Pre Ready-For-Testing Checklist

• Where is the reproduce steps/test steps documented?
  The reproduce steps/test steps are at:

1. Launch a large backing image and check the BackingImageDatasource POD should be launched
   • Create a large size volume, and create backing image via Export from a Longhorn volume
2. Block all ingress and outgress package with applying network policy, check the progress status should be paused after few seconds.

   kind: NetworkPolicy
   apiVersion: networking.k8s.io/v1
   metadata:
     name: deny-pod-all-packages
     namespace: longhorn-system
   spec:
     podSelector:
       matchLabels:
         longhorn.io/backing-image-data-source: <your-backing-image-name>
         longhorn.io/component: backing-image-data-source
     policyTypes:
     - Ingress
     - Egress

3. Check the logs of the longhorn manager pod, it should not show the error panic: close of closed channel. And after the monitoring is stopped because it cannot connect to the data source POD, the next round of monitoring will continue.
   

• Is there a workaround for the issue? If so, where is it documented?
  The workaround is at:
  Since the lognhorn manager POD will panic and restart automatically, it will resume normal if the BackingImageDatasource POD is recovered.

• Does the PR include the explanation for the fix or the feature?
  fix: Check if the channel has been closed before closing longhorn-manager#1590 (comment)

• Have the backend code been merged (Manager, Engine, Instance Manager, BackupStore etc) (including backport-needed/*)?
  The PR is at [BACKPORT][v1.3.3] fix: Notify by sending a signal to stop instead of using close channel longhorn-manager#1591

@weizhe0422 the verification step is wrong? Should be below

Check the log of longhorn manager pod, there should "not" show the error panic: close of closed channel. And after the monitoring is stopped due to failure to connect to the data source POD, the next round of monitoring will continue.

@innobead It is my mistake that missed the word "not". I will pay more attention next time. Thank you.

Verified in longhorn v1.3.x b2c607 with test steps
Result Pass

1. After backing image creation progress paused by new netwoklpolicy, in longhorn-manager pod can observe new round monitor started, also close of closed channel not found in manager log.
2. After delete the network policy, create volume form backing image, that volume created successfully and can attach to node.

time="2022-12-09T05:43:37Z" level=info msg="Stopped monitoring" backingImageDataSource=vol2 controller=longhorn-backing-image-data-source node=ip-172-31-31-137
time="2022-12-09T05:43:44Z" level=info msg="Start monitoring" backingImageDataSource=vol2 controller=longhorn-backing-image-data-source diskUUID=6fd1c78c-6b4c-4fed-8fee-21cd772f87d3 node=ip-172-31-31-137 nodeID=ip-172-31-31-137 parameters="map[export-type:raw volume-name:vol1]" sourceType=export-from-volume