put mutex around installplan creation

pkg/controller/operators/catalog/operator.go

@@ -116,6 +116,7 @@ type Operator struct {
  installPlanTimeout time.Duration
  bundleUnpackTimeout time.Duration
  clientFactory clients.Factory
+ muInstallPlan sync.Mutex
 }
 
 type CatalogSourceSyncFunc func(logger *logrus.Entry, in *v1alpha1.CatalogSource) (out *v1alpha1.CatalogSource, continueSync bool, syncError error)
@@ -1167,6 +1168,26 @@ func (o *Operator) ensureInstallPlan(logger *logrus.Entry, namespace string, gen
  return nil, err
  }
 
+ // There are multiple(2) worker threads process the namespaceQueue.
+ // Both worker can work at the same time when 2 separate updates are made for the namespace.
+ // The following sequence causes 2 installplans are created for a subscription
+ // 1. worker 1 doesn't find the installplan
+ // 2. worker 2 doesn't find the installplan
+ // 3. both worker 1 and 2 create the installplan
+ //
+ // This lock prevents the step 2 in the sequence so that only one installplan is created for a subscription.
+ // The sequence is like the following with this lock
+ // 1. worker 1 locks
+ // 2. worker 1 doesn't find the installplan
+ // 3. worker 2 wait for unlock <--- difference
+ // 4. worker 1 creates the installplan
+ // 5. worker 1 unlocks
+ // 6. worker 2 locks
+ // 7. worker 2 finds the installplan <--- difference
+ // 8. worker 2 unlocks
+ o.muInstallPlan.Lock()
+ defer o.muInstallPlan.Unlock()
+
  for _, installPlan := range installPlans {
  if installPlan.Spec.Generation == gen {
  return reference.GetReference(installPlan)