[PATCH net-next v2 6/10] bonding: rebuild the lock use for bond_activebackup_arp_mon()

[Ding Tianhong <dingtianhong@huawei.com>]

The bond_activebackup_arp_mon() use the bond lock for read to
protect the slave list, it is no effect, and the RTNL is only
called for bond_ab_arp_commit() and peer notify, for the performance
better, use RCU instead of the bond lock, because the bond slave
list need to called in RCU, add a new bond_first_slave_rcu()
to get the first slave in RCU protection.

When bond_ab_arp_inspect() and should_notify_peers is true, the
RTNL will called twice, it is a loss of performance, so make the
two RTNL together to avoid performance loss.

Suggested-by: Jay Vosburgh <fubar@us.ibm.com>
Suggested-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
---
 drivers/net/bonding/bond_main.c | 35 +++++++++++++++++++----------------
 drivers/net/bonding/bonding.h   |  7 +++++++
 2 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 759dcd0..b48ca55 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2524,7 +2524,7 @@ static int bond_ab_arp_inspect(struct bonding *bond)
 	struct slave *slave;
 	int commit = 0;
 
-	bond_for_each_slave(bond, slave, iter) {
+	bond_for_each_slave_rcu(bond, slave, iter) {
 		slave->new_link = BOND_LINK_NOCHANGE;
 		last_rx = slave_last_rx(bond, slave);
 
@@ -2586,7 +2586,7 @@ static int bond_ab_arp_inspect(struct bonding *bond)
  * Called to commit link state changes noted by inspection step of
  * active-backup mode ARP monitor.
  *
- * Called with RTNL and bond->lock for read.
+ * Called with RTNL hold.
  */
 static void bond_ab_arp_commit(struct bonding *bond)
 {
@@ -2661,7 +2661,7 @@ do_failover:
 /*
  * Send ARP probes for active-backup mode ARP monitor.
  *
- * Called with bond->lock held for read.
+ * Called with rcu_read_lock hold.
  */
 static void bond_ab_arp_probe(struct bonding *bond)
 {
@@ -2690,14 +2690,14 @@ static void bond_ab_arp_probe(struct bonding *bond)
 	 */
 
 	if (!bond->current_arp_slave) {
-		bond->current_arp_slave = bond_first_slave(bond);
+		bond->current_arp_slave = bond_first_slave_rcu(bond);
 		if (!bond->current_arp_slave)
 			return;
 	}
 
 	bond_set_slave_inactive_flags(bond->current_arp_slave);
 
-	bond_for_each_slave(bond, slave, iter) {
+	bond_for_each_slave_rcu(bond, slave, iter) {
 		if (!found && !before && IS_UP(slave->dev))
 			before = slave;
 
@@ -2745,43 +2745,46 @@ void bond_activebackup_arp_mon(struct work_struct *work)
 	bool should_notify_peers = false;
 	int delta_in_ticks;
 
-	read_lock(&bond->lock);
-
 	delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
 
-	if (!bond_has_slaves(bond))
+	rcu_read_lock();
+
+	if (!bond_has_slaves_rcu(bond)) {
+		rcu_read_unlock();
 		goto re_arm;
+	}
 
 	should_notify_peers = bond_should_notify_peers(bond);
 
 	if (bond_ab_arp_inspect(bond)) {
-		read_unlock(&bond->lock);
+		rcu_read_unlock();
 
 		/* Race avoidance with bond_close flush of workqueue */
 		if (!rtnl_trylock()) {
-			read_lock(&bond->lock);
 			delta_in_ticks = 1;
 			should_notify_peers = false;
 			goto re_arm;
 		}
 
-		read_lock(&bond->lock);
-
 		bond_ab_arp_commit(bond);
 
-		read_unlock(&bond->lock);
+		if (should_notify_peers) {
+			call_netdevice_notifiers(NETDEV_NOTIFY_PEERS,
+					bond->dev);
+			should_notify_peers = false;
+		}
+
 		rtnl_unlock();
-		read_lock(&bond->lock);
+		rcu_read_lock();
 	}
 
 	bond_ab_arp_probe(bond);
+	rcu_read_unlock();
 
 re_arm:
 	if (bond->params.arp_interval)
 		queue_delayed_work(bond->wq, &bond->arp_work, delta_in_ticks);
 
-	read_unlock(&bond->lock);
-
 	if (should_notify_peers) {
 		if (!rtnl_trylock())
 			return;
diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
index deb9738..90b745c 100644
--- a/drivers/net/bonding/bonding.h
+++ b/drivers/net/bonding/bonding.h
@@ -97,6 +97,13 @@
 		netdev_adjacent_get_private(bond_slave_list(bond)->prev) : \
 		NULL)
 
+#define bond_first_slave_rcu(bond) \
+	({struct list_head *__ptr = (bond_slave_list(bond)); \
+	 struct list_head *__next = ACCESS_ONCE(__ptr->next); \
+	 likely(__ptr != __next) ? \
+	 netdev_adjacent_get_private_rcu(__next) : NULL; \
+	 })
+
 #define bond_is_first_slave(bond, pos) (pos == bond_first_slave(bond))
 #define bond_is_last_slave(bond, pos) (pos == bond_last_slave(bond))
 
-- 
1.8.2.1