From b6c06c4b76ca5c206639e2ddea4f3bef393dbb11 Mon Sep 17 00:00:00 2001
From: S O'Donnell <sodonnell@cloudera.com>
Date: Fri, 9 Jul 2021 10:03:57 +0100
Subject: [PATCH] HDFS-15796. ConcurrentModificationException error happens on
 NameNode occasionally. Contributed by Daniel Ma

---
 .../server/blockmanagement/PendingReconstructionBlocks.java     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java
index acf0598639..81495ebaf2 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java
@@ -333,7 +333,7 @@ List<DatanodeStorageInfo> getTargets(BlockInfo block) {
     synchronized (pendingReconstructions) {
       PendingBlockInfo found = pendingReconstructions.get(block);
       if (found != null) {
-        return found.targets;
+        return new ArrayList<>(found.targets);
       }
     }
     return null;