Staging: speakup: Update __speakup_paste_selection() tty (ab)usage to match vt

This function is largely a duplicate of paste_selection() in
drivers/tty/vt/selection.c, but with its own selection state.  The
speakup selection mechanism should really be merged with vt.

For now, apply the changes from 'TTY: vt, fix paste_selection ldisc
handling', 'tty: Make ldisc input flow control concurrency-friendly',
and 'tty: Fix unsafe vt paste_selection()'.

References: https://bugs.debian.org/735202
References: https://bugs.debian.org/744015
Reported-by: Paul Gevers <elbrus@debian.org>
Reported-and-tested-by: Jarek Czekalski <jarekczek@poczta.onet.pl>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: <stable@vger.kernel.org> # v3.8 but needs backporting for < 3.12
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index cf78d19..143deb6 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -60,6 +60,7 @@
 	atomic_inc(&buf->priority);
 	mutex_lock(&buf->lock);
 }
+EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
 
 void tty_buffer_unlock_exclusive(struct tty_port *port)
 {
@@ -73,6 +74,7 @@
 	if (restart)
 		queue_work(system_unbound_wq, &buf->work);
 }
+EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
 
 /**
  *	tty_buffer_space_avail	-	return unused buffer space