bonding: add some slack to arp monitoring time limits

Currently, all the time limits in the bonding ARP monitor are in
multiples of arp_interval -- the time interval at which the ARP
monitor is periodically scheduled.

With a fast network round-trip and a little scheduling latency
of the ARP monitor work, a limit of n*delta_in_ticks may
effectively mean (n-1)*delta_in_ticks.

This is fatal in case of n==1  (the link will stay down
forever) and makes the behaviour non-deterministic in all the
other cases.

Add a delta_in_ticks/2 time slack to all the time limits.

Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 11 deletions

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index b24ce257ac7..7858c58df4a 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2811,12 +2811,13 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
                                             arp_work.work);
         struct slave *slave, *oldcurrent;
         int do_failover = 0;
-        int delta_in_ticks;
+        int delta_in_ticks, extra_ticks;
         int i;
 
         read_lock(&bond->lock);
 
         delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
+        extra_ticks = delta_in_ticks / 2;
 
         if (bond->slave_cnt == 0)
                 goto re_arm;
@@ -2839,10 +2840,10 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
                 if (slave->link != BOND_LINK_UP) {
                         if (time_in_range(jiffies,
                                 trans_start - delta_in_ticks,
-                                trans_start + delta_in_ticks) &&
+                                trans_start + delta_in_ticks + extra_ticks) &&
                             time_in_range(jiffies,
                                 slave->dev->last_rx - delta_in_ticks,
-                                slave->dev->last_rx + delta_in_ticks)) {
+                                slave->dev->last_rx + delta_in_ticks + extra_ticks)) {
 
                                 slave->link  = BOND_LINK_UP;
                                 bond_set_active_slave(slave);
@@ -2872,10 +2873,10 @@ void bond_loadbalance_arp_mon(struct work_struct *work)
                          */
                         if (!time_in_range(jiffies,
                                 trans_start - delta_in_ticks,
-                                trans_start + 2 * delta_in_ticks) ||
+                                trans_start + 2 * delta_in_ticks + extra_ticks) ||
                             !time_in_range(jiffies,
                                 slave->dev->last_rx - delta_in_ticks,
-                                slave->dev->last_rx + 2 * delta_in_ticks)) {
+                                slave->dev->last_rx + 2 * delta_in_ticks + extra_ticks)) {
 
                                 slave->link  = BOND_LINK_DOWN;
                                 bond_set_backup_slave(slave);
@@ -2933,6 +2934,14 @@ static int bond_ab_arp_inspect(struct bonding *bond, int delta_in_ticks)
         struct slave *slave;
         int i, commit = 0;
         unsigned long trans_start;
+        int extra_ticks;
+
+        /* All the time comparisons below need some extra time. Otherwise, on
+         * fast networks the ARP probe/reply may arrive within the same jiffy
+         * as it was sent.  Then, the next time the ARP monitor is run, one
+         * arp_interval will already have passed in the comparisons.
+         */
+        extra_ticks = delta_in_ticks / 2;
 
         bond_for_each_slave(bond, slave, i) {
                 slave->new_link = BOND_LINK_NOCHANGE;
@@ -2940,7 +2949,7 @@ static int bond_ab_arp_inspect(struct bonding *bond, int delta_in_ticks)
                 if (slave->link != BOND_LINK_UP) {
                         if (time_in_range(jiffies,
                                 slave_last_rx(bond, slave) - delta_in_ticks,
-                                slave_last_rx(bond, slave) + delta_in_ticks)) {
+                                slave_last_rx(bond, slave) + delta_in_ticks + extra_ticks)) {
 
                                 slave->new_link = BOND_LINK_UP;
                                 commit++;
@@ -2956,7 +2965,7 @@ static int bond_ab_arp_inspect(struct bonding *bond, int delta_in_ticks)
                  */
                 if (time_in_range(jiffies,
                                   slave->jiffies - delta_in_ticks,
-                                  slave->jiffies + 2 * delta_in_ticks))
+                                  slave->jiffies + 2 * delta_in_ticks + extra_ticks))
                         continue;
 
                 /*
@@ -2976,7 +2985,7 @@ static int bond_ab_arp_inspect(struct bonding *bond, int delta_in_ticks)
                     !bond->current_arp_slave &&
                     !time_in_range(jiffies,
                         slave_last_rx(bond, slave) - delta_in_ticks,
-                        slave_last_rx(bond, slave) + 3 * delta_in_ticks)) {
+                        slave_last_rx(bond, slave) + 3 * delta_in_ticks + extra_ticks)) {
 
                         slave->new_link = BOND_LINK_DOWN;
                         commit++;
@@ -2992,10 +3001,10 @@ static int bond_ab_arp_inspect(struct bonding *bond, int delta_in_ticks)
                 if (bond_is_active_slave(slave) &&
                     (!time_in_range(jiffies,
                         trans_start - delta_in_ticks,
-                        trans_start + 2 * delta_in_ticks) ||
+                        trans_start + 2 * delta_in_ticks + extra_ticks) ||
                      !time_in_range(jiffies,
                         slave_last_rx(bond, slave) - delta_in_ticks,
-                        slave_last_rx(bond, slave) + 2 * delta_in_ticks))) {
+                        slave_last_rx(bond, slave) + 2 * delta_in_ticks + extra_ticks))) {
 
                         slave->new_link = BOND_LINK_DOWN;
                         commit++;
@@ -3027,7 +3036,7 @@ static void bond_ab_arp_commit(struct bonding *bond, int delta_in_ticks)
                         if ((!bond->curr_active_slave &&
                              time_in_range(jiffies,
                                            trans_start - delta_in_ticks,
-                                           trans_start + delta_in_ticks)) ||
+                                           trans_start + delta_in_ticks + delta_in_ticks / 2)) ||
                             bond->curr_active_slave != slave) {
                                 slave->link = BOND_LINK_UP;
                                 if (bond->current_arp_slave) {