HDFS-13731. ReencryptionUpdater fails with ConcurrentModificationException during processCheckpoints. Contributed by Zsolt Venczel.

(cherry picked from commit 3e18b957eb)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ReencryptionHandler.java

@@ -713,10 +713,10 @@ public class ReencryptionHandler implements Runnable {
           zst = new ZoneSubmissionTracker();
           submissions.put(zoneId, zst);
         }
-      }
         Future future = batchService.submit(new EDEKReencryptCallable(zoneId,
             currentBatch, reencryptionHandler));
         zst.addTask(future);
+      }
       LOG.info("Submitted batch (start:{}, size:{}) of zone {} to re-encrypt.",
           currentBatch.getFirstFilePath(), currentBatch.size(), zoneId);
       currentBatch = new ReencryptionBatch(reencryptBatchSize);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ReencryptionUpdater.java

@@ -383,6 +383,7 @@ public final class ReencryptionUpdater implements Runnable {
     final LinkedList<Future> tasks = tracker.getTasks();
     final List<XAttr> xAttrs = Lists.newArrayListWithCapacity(1);
     ListIterator<Future> iter = tasks.listIterator();
+    synchronized (handler) {
       while (iter.hasNext()) {
         Future<ReencryptionTask> curr = iter.next();
         if (curr.isCancelled()) {
@@ -403,13 +404,14 @@ public final class ReencryptionUpdater implements Runnable {
           xAttrs.clear();
           xAttrs.add(xattr);
         } catch (IOException ie) {
-        LOG.warn("Failed to update re-encrypted progress to xattr for zone {}",
-            zonePath, ie);
+          LOG.warn("Failed to update re-encrypted progress to xattr" +
+                  " for zone {}", zonePath, ie);
           ++task.numFailures;
         }
         ++tracker.numCheckpointed;
         iter.remove();
       }
+    }
     if (tracker.isCompleted()) {
       LOG.debug("Removed re-encryption tracker for zone {} because it completed"
               + " with {} tasks.", zonePath, tracker.numCheckpointed);