HDFS-16939. Fix the thread safety bug in LowRedundancyBlocks. (#5450). Contributed by Shuyan Zhang.

Signed-off-by: He Xiaoqiao <hexiaoqiao@apache.org>

Author: zhangshuyan0

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/LowRedundancyBlocks.java

@@ -86,10 +86,10 @@ class LowRedundancyBlocks implements Iterable<BlockInfo> {
  private final List<LightWeightLinkedSet<BlockInfo>> priorityQueues
  = new ArrayList<>(LEVEL);
 
- /** The number of corrupt blocks with replication factor 1 */
 
  private final LongAdder lowRedundancyBlocks = new LongAdder();
  private final LongAdder corruptBlocks = new LongAdder();
+ /** The number of corrupt blocks with replication factor 1 */
  private final LongAdder corruptReplicationOneBlocks = new LongAdder();
  private final LongAdder lowRedundancyECBlockGroups = new LongAdder();
  private final LongAdder corruptECBlockGroups = new LongAdder();
@@ -369,11 +369,11 @@ synchronized boolean remove(BlockInfo block,
  * @return true if the block was found and removed from one of the priority
  * queues
  */
- boolean remove(BlockInfo block, int priLevel) {
+ synchronized boolean remove(BlockInfo block, int priLevel) {
  return remove(block, priLevel, block.getReplication());
  }
 
- boolean remove(BlockInfo block, int priLevel, int oldExpectedReplicas) {
+ synchronized boolean remove(BlockInfo block, int priLevel, int oldExpectedReplicas) {
  if(priLevel >= 0 && priLevel < LEVEL
  && priorityQueues.get(priLevel).remove(block)) {
  NameNode.blockStateChangeLog.debug(