bonding: Convert balance-rr transmit to new locking

Change locking in balance-rr transmit processing to use a free
running counter to determine which slave to transmit on. Instead, a
free-running counter is maintained, and modulo arithmetic used to select
a slave for transmit.

This removes lock operations from the TX path, and eliminates
a deadlock introduced by the conversion to work queues.

Signed-off-by: Andy Gospodarek <[e-mail]>
Signed-off-by: Jay Vosburgh <[e-mail]>
Signed-off-by: Jeff Garzik <[e-mail]>

drivers/net/bonding/bond_main.c

···
 {
 	struct bonding *bond = bond_dev->priv;
 	struct slave *slave, *start_at;
-	int i;
-	int res = 1;
+	int i, slave_no, res = 1;
 
 	read_lock(&bond->lock);
 
···
 		goto out;
 	}
 
-	read_lock(&bond->curr_slave_lock);
-	slave = start_at = bond->curr_active_slave;
-	read_unlock(&bond->curr_slave_lock);
+	/*
+	 * Concurrent TX may collide on rr_tx_counter; we accept that
+	 * as being rare enough not to justify using an atomic op here
+	 */
+	slave_no = bond->rr_tx_counter++ % bond->slave_cnt;
 
-	if (!slave) {
-		goto out;
+	bond_for_each_slave(bond, slave, i) {
+		slave_no--;
+		if (slave_no < 0) {
+			break;
+		}
 	}
 
+	start_at = slave;
 	bond_for_each_slave_from(bond, slave, i, start_at) {
 		if (IS_UP(slave->dev) &&
 		    (slave->link == BOND_LINK_UP) &&
 		    (slave->state == BOND_STATE_ACTIVE)) {
 			res = bond_dev_queue_xmit(bond, skb, slave->dev);
-
-			write_lock(&bond->curr_slave_lock);
-			bond->curr_active_slave = slave->next;
-			write_unlock(&bond->curr_slave_lock);
-
 			break;
 		}
 	}
-
 
 out:
 	if (res) {

drivers/net/bonding/bonding.h

···
 	int      (*xmit_hash_policy)(struct sk_buff *, struct net_device *, int);
 	__be32   master_ip;
 	u16      flags;
+	u16      rr_tx_counter;
 	struct   ad_bond_info ad_info;
 	struct   alb_bond_info alb_info;
 	struct   bond_params params;