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>

1 files changed, 36 insertions, 21 deletions

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 27e6fddb2206..dd75615d85f2 100644
--- 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)