tcm_fc: Resolve suspicious RCU usage warnings

commit 863555b upstream.

Use rcu_dereference_protected to tell rcu that the ft_lport_lock
is held during ft_lport_create. This resolved "suspicious RCU usage"
warnings when debugging options are turned on.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/target/tcm_fc/tfc_sess.c

@@ -61,7 +61,8 @@ static struct ft_tport *ft_tport_create(struct fc_lport *lport)
 	struct ft_tport *tport;
 	int i;
 
-	tport = rcu_dereference(lport->prov[FC_TYPE_FCP]);
+	tport = rcu_dereference_protected(lport->prov[FC_TYPE_FCP],
+					  lockdep_is_held(&ft_lport_lock));
 	if (tport && tport->tpg)
 		return tport;