[YARN-8233] NPE in CapacityScheduler#tryCommit when handling allocate/reserve proposal whose allocatedOrReservedContainer is null

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 3.2.0
• Fix Version/s: 2.10.0, 2.9.2, 3.0.4, 3.1.2, 3.3.0, 3.2.1
• Component/s: capacityscheduler
• Target Version/s: 2.10.0, 2.9.2, 3.0.4, 3.1.2, 3.3.0, 3.2.1
• Hadoop Flags: Reviewed
• Assignee: Tao Yang
• Reporter: Tao Yang
• Created: 28/Apr/18 07:08
• Updated: 28/Nov/18 14:15
• Resolved: 10/Nov/18 12:54

Description

Recently we saw a NPE problem in CapacityScheduler#tryCommit when try to find the attemptId by calling c.getAllocatedOrReservedContainer().get... from an allocate/reserve proposal. But got null allocatedOrReservedContainer and thrown NPE.
Reference code:

    // find the application to accept and apply the ResourceCommitRequest
    if (request.anythingAllocatedOrReserved()) {
      ContainerAllocationProposal<FiCaSchedulerApp, FiCaSchedulerNode> c =
          request.getFirstAllocatedOrReservedContainer();
      attemptId =
          c.getAllocatedOrReservedContainer().getSchedulerApplicationAttempt()
              .getApplicationAttemptId();   //NPE happens here
    } else { ...

The proposal was constructed in CapacityScheduler#createResourceCommitRequest and allocatedOrReservedContainer is possibly null in async-scheduling process when node was lost or application was finished (details in CapacityScheduler#getSchedulerContainer).
Reference code:

      // Allocated something
      List<AssignmentInformation.AssignmentDetails> allocations =
          csAssignment.getAssignmentInformation().getAllocationDetails();
      if (!allocations.isEmpty()) {
        RMContainer rmContainer = allocations.get(0).rmContainer;
        allocated = new ContainerAllocationProposal<>(
            getSchedulerContainer(rmContainer, true),   //possibly null
            getSchedulerContainersToRelease(csAssignment),
            getSchedulerContainer(csAssignment.getFulfilledReservedContainer(),
                false), csAssignment.getType(),
            csAssignment.getRequestLocalityType(),
            csAssignment.getSchedulingMode() != null ?
                csAssignment.getSchedulingMode() :
                SchedulingMode.RESPECT_PARTITION_EXCLUSIVITY,
            csAssignment.getResource());
      }

I think we should add null check for allocateOrReserveContainer before create allocate/reserve proposals. Besides the allocation process has increase unconfirmed resource of app when creating an allocate assignment, so if this check is null, we should decrease the unconfirmed resource of live app.