HDFS-12137. DN dataset lock should be fair. Contributed by Daryn Sharp.

(cherry picked from commit a47820d72a4c4aba857fd7325fa9ae9a95fe8faa)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java

@@ -127,6 +127,7 @@ import org.apache.hadoop.util.Time;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
+import java.util.concurrent.locks.ReentrantLock;
 
 /**************************************************
  * FSDataset manages a set of data blocks.  Each block
@@ -287,6 +288,7 @@ class FsDatasetImpl implements FsDatasetSpi<FsVolumeImpl> {
     this.smallBufferSize = DFSUtilClient.getSmallBufferSize(conf);
     this.datasetLock = new AutoCloseableLock(
         new InstrumentedLock(getClass().getName(), LOG,
+          new ReentrantLock(true),
           conf.getTimeDuration(
             DFSConfigKeys.DFS_LOCK_SUPPRESS_WARNING_INTERVAL_KEY,
             DFSConfigKeys.DFS_LOCK_SUPPRESS_WARNING_INTERVAL_DEFAULT,