slip: not call free_netdev before rtnl_unlock in slip_open

BugLink: https://bugs.launchpad.net/bugs/1883918

commit f596c870 upstream.

As the description before netdev_run_todo, we cannot call free_netdev
before rtnl_unlock, fix it by reorder the code.
Signed-off-by: yangerkun <yangerkun@huawei.com>
Reviewed-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to <4.11: free_netdev() is called through sl_free_netdev()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/net/slip/slip.c

@@ -867,7 +867,10 @@ static int slip_open(struct tty_struct *tty)
 	sl->tty = NULL;
 	tty->disc_data = NULL;
 	clear_bit(SLF_INUSE, &sl->flags);
+	/* do not call free_netdev before rtnl_unlock */
+	rtnl_unlock();
 	sl_free_netdev(sl->dev);
+	return err;
 
 err_exit:
 	rtnl_unlock();