[PATCH v4] net/bonding: send arp in interval if no active slave

[Jarod Wilson <jarod@redhat.com>]

From: Uwe Koziolek <uwe.koziolek@redknee.com>

With some very finicky switch hardware, active backup bonding can get into
a situation where we play ping-pong between interfaces, trying to get one
to come up as the active slave. There seems to be an issue with the
switch's arp replies either taking too long, or simply getting lost, so we
wind up unable to get any interface up and active. Sometimes, the issue
sorts itself out after a while, sometimes it doesn't.

Testing with num_grat_arp has proven fruitless, but sending an additional
arp on curr_arp_slave if we're still in the arp_interval timeslice in
bond_ab_arp_probe(), has shown to produce 100% reliability in testing with
this hardware combination.

[jarod: manufacturing of changelog, addition of modparam gating]
CC: Jay Vosburgh <jay.vosburgh@canonical.com>
CC: Andy Gospodarek <gospo@cumulusnetworks.com>
CC: Veaceslav Falico <vfalico@gmail.com>
CC: netdev@vger.kernel.org
Signed-off-by: Uwe Koziolek <uwe.koziolek@redknee.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
---
v2: add code comment as to why change is needed
v3: fix wrapping of comments
v4: [jarod] add module parameter gating of code addition

 drivers/net/bonding/bond_main.c | 24 ++++++++++++++++++++++++
 include/net/bonding.h           |  1 +
 2 files changed, 25 insertions(+)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 90f2615..72ab512 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -95,6 +95,7 @@ static int miimon;
 static int updelay;
 static int downdelay;
 static int use_carrier	= 1;
+static int arp_slow_switch;
 static char *mode;
 static char *primary;
 static char *primary_reselect;
@@ -133,6 +134,10 @@ MODULE_PARM_DESC(downdelay, "Delay before considering link down, "
 module_param(use_carrier, int, 0);
 MODULE_PARM_DESC(use_carrier, "Use netif_carrier_ok (vs MII ioctls) in miimon; "
 			      "0 for off, 1 for on (default)");
+module_param(arp_slow_switch, int, 0);
+MODULE_PARM_DESC(arp_slow_switch, "Do extra arp checks for switches with arp "
+				  "caches that are slow to update; "
+				  "0 for off (default), 1 for on");
 module_param(mode, charp, 0);
 MODULE_PARM_DESC(mode, "Mode of operation; 0 for balance-rr, "
 		       "1 for active-backup, 2 for balance-xor, "
@@ -2793,6 +2798,18 @@ static bool bond_ab_arp_probe(struct bonding *bond)
 			return should_notify_rtnl;
 	}
 
+	/* Sometimes the forwarding tables of the switches are not update
+	 * fast enough, so the first arp response after a slave change is
+	 * received on the wrong slave.
+	 *
+	 * The arp requests will be retried 2 times on the same slave.
+	 */
+	if (arp_slow_switch &&
+	    bond_time_in_interval(bond, curr_arp_slave->last_link_up, 2)) {
+		bond_arp_send_all(bond, curr_arp_slave);
+		return should_notify_rtnl;
+	}
+
 	bond_set_slave_inactive_flags(curr_arp_slave, BOND_SLAVE_NOTIFY_LATER);
 
 	bond_for_each_slave_rcu(bond, slave, iter) {
@@ -4280,6 +4297,12 @@ static int bond_check_params(struct bond_params *params)
 		use_carrier = 1;
 	}
 
+	if ((arp_slow_switch != 0) && (arp_slow_switch != 1)) {
+		pr_warn("Warning: arp_slow_switch module parameter (%d), not of valid value (0/1), so it was set to 1\n",
+			arp_slow_switch);
+		arp_slow_switch = 1;
+	}
+
 	if (num_peer_notif < 0 || num_peer_notif > 255) {
 		pr_warn("Warning: num_grat_arp/num_unsol_na (%d) not in range 0-255 so it was reset to 1\n",
 			num_peer_notif);
@@ -4516,6 +4539,7 @@ static int bond_check_params(struct bond_params *params)
 	params->updelay = updelay;
 	params->downdelay = downdelay;
 	params->use_carrier = use_carrier;
+	params->arp_slow_switch = arp_slow_switch;
 	params->lacp_fast = lacp_fast;
 	params->primary[0] = 0;
 	params->primary_reselect = primary_reselect_value;
diff --git a/include/net/bonding.h b/include/net/bonding.h
index c1740a2..208d31c 100644
--- a/include/net/bonding.h
+++ b/include/net/bonding.h
@@ -120,6 +120,7 @@ struct bond_params {
 	int arp_validate;
 	int arp_all_targets;
 	int use_carrier;
+	int arp_slow_switch;
 	int fail_over_mac;
 	int updelay;
 	int downdelay;
-- 
1.8.3.1