-	mutex_lock(&tty_mutex);
 	if (tty->ops->cleanup)
 		tty->ops->cleanup(tty);
 
 	tty->magic = 0;
-	mutex_unlock(&tty_mutex);
-
 	tty_driver_kref_put(driver);
 	module_put(owner);