OVN: Fix the ovn-controller 100% usage issue with put_mac_bindings

ISSUE:
a. As soon as entries get added to put_mac_bindings in pinctrl.c,
   ovn-controller CPU consumption reached 100%.

b. This happens because in wait_put_mac_bindings,
   if !hmap_is_empty(&put_mac_bindings) succeeds and
   calls poll_immediat_wake().

   ovn-controller.log:
   "2019-05-10T19:43:28.035Z|00035|poll_loop|INFO|wakeup due to
    0-ms timeout at ovn/controller/pinctrl.c:2520 (99% CPU usage)"

ROOT_CAUSE:
a. Earlier it used to work fine, because in run_put_mac_bindings
   all the bindings in put_mac_bindings would be flushed.

b. As a part of adding a new thread in pinctrl, this
   line got replaced with calling buffer_put_mac_bindings.

    "
    .
    .
    .
       /* Move the mac bindings from 'put_mac_bindings' hmap to
     * 'buffered_mac_bindings' and notify the pinctrl_handler.
     * pinctrl_handler will reinject the buffered packets. */
    if (!hmap_is_empty(&put_mac_bindings)) {
        buffer_put_mac_bindings();
        notify_pinctrl_handler();
    }
    "

    And buffer_put_mac_binding would pop the bindings from
    put_mac_bindings, thereby emptying it.

c.  However, 1c24b2f
    changed the buffer dequeueing logic and in the process
    removed buffer_put_mac_binding, as a result put_mac_bindings
    would never get empty.

FIX:
a. Added call to flush_put_mac_bindings back in
   run_put_mac_bindings.

b. Additionally, updated the documentation in pinctrl.c to
   reflect the new buffer dequeueing logic added by
   1c24b2f.

Signed-off-by: Ankur Sharma <ankur.sharma@nutanix.com>
Reported-by: Ankur Sharma <ankur.sharma@nutanix.com>
CC: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Fixes: 1c24b2f ("OVN: fix pinctrl ip buffering for gw router port")
Signed-off-by: 0-day Robot <robot@bytheb.org>

ovn/controller/pinctrl.c

@@ -91,11 +91,13 @@ VLOG_DEFINE_THIS_MODULE(pinctrl);
  *
  *   - arp/nd_ns      - These actions generate an ARP/IPv6 Neighbor solicit
  *                      requests. The original packets are buffered and
- *                      injected back when put_arp/put_nd actions are called.
+ *                      injected back when put_arp/put_nd resolves
+ *                      corresponding ARP/IPv6 Neighbor solicit requests.
  *                      When pinctrl_run(), writes the mac bindings from the
  *                      'put_mac_bindings' hmap to the MAC_Binding table in
- *                      SB DB, it moves these mac bindings to another hmap -
- *                      'buffered_mac_bindings'.
+ *                      SB DB, run_buffered_binding will add the buffered
+ *                      packets to buffered_mac_bindings and notify
+ *                      pinctrl_handler.
  *
  *                      The pinctrl_handler thread calls the function -
  *                      send_mac_binding_buffered_pkts(), which uses
@@ -2468,6 +2470,7 @@ run_put_mac_bindings(struct ovsdb_idl_txn *ovnsb_idl_txn,
                             sbrec_mac_binding_by_lport_ip,
                             pmb);
     }
+    flush_put_mac_bindings();
 }
 
 static void