[ovs-dev] [PATCH] ovn-controller: Fix busy loop when sb disconnected.

[Han Zhou]

From: Han Zhou <hzhou8 at ebay.com>

In the main loop, if the SB DB is disconnected when there is a pending
transaction, there can be busy loop causing 100% CPU of ovn-controller,
until SB DB is connected again.

The root cause is that when a transaction is pending, ovsdb_idl_loop_run()
will return NULL for ovsdb_idl_txn, and chassis_run() returns NULL when
ovnsb_idl_txn is NULL, so the condition if (br_int && chassis) is not
satisfied and so ofctrl_run() is not executed in the main loop. If there
is any message pending from br-int.mgmt, such as OFPT_BARRIER_REPLY or
OFPTYPE_ECHO_REQUEST, the main loop will be woken up again and again
because those messages are not processed because ofctrl_run() is not
invoked.

This patch fixes the problem by returning chassis_rec by chassis_run()
whenever the chassis_rec is found, even if ovnsb_idl_txn is NULL (if
ovnsb_idl_txn is NULL, it just don't do any update to the DB). With
this fix, ofctrl_run() can still be invoked even when there is a pending
transaction, so the busy loop doesn't happen any more in this situation.

Signed-off-by: Han Zhou <hzhou8 at ebay.com>
---
 ovn/controller/chassis.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/ovn/controller/chassis.c b/ovn/controller/chassis.c
index 3ea908d..8fe5565 100644
--- a/ovn/controller/chassis.c
+++ b/ovn/controller/chassis.c
@@ -82,8 +82,10 @@ chassis_run(struct ovsdb_idl_txn *ovnsb_idl_txn,
             const char *chassis_id,
             const struct ovsrec_bridge *br_int)
 {
+    const struct sbrec_chassis *chassis_rec
+        = chassis_lookup_by_name(sbrec_chassis_by_name, chassis_id);
     if (!ovnsb_idl_txn) {
-        return NULL;
+        return chassis_rec;
     }
 
     const struct ovsrec_open_vswitch *cfg;
@@ -148,8 +150,6 @@ chassis_run(struct ovsdb_idl_txn *ovnsb_idl_txn,
     ds_chomp(&iface_types, ',');
     const char *iface_types_str = ds_cstr(&iface_types);
 
-    const struct sbrec_chassis *chassis_rec
-        = chassis_lookup_by_name(sbrec_chassis_by_name, chassis_id);
     const char *encap_csum = smap_get_def(&cfg->external_ids,
                                           "ovn-encap-csum", "true");
     int n_encaps = count_1bits(req_tunnels);
-- 
2.1.0