bonding: restructure locking of bond_ab_arp_probe()

Currently we're calling it from under RCU context, however we're using some
functions that require rtnl to be held.

Fix this by restructuring the locking - don't call it under any locks,
aquire rcu_read_lock() if we're sending _only_ (i.e. we have the active
slave present), and use rtnl locking otherwise - if we need to modify
(in)active flags of a slave.

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>

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 27e6fdd..dd75615 100644 (file)
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2599,17 +2599,18 @@ do_failover:
 
 /*
  * Send ARP probes for active-backup mode ARP monitor.
- *
- * Called with rcu_read_lock hold.
  */
-static void bond_ab_arp_probe(struct bonding *bond)
+static bool 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_active_slave = rcu_dereference(bond->curr_active_slave);
+                    *curr_arp_slave, *curr_active_slave;
        struct list_head *iter;
        bool found = false;
 
+       rcu_read_lock();
+       curr_arp_slave = rcu_dereference(bond->current_arp_slave);
+       curr_active_slave = rcu_dereference(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,
@@ -2617,23 +2618,32 @@ static void bond_ab_arp_probe(struct bonding *bond)
 
        if (curr_active_slave) {
                bond_arp_send_all(bond, curr_active_slave);
-               return;
+               rcu_read_unlock();
+               return true;
        }
+       rcu_read_unlock();
 
        /* 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
         */
 
+       if (!rtnl_trylock())
+               return false;
+       /* curr_arp_slave might have gone away */
+       curr_arp_slave = ACCESS_ONCE(bond->current_arp_slave);
+
        if (!curr_arp_slave) {
-               curr_arp_slave = bond_first_slave_rcu(bond);
-               if (!curr_arp_slave)
-                       return;
+               curr_arp_slave = bond_first_slave(bond);
+               if (!curr_arp_slave) {
+                       rtnl_unlock();
+                       return true;
+               }
        }
 
        bond_set_slave_inactive_flags(curr_arp_slave);
 
-       bond_for_each_slave_rcu(bond, slave, iter) {
+       bond_for_each_slave(bond, slave, iter) {
                if (!found && !before && IS_UP(slave->dev))
                        before = slave;
 
@@ -2663,21 +2673,26 @@ static void bond_ab_arp_probe(struct bonding *bond)
        if (!new_slave && before)
                new_slave = before;
 
-       if (!new_slave)
-               return;
+       if (!new_slave) {
+               rtnl_unlock();
+               return true;
+       }
 
        new_slave->link = BOND_LINK_BACK;
        bond_set_slave_active_flags(new_slave);
        bond_arp_send_all(bond, new_slave);
        new_slave->jiffies = jiffies;
        rcu_assign_pointer(bond->current_arp_slave, new_slave);
+       rtnl_unlock();
+
+       return true;
 }
 
 static void bond_activebackup_arp_mon(struct work_struct *work)
 {
        struct bonding *bond = container_of(work, struct bonding,
                                            arp_work.work);
-       bool should_notify_peers = false;
+       bool should_notify_peers = false, should_commit = false;
        int delta_in_ticks;
 
        delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
@@ -2686,12 +2701,11 @@ static void bond_activebackup_arp_mon(struct work_struct *work)
                goto re_arm;
 
        rcu_read_lock();
-
        should_notify_peers = bond_should_notify_peers(bond);
+       should_commit = bond_ab_arp_inspect(bond);
+       rcu_read_unlock();
 
-       if (bond_ab_arp_inspect(bond)) {
-               rcu_read_unlock();
-
+       if (should_commit) {
                /* Race avoidance with bond_close flush of workqueue */
                if (!rtnl_trylock()) {
                        delta_in_ticks = 1;
@@ -2700,13 +2714,14 @@ static void bond_activebackup_arp_mon(struct work_struct *work)
                }
 
                bond_ab_arp_commit(bond);
-
                rtnl_unlock();
-               rcu_read_lock();
        }
 
-       bond_ab_arp_probe(bond);
-       rcu_read_unlock();
+       if (!bond_ab_arp_probe(bond)) {
+               /* rtnl locking failed, re-arm */
+               delta_in_ticks = 1;
+               should_notify_peers = false;
+       }
 
 re_arm:
        if (bond->params.arp_interval)