[jira] [Assigned] (YUNIKORN-2629) Adding a node can result in a deadlock

["Peter Bacsko (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/YUNIKORN-2629?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Peter Bacsko reassigned YUNIKORN-2629:
--------------------------------------

    Assignee: Peter Bacsko

> Adding a node can result in a deadlock
> --------------------------------------
>
>                 Key: YUNIKORN-2629
>                 URL: https://issues.apache.org/jira/browse/YUNIKORN-2629
>             Project: Apache YuniKorn
>          Issue Type: Bug
>          Components: shim - kubernetes
>    Affects Versions: 1.5.0
>            Reporter: Peter Bacsko
>            Assignee: Peter Bacsko
>            Priority: Blocker
>              Labels: pull-request-available
>         Attachments: updateNode_deadlock_trace.txt
>
>
> Adding a new node after Yunikorn state initialization can result in a deadlock.
> The problem is that {{Context.addNode()}} holds a lock while we're waiting for the {{NodeAccepted}} event:
> {noformat}
>        dispatcher.RegisterEventHandler(handlerID, dispatcher.EventTypeNode, func(event interface{}) {
> 		nodeEvent, ok := event.(CachedSchedulerNodeEvent)
> 		if !ok {
> 			return
> 		}
> 	        [...] removed for clarity
> 		wg.Done()
> 	})
> 	defer dispatcher.UnregisterEventHandler(handlerID, dispatcher.EventTypeNode)
> 	if err := ctx.apiProvider.GetAPIs().SchedulerAPI.UpdateNode(&si.NodeRequest{
> 		Nodes: nodesToRegister,
> 		RmID:  schedulerconf.GetSchedulerConf().ClusterID,
> 	}); err != nil {
> 		log.Log(log.ShimContext).Error("Failed to register nodes", zap.Error(err))
> 		return nil, err
> 	}
> 	// wait for all responses to accumulate
> 	wg.Wait()  <--- shim gets stuck here
>  {noformat}
> If tasks are being processed, then the dispatcher will try to retrieve the evend handler, which is returned from Context:
> {noformat}
> go func() {
> 		for {
> 			select {
> 			case event := <-getDispatcher().eventChan:
> 				switch v := event.(type) {
> 				case events.TaskEvent:
> 					getEventHandler(EventTypeTask)(v)  <--- eventually calls Context.getTask()
> 				case events.ApplicationEvent:
> 					getEventHandler(EventTypeApp)(v)
> 				case events.SchedulerNodeEvent:
> 					getEventHandler(EventTypeNode)(v)  
> {noformat}
> Since {{addNode()}} is holding a write lock, the event processing loop gets stuck, so {{registerNodes()}} will never progress.



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