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

This reverts commit b9ca5f85 as 0-day
shows it has a circular locking dependency.

Fixes: b9ca5f85 ("tty: pty: Fix race condition between release_one_tty and pty_write")
Reported-by: Nkernel test robot <lkp@intel.com>
Cc: Sahara <keun-o.park@darkmatter.ae>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -116,12 +116,6 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int 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 */
@@ -131,7 +125,6 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
 			tty_flip_buffer_push(to->port);
 		spin_unlock_irqrestore(&to->port->lock, flags);
 	}
-	mutex_unlock(&tty_mutex);
 	return c;
 }
 

drivers/tty/tty_io.c

@@ -1448,13 +1448,10 @@ static void release_one_tty(struct work_struct *work)
 	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);