bonding: rebuild the lock use for bond_activebackup_arp_mon()

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 to replace with the bond lock, to the bond slave
list need to called in RCU, add a new bond_first_slave_rcu()
to get the first slave in RCU protection.

In bond_ab_arp_probe(), the bond->current_arp_slave may changd
if bond release slave, just like:

        bond_ab_arp_probe()                     bond_release()
        cpu 0                                   cpu 1
        ...
        if (bond->current_arp_slave...)         ...
        ...                             bond->current_arp_slave = NULl
        bond->current_arp_slave->dev->name      ...

So the current_arp_slave need to dereference in the section.

Suggested-by: Nikolay Aleksandrov <nikolay@redhat.com>
Suggested-by: Jay Vosburgh <fubar@us.ibm.com>
Suggested-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 25 deletions

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 1781ea620d76..bad1bf949546 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2517,7 +2517,7 @@ re_arm:
  * place for the slave.  Returns 0 if no changes are found, >0 if changes
  * to link states must be committed.
  *
- * Called with bond->lock held for read.
+ * Called with rcu_read_lock hold.
  */
 static int bond_ab_arp_inspect(struct bonding *bond)
 {
@@ -2526,7 +2526,7 @@ 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);
 
@@ -2588,7 +2588,7 @@ 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)
 {
@@ -2663,19 +2663,20 @@ 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)
 {
-        struct slave *slave, *before = NULL, *new_slave = NULL;
+        struct slave *slave, *before = NULL, *new_slave = NULL,
+                     *curr_arp_slave = rcu_dereference(bond->current_arp_slave);
         struct list_head *iter;
         bool found = false;
 
         read_lock(&bond->curr_slave_lock);
 
-        if (bond->current_arp_slave && bond->curr_active_slave)
+        if (curr_arp_slave && bond->curr_active_slave)
                 pr_info("PROBE: c_arp %s && cas %s BAD\n",
-                        bond->current_arp_slave->dev->name,
+                        curr_arp_slave->dev->name,
                         bond->curr_active_slave->dev->name);
 
         if (bond->curr_active_slave) {
@@ -2691,15 +2692,15 @@ static void bond_ab_arp_probe(struct bonding *bond)
          * for becoming the curr_active_slave
          */
 
-        if (!bond->current_arp_slave) {
-                bond->current_arp_slave = bond_first_slave(bond);
-                if (!bond->current_arp_slave)
+        if (!curr_arp_slave) {
+                curr_arp_slave = bond_first_slave_rcu(bond);
+                if (!curr_arp_slave)
                         return;
         }
 
-        bond_set_slave_inactive_flags(bond->current_arp_slave);
+        bond_set_slave_inactive_flags(curr_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;
 
@@ -2722,7 +2723,7 @@ static void bond_ab_arp_probe(struct bonding *bond)
                         pr_info("%s: backup interface %s is now down.\n",
                                 bond->dev->name, slave->dev->name);
                 }
-                if (slave == bond->current_arp_slave)
+                if (slave == curr_arp_slave)
                         found = true;
         }
 
@@ -2736,8 +2737,7 @@ static void bond_ab_arp_probe(struct bonding *bond)
         bond_set_slave_active_flags(new_slave);
         bond_arp_send_all(bond, new_slave);
         new_slave->jiffies = jiffies;
-        bond->current_arp_slave = new_slave;
-
+        rcu_assign_pointer(bond->current_arp_slave, new_slave);
 }
 
 void bond_activebackup_arp_mon(struct work_struct *work)
@@ -2747,43 +2747,38 @@ 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))
                 goto re_arm;
 
+        rcu_read_lock();
+
         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);
                 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;