HDFS-8099. Change "DFSInputStream has been closed already" message to debug log level (Charles Lamb via Colin P. McCabe)

(cherry picked from commit 30acb7372ab97adf9bc86ead529c96cfe36e2396)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -13,6 +13,9 @@ Release 2.7.2 - UNRELEASED
     HADOOP-5323. Trash documentation should describe its directory structure and
     configurations. (Weiwei Yang via ozawa)
 
+    HDFS-8099. Change "DFSInputStream has been closed already" message to
+    debug log level (Charles Lamb via Colin P. McCabe)
+
   OPTIMIZATIONS
 
     HDFS-8722. Optimize datanode writes for small writes and flushes (kihwal)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java

@@ -666,7 +666,7 @@ implements ByteBufferReadable, CanSetDropBehind, CanSetReadahead,
   @Override
   public synchronized void close() throws IOException {
     if (!closed.compareAndSet(false, true)) {
-      DFSClient.LOG.warn("DFSInputStream has been closed already");
+      DFSClient.LOG.debug("DFSInputStream has been closed already");
       return;
     }
     dfsClient.checkOpen();