elastic_7.13.3.patch

diff --git a/server/src/main/java/org/elasticsearch/tasks/TaskManager.java b/server/src/main/java/org/elasticsearch/tasks/TaskManager.java
index 10fb4eced77..4be7707d886 100644
--- a/server/src/main/java/org/elasticsearch/tasks/TaskManager.java
+++ b/server/src/main/java/org/elasticsearch/tasks/TaskManager.java
@@ -81,6 +81,8 @@ public class TaskManager implements ClusterStateApplier {
 
     private final ConcurrentMapLong<CancellableTaskHolder> cancellableTasks = ConcurrentCollections
         .newConcurrentMapLongWithAggressiveConcurrency();
+    private final ConcurrentMapLong<Set<CancellableTaskHolder>> cancellableChildTasks = ConcurrentCollections
+        .newConcurrentMapLongWithAggressiveConcurrency();
 
     private final AtomicLong taskIdGenerator = new AtomicLong();
 
@@ -147,6 +149,19 @@ public class TaskManager implements ClusterStateApplier {
         CancellableTask cancellableTask = (CancellableTask) task;
         CancellableTaskHolder holder = new CancellableTaskHolder(cancellableTask);
         CancellableTaskHolder oldHolder = cancellableTasks.put(task.getId(), holder);
+        TaskId parent_id = task.getParentTaskId();
+        if (parent_id.isSet())
+        {
+            if (cancellableChildTasks.containsKey(parent_id.getId()))
+                cancellableChildTasks.get(parent_id.getId()).add(holder);
+            else
+            {
+                HashSet<CancellableTaskHolder> a = new HashSet<>();
+                a.add(holder);
+                cancellableChildTasks.put(parent_id.getId(), a);
+            }
+        }
+
         assert oldHolder == null;
         // Check if this task was banned before we start it. The empty check is used to avoid
         // computing the hash code of the parent taskId as most of the time bannedParents is empty.
@@ -188,6 +203,8 @@ public class TaskManager implements ClusterStateApplier {
         logger.trace("unregister task for id: {}", task.getId());
         if (task instanceof CancellableTask) {
             CancellableTaskHolder holder = cancellableTasks.remove(task.getId());
+            if (task.getParentTaskId().isSet())
+                cancellableChildTasks.get(task.getParentTaskId().getId()).remove(holder);
             if (holder != null) {
                 holder.finish();
                 return holder.getTask();
@@ -372,10 +389,12 @@ public class TaskManager implements ClusterStateApplier {
                 }
             }
         }
-        return cancellableTasks.values().stream()
-            .filter(t -> t.hasParent(parentTaskId))
-            .map(t -> t.task)
-            .collect(Collectors.toList());
+        if (cancellableChildTasks.containsKey(parentTaskId.getId()))
+            return cancellableChildTasks.get(parentTaskId.getId()).stream()
+                .map(t -> t.task)
+                .collect(Collectors.toList());
+        else
+            return Collections.emptyList();
     }
 
     /**