tty: release BTM while sleeping in block_til_ready

Most tty drivers may block while opening a device.
Since this possibly depends on another thread
closing it first and both threads may need the BTM,
we need to release it here.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/ip2/ip2main.c b/drivers/char/ip2/ip2main.c
index 911e1da..07f3ea3 100644
--- a/drivers/char/ip2/ip2main.c
+++ b/drivers/char/ip2/ip2main.c
@@ -1486,7 +1486,9 @@
 
 	if ( tty_hung_up_p(pFile) || ( pCh->flags & ASYNC_CLOSING )) {
 		if ( pCh->flags & ASYNC_CLOSING ) {
+			tty_unlock();
 			schedule();
+			tty_lock();
 		}
 		if ( tty_hung_up_p(pFile) ) {
 			set_current_state( TASK_RUNNING );
@@ -1548,7 +1550,9 @@
 			rc = (( pCh->flags & ASYNC_HUP_NOTIFY ) ? -EAGAIN : -ERESTARTSYS);
 			break;
 		}
+		tty_unlock();
 		schedule();
+		tty_lock();
 	}
 	set_current_state( TASK_RUNNING );
 	remove_wait_queue(&pCh->open_wait, &wait);