HDFS-11180. Intermittent deadlock in NameNode when failover happens.

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

@@ -202,6 +202,9 @@ Release 2.7.4 - UNRELEASED
 
     HDFS-11174. Wrong HttpFS test command in doc. (John Zhuge via aajisaka)
 
+    HDFS-11180. Intermittent deadlock in NameNode when failover happens.
+    (aajisaka)
+
 Release 2.7.3 - 2016-08-25
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml

@@ -128,6 +128,33 @@
         <Class name="org.apache.hadoop.hdfs.server.namenode.FSEditLog" />
         <Field name="journalSet" />
         <Bug pattern="IS2_INCONSISTENT_SYNC" />
+    </Match>
+    <!--
+      FSEditLog#getTotalSyncCount is not synchronized because this method is
+      used by metrics. NullPointerException can happen and it is ignored.
+    -->
+    <Match>
+      <Class name="org.apache.hadoop.hdfs.server.namenode.FSEditLog" />
+      <Field name="editLogStream" />
+      <Bug pattern="IS2_INCONSISTENT_SYNC" />
+    </Match>
+    <!--
+      FSEditLog#isOpenForWriteWithoutLock and FSEditLog#isSegmentOpenWithoutLock
+      are not synchronized because these methods are used by metrics.
+    -->
+    <Match>
+      <Class name="org.apache.hadoop.hdfs.server.namenode.FSEditLog" />
+      <Field name="state" />
+      <Bug pattern="IS2_INCONSISTENT_SYNC" />
+    </Match>
+    <!--
+      All of the threads which update/increment txid are synchronized,
+      so make txid volatile instead of AtomicLong.
+    -->
+    <Match>
+      <Class name="org.apache.hadoop.hdfs.server.namenode.FSEditLog" />
+      <Field name="txid" />
+      <Bug pattern="VO_VOLATILE_INCREMENT" />
     </Match>
      <!--
       This method isn't performance-critical and is much clearer to write as it's written.

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

@@ -153,14 +153,16 @@ public class FSEditLog implements LogsPurgeable {
   private EditLogOutputStream editLogStream = null;
 
   // a monotonically increasing counter that represents transactionIds.
-  private long txid = 0;
+  // All of the threads which update/increment txid are synchronized,
+  // so make txid volatile instead of AtomicLong.
+  private volatile long txid = 0;
 
   // stores the last synced transactionId.
   private long synctxid = 0;
 
   // the first txid of the log that's currently open for writing.
   // If this value is N, we are currently writing to edits_inprogress_N
-  private long curSegmentTxId = HdfsConstants.INVALID_TXID;
+  private volatile long curSegmentTxId = HdfsConstants.INVALID_TXID;
 
   // the time of printing the statistics to the log file.
   private long lastPrintTime;
@@ -331,7 +333,18 @@ public class FSEditLog implements LogsPurgeable {
     return state == State.IN_SEGMENT ||
       state == State.BETWEEN_LOG_SEGMENTS;
   }
-  
+
+  /**
+   * Return true if the log is currently open in write mode.
+   * This method is not synchronized and must be used only for metrics.
+   * @return true if the log is currently open in write mode, regardless
+   * of whether it actually has an open segment.
+   */
+  boolean isOpenForWriteWithoutLock() {
+    return state == State.IN_SEGMENT ||
+        state == State.BETWEEN_LOG_SEGMENTS;
+  }
+
   /**
    * @return true if the log is open in write mode and has a segment open
    * ready to take edits.
@@ -340,6 +353,16 @@ public class FSEditLog implements LogsPurgeable {
     return state == State.IN_SEGMENT;
   }
 
+  /**
+   * Return true the state is IN_SEGMENT.
+   * This method is not synchronized and must be used only for metrics.
+   * @return true if the log is open in write mode and has a segment open
+   * ready to take edits.
+   */
+  boolean isSegmentOpenWithoutLock() {
+    return state == State.IN_SEGMENT;
+  }
+
   /**
    * @return true if the log is open in read mode.
    */
@@ -513,7 +536,16 @@ public class FSEditLog implements LogsPurgeable {
   public synchronized long getLastWrittenTxId() {
     return txid;
   }
-  
+
+  /**
+   * Return the transaction ID of the last transaction written to the log.
+   * This method is not synchronized and must be used only for metrics.
+   * @return The transaction ID of the last transaction written to the log
+   */
+  long getLastWrittenTxIdWithoutLock() {
+    return txid;
+  }
+
   /**
    * @return the first transaction ID in the current log segment
    */
@@ -522,7 +554,16 @@ public class FSEditLog implements LogsPurgeable {
         "Bad state: %s", state);
     return curSegmentTxId;
   }
-  
+
+  /**
+   * Return the first transaction ID in the current log segment.
+   * This method is not synchronized and must be used only for metrics.
+   * @return The first transaction ID in the current log segment
+   */
+  long getCurSegmentTxIdWithoutLock() {
+    return curSegmentTxId;
+  }
+
   /**
    * Set the transaction ID to use for the next transaction written.
    */
@@ -1166,7 +1207,9 @@ public class FSEditLog implements LogsPurgeable {
   /**
    * Get all the journals this edit log is currently operating on.
    */
-  synchronized List<JournalAndStream> getJournals() {
+  List<JournalAndStream> getJournals() {
+    // The list implementation is CopyOnWriteArrayList,
+    // so we don't need to synchronize this method.
     return journalSet.getAllJournalStreams();
   }
   
@@ -1174,7 +1217,7 @@ public class FSEditLog implements LogsPurgeable {
    * Used only by tests.
    */
   @VisibleForTesting
-  synchronized public JournalSet getJournalSet() {
+  public JournalSet getJournalSet() {
     return journalSet;
   }
   

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

@@ -1003,7 +1003,7 @@ public class FSImage implements Closeable {
       Canceler canceler) throws IOException {
     FSImageCompression compression =
         FSImageCompression.createCompression(conf);
-    long txid = getLastAppliedOrWrittenTxId();
+    long txid = getCorrectLastAppliedOrWrittenTxId();
     SaveNamespaceContext ctx = new SaveNamespaceContext(source, txid,
         canceler);
     FSImageFormat.Saver saver = new FSImageFormat.Saver(ctx);
@@ -1101,7 +1101,7 @@ public class FSImage implements Closeable {
     if (editLogWasOpen) {
       editLog.endCurrentLogSegment(true);
     }
-    long imageTxId = getLastAppliedOrWrittenTxId();
+    long imageTxId = getCorrectLastAppliedOrWrittenTxId();
     if (!addToCheckpointing(imageTxId)) {
       throw new IOException(
           "FS image is being downloaded from another NN at txid " + imageTxId);
@@ -1463,6 +1463,15 @@ public class FSImage implements Closeable {
   }
 
   public long getLastAppliedOrWrittenTxId() {
+    return Math.max(lastAppliedTxId,
+        editLog != null ? editLog.getLastWrittenTxIdWithoutLock() : 0);
+  }
+
+  /**
+   * This method holds a lock of FSEditLog to get the correct value.
+   * This method must not be used for metrics.
+   */
+  public long getCorrectLastAppliedOrWrittenTxId() {
     return Math.max(lastAppliedTxId,
         editLog != null ? editLog.getLastWrittenTxId() : 0);
   }

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

@@ -4516,7 +4516,7 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
       //create ha status
       final NNHAStatusHeartbeat haState = new NNHAStatusHeartbeat(
           haContext.getState().getServiceState(),
-          getFSImage().getLastAppliedOrWrittenTxId());
+          getFSImage().getCorrectLastAppliedOrWrittenTxId());
 
       return new HeartbeatResponse(cmds, haState, rollingUpgradeInfo);
     } finally {
@@ -4775,17 +4775,17 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
   @Metric({"TransactionsSinceLastLogRoll",
       "Number of transactions since last edit log roll"})
   public long getTransactionsSinceLastLogRoll() {
-    if (isInStandbyState() || !getEditLog().isSegmentOpen()) {
+    if (isInStandbyState() || !getEditLog().isSegmentOpenWithoutLock()) {
       return 0;
     } else {
-      return getEditLog().getLastWrittenTxId() -
+      return getEditLog().getLastWrittenTxIdWithoutLock() -
-        getEditLog().getCurSegmentTxId() + 1;
+          getEditLog().getCurSegmentTxIdWithoutLock() + 1;
     }
   }
-  
+
   @Metric({"LastWrittenTransactionId", "Transaction ID written to the edit log"})
   public long getLastWrittenTransactionId() {
-    return getEditLog().getLastWrittenTxId();
+    return getEditLog().getLastWrittenTxIdWithoutLock();
   }
   
   @Metric({"LastCheckpointTime",
@@ -7102,7 +7102,9 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
     List<Map<String, String>> jasList = new ArrayList<Map<String, String>>();
     FSEditLog log = getFSImage().getEditLog();
     if (log != null) {
-      boolean openForWrite = log.isOpenForWrite();
+      // This flag can be false because we cannot hold a lock of FSEditLog
+      // for metrics.
+      boolean openForWrite = log.isOpenForWriteWithoutLock();
       for (JournalAndStream jas : log.getJournals()) {
         final Map<String, String> jasMap = new HashMap<String, String>();
         String manager = jas.getManager().toString();

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

@@ -1104,7 +1104,7 @@ class NameNodeRpcServer implements NamenodeProtocols {
     checkNNStartup();
     namesystem.checkOperation(OperationCategory.UNCHECKED);
     namesystem.checkSuperuserPrivilege();
-    return namesystem.getFSImage().getLastAppliedOrWrittenTxId();
+    return namesystem.getFSImage().getCorrectLastAppliedOrWrittenTxId();
   }
   
   @Override // NamenodeProtocol

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

@@ -165,7 +165,7 @@ public class StandbyCheckpointer {
       FSImage img = namesystem.getFSImage();
       
       long prevCheckpointTxId = img.getStorage().getMostRecentCheckpointTxId();
-      long thisCheckpointTxId = img.getLastAppliedOrWrittenTxId();
+      long thisCheckpointTxId = img.getCorrectLastAppliedOrWrittenTxId();
       assert thisCheckpointTxId >= prevCheckpointTxId;
       if (thisCheckpointTxId == prevCheckpointTxId) {
         LOG.info("A checkpoint was triggered but the Standby Node has not " +
@@ -253,7 +253,7 @@ public class StandbyCheckpointer {
 
   private long countUncheckpointedTxns() {
     FSImage img = namesystem.getFSImage();
-    return img.getLastAppliedOrWrittenTxId() -
+    return img.getCorrectLastAppliedOrWrittenTxId() -
       img.getStorage().getMostRecentCheckpointTxId();
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSNamesystemMBean.java

@@ -159,4 +159,28 @@ public class TestFSNamesystemMBean {
       }
     }
   }
+
+  // The test makes sure JMX request can be processed even if FSEditLog
+  // is synchronized.
+  @Test
+  public void testWithFSEditLogLock() throws Exception {
+    Configuration conf = new Configuration();
+    MiniDFSCluster cluster = null;
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).build();
+      cluster.waitActive();
+      synchronized (cluster.getNameNode().getFSImage().getEditLog()) {
+        MBeanClient client = new MBeanClient();
+        client.start();
+        client.join(20000);
+        assertTrue("JMX calls are blocked when FSEditLog" +
+            " is synchronized by another thread", client.succeeded);
+        client.interrupt();
+      }
+    } finally {
+      if (cluster != null) {
+        cluster.shutdown();
+      }
+    }
+  }
 }