bonding: RCUify bond_ab_arp_probe

Currently bond_ab_arp_probe() is always called under rcu_read_lock(),
however to work with curr_active_slave we're still holding the
curr_slave_lock.

To remove that curr_slave_lock - rcu_dereference the bond's
curr_active_slave and use it further - so that we're sure the slave won't
go away, and we don't care if it will change in the meanwhile.

CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -2605,25 +2605,21 @@ do_failover:
 static void bond_ab_arp_probe(struct bonding *bond)
 {
 	struct slave *slave, *before = NULL, *new_slave = NULL,
-		     *curr_arp_slave = rcu_dereference(bond->current_arp_slave);
+		     *curr_arp_slave = rcu_dereference(bond->current_arp_slave),
+		     *curr_active_slave = rcu_dereference(bond->curr_active_slave);
 	struct list_head *iter;
 	bool found = false;
 
-	read_lock(&bond->curr_slave_lock);
-
-	if (curr_arp_slave && bond->curr_active_slave)
+	if (curr_arp_slave && curr_active_slave)
 		pr_info("PROBE: c_arp %s && cas %s BAD\n",
 			curr_arp_slave->dev->name,
-			bond->curr_active_slave->dev->name);
+			curr_active_slave->dev->name);
 
-	if (bond->curr_active_slave) {
-		bond_arp_send_all(bond, bond->curr_active_slave);
-		read_unlock(&bond->curr_slave_lock);
+	if (curr_active_slave) {
+		bond_arp_send_all(bond, curr_active_slave);
 		return;
 	}
 
-	read_unlock(&bond->curr_slave_lock);
-
 	/* if we don't have a curr_active_slave, search for the next available
 	 * backup slave from the current_arp_slave and make it the candidate
 	 * for becoming the curr_active_slave