YARN-11732. Fix potential NPE when calling SchedulerNode#reservedContainer for CapacityScheduler (#7065). Contributed by Tao Yang.

Reviewed-by: Syed Shameerur Rahman <syedthameem1@gmail.com>
Signed-off-by: He Xiaoqiao <hexiaoqiao@apache.org>

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/monitor/capacity/ReservedContainerCandidatesSelector.java

@@ -170,6 +170,9 @@ private NodeForPreemption getPreemptionCandidatesOnNode(
       Map<ApplicationAttemptId, Set<RMContainer>> selectedCandidates,
       Resource totalPreemptionAllowed, boolean readOnly) {
     RMContainer reservedContainer = node.getReservedContainer();
+    if (reservedContainer == null) {
+      return null;
+    }
     Resource available = Resources.clone(node.getUnallocatedResource());
     Resource totalSelected = Resources.createResource(0);
     List<RMContainer> sortedRunningContainers =

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/AbstractYarnScheduler.java

@@ -876,10 +876,9 @@ private void completeOustandingUpdatesWhichAreReserved(
       RMContainer rmContainer, ContainerStatus containerStatus,
       RMContainerEventType event) {
     N schedulerNode = getSchedulerNode(rmContainer.getNodeId());
-    if (schedulerNode != null &&
+    if (schedulerNode != null) {
-        schedulerNode.getReservedContainer() != null) {
       RMContainer resContainer = schedulerNode.getReservedContainer();
-      if (resContainer.getReservedSchedulerKey() != null) {
+      if (resContainer != null && resContainer.getReservedSchedulerKey() != null) {
         ContainerId containerToUpdate = resContainer
             .getReservedSchedulerKey().getContainerToUpdate();
         if (containerToUpdate != null &&

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/allocator/RegularContainerAllocator.java

@@ -858,12 +858,13 @@ private ContainerAllocation allocate(Resource clusterResource,
       FiCaSchedulerNode node = iter.next();
 
       // Do not schedule if there are any reservations to fulfill on the node
+      RMContainer nodeReservedContainer = node.getReservedContainer();
       if (iter.hasNext() &&
-          node.getReservedContainer() != null &&
+          nodeReservedContainer != null &&
           isSkipAllocateOnNodesWithReservedContainer()) {
         LOG.debug("Skipping scheduling on node {} since it has already been"
                 + " reserved by {}", node.getNodeID(),
-            node.getReservedContainer().getContainerId());
+            nodeReservedContainer.getContainerId());
         ActivitiesLogger.APP.recordSkippedAppActivityWithoutAllocation(
             activitiesManager, node, application, schedulerKey,
             ActivityDiagnosticConstant.NODE_HAS_BEEN_RESERVED, ActivityLevel.NODE);

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/common/fica/FiCaSchedulerApp.java

@@ -520,13 +520,13 @@ public boolean accept(Resource cluster,
             // When reserve a resource (state == NEW is for new container,
             // state == RUNNING is for increase container).
             // Just check if the node is not already reserved by someone
-            if (schedulerContainer.getSchedulerNode().getReservedContainer()
+            RMContainer reservedContainer =
-                != null) {
+                schedulerContainer.getSchedulerNode().getReservedContainer();
+            if (reservedContainer != null) {
               if (LOG.isDebugEnabled()) {
                 LOG.debug("Try to reserve a container, but the node is "
                     + "already reserved by another container="
-                    + schedulerContainer.getSchedulerNode()
+                    + reservedContainer.getContainerId());
-                    .getReservedContainer().getContainerId());
               }
               return false;
             }