[PATCH] tty: remove useless memory barrier

I don't see why there is a memory barrier in copy_from_read_buf() at all.
Even if it was useful spin_unlock_irqrestore implies a barrier.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/char/n_tty.c

@@ -1151,7 +1151,6 @@ static int copy_from_read_buf(struct tty_struct *tty,
 	n = min(*nr, n);
 	spin_unlock_irqrestore(&tty->read_lock, flags);
 	if (n) {
-		mb();
 		retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
 		n -= retval;
 		spin_lock_irqsave(&tty->read_lock, flags);