From e0fa49234fd37aca88e1caa95bac77bca192bae4 Mon Sep 17 00:00:00 2001
From: Akira Ajisaka <aajisaka@apache.org>
Date: Thu, 1 Dec 2016 23:08:59 +0900
Subject: [PATCH] HDFS-11180. Intermittent deadlock in NameNode when failover
 happens.

---
 .../dev-support/findbugsExcludeFile.xml       | 27 +++++++
 .../hdfs/server/namenode/FSEditLog.java       | 72 ++++++++++++++++---
 .../hadoop/hdfs/server/namenode/FSImage.java  | 15 +++-
 .../hdfs/server/namenode/FSNamesystem.java    | 27 +++++--
 .../server/namenode/NameNodeRpcServer.java    |  2 +-
 .../namenode/ha/StandbyCheckpointer.java      |  4 +-
 .../namenode/TestFSNamesystemMBean.java       | 24 +++++++
 7 files changed, 148 insertions(+), 23 deletions(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml b/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml
index 426fb72d71..e6e4057bff 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml
+++ b/hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml
@@ -108,6 +108,33 @@
         <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.
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java
index ef9eb68659..c9ee32b39b 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java
@@ -155,14 +155,16 @@ private enum State {
   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 = HdfsServerConstants.INVALID_TXID;
+  private volatile long curSegmentTxId = HdfsServerConstants.INVALID_TXID;
 
   // the time of printing the statistics to the log file.
   private long lastPrintTime;
@@ -338,7 +340,18 @@ synchronized boolean isOpenForWrite() {
     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.
@@ -347,6 +360,16 @@ synchronized boolean isSegmentOpen() {
     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.
    */
@@ -522,7 +545,16 @@ private void endTransaction(long start) {
   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
    */
@@ -531,7 +563,16 @@ synchronized long getCurSegmentTxId() {
         "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.
    */
@@ -1182,7 +1223,9 @@ void logRemoveXAttrs(String src, List<XAttr> xAttrs, boolean toLogRpcIds) {
   /**
    * 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();
   }
   
@@ -1190,7 +1233,7 @@ synchronized List<JournalAndStream> getJournals() {
    * Used only by tests.
    */
   @VisibleForTesting
-  synchronized public JournalSet getJournalSet() {
+  public JournalSet getJournalSet() {
     return journalSet;
   }
   
@@ -1731,11 +1774,18 @@ public void restart() {
    * Return total number of syncs happened on this edit log.
    * @return long - count
    */
-  public synchronized long getTotalSyncCount() {
-    if (editLogStream != null) {
-      return editLogStream.getNumSync();
-    } else {
+  public long getTotalSyncCount() {
+    // Avoid NPE as possible.
+    if (editLogStream == null) {
       return 0;
     }
+    long count = 0;
+    try {
+      count = editLogStream.getNumSync();
+    } catch (NullPointerException ignore) {
+      // This method is used for metrics, so we don't synchronize it.
+      // Therefore NPE can happen even if there is a null check before.
+    }
+    return count;
   }
 }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java
index d02a6ca81e..c40c626d16 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSImage.java
@@ -924,7 +924,7 @@ public void saveLegacyOIVImage(FSNamesystem source, String targetDir,
       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);
@@ -1019,7 +1019,7 @@ public synchronized boolean saveNamespace(long timeWindow, long txGap,
       final long checkpointTxId = image.getCheckpointTxId();
       final long checkpointAge = Time.now() - imageFile.lastModified();
       if (checkpointAge <= timeWindow * 1000 &&
-          checkpointTxId >= this.getLastAppliedOrWrittenTxId() - txGap) {
+          checkpointTxId >= this.getCorrectLastAppliedOrWrittenTxId() - txGap) {
         return false;
       }
     }
@@ -1046,7 +1046,7 @@ public synchronized void saveNamespace(FSNamesystem source, NameNodeFile nnf,
     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);
@@ -1417,6 +1417,15 @@ public synchronized long getLastAppliedTxId() {
   }
 
   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);
   }
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
index c78ef465a9..8a750a06ce 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
@@ -3654,7 +3654,7 @@ nodeReg, reports, getBlockPoolId(), cacheCapacity, cacheUsed,
       //create ha status
       final NNHAStatusHeartbeat haState = new NNHAStatusHeartbeat(
           haContext.getState().getServiceState(),
-          getFSImage().getLastAppliedOrWrittenTxId());
+          getFSImage().getCorrectLastAppliedOrWrittenTxId());
 
       return new HeartbeatResponse(cmds, haState, rollingUpgradeInfo,
           blockReportLeaseId);
@@ -3779,7 +3779,7 @@ public NameNodeEditLogRoller(long rollThreshold, int sleepIntervalMs) {
     public void run() {
       while (fsRunning && shouldRun) {
         try {
-          long numEdits = getTransactionsSinceLastLogRoll();
+          long numEdits = getCorrectTransactionsSinceLastLogRoll();
           if (numEdits > rollThreshold) {
             FSNamesystem.LOG.info("NameNode rolling its own edit log because"
                 + " number of edits in open segment exceeds threshold of "
@@ -3928,17 +3928,30 @@ public long getTransactionsSinceLastCheckpoint() {
   @Metric({"TransactionsSinceLastLogRoll",
       "Number of transactions since last edit log roll"})
   public long getTransactionsSinceLastLogRoll() {
+    if (isInStandbyState() || !getEditLog().isSegmentOpenWithoutLock()) {
+      return 0;
+    } else {
+      return getEditLog().getLastWrittenTxIdWithoutLock() -
+          getEditLog().getCurSegmentTxIdWithoutLock() + 1;
+    }
+  }
+
+  /**
+   * Get the correct number of transactions since last edit log roll.
+   * This method holds a lock of FSEditLog and must not be used for metrics.
+   */
+  private long getCorrectTransactionsSinceLastLogRoll() {
     if (isInStandbyState() || !getEditLog().isSegmentOpen()) {
       return 0;
     } else {
       return getEditLog().getLastWrittenTxId() -
-        getEditLog().getCurSegmentTxId() + 1;
+          getEditLog().getCurSegmentTxId() + 1;
     }
   }
-  
+
   @Metric({"LastWrittenTransactionId", "Transaction ID written to the edit log"})
   public long getLastWrittenTransactionId() {
-    return getEditLog().getLastWrittenTxId();
+    return getEditLog().getLastWrittenTxIdWithoutLock();
   }
   
   @Metric({"LastCheckpointTime",
@@ -5613,7 +5626,9 @@ public String getNameJournalStatus() {
     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();
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeRpcServer.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeRpcServer.java
index c55c4d1110..0fc3e60f7e 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeRpcServer.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeRpcServer.java
@@ -1215,7 +1215,7 @@ public long getTransactionID() throws IOException {
     checkNNStartup();
     namesystem.checkOperation(OperationCategory.UNCHECKED);
     namesystem.checkSuperuserPrivilege();
-    return namesystem.getFSImage().getLastAppliedOrWrittenTxId();
+    return namesystem.getFSImage().getCorrectLastAppliedOrWrittenTxId();
   }
   
   @Override // NamenodeProtocol
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/StandbyCheckpointer.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/StandbyCheckpointer.java
index 099a6aa776..569c6bf55d 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/StandbyCheckpointer.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/StandbyCheckpointer.java
@@ -172,7 +172,7 @@ private void doCheckpoint(boolean sendCheckpoint) throws InterruptedException, I
       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 " +
@@ -315,7 +315,7 @@ static int getCanceledCount() {
 
   private long countUncheckpointedTxns() {
     FSImage img = namesystem.getFSImage();
-    return img.getLastAppliedOrWrittenTxId() -
+    return img.getCorrectLastAppliedOrWrittenTxId() -
       img.getStorage().getMostRecentCheckpointTxId();
   }
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSNamesystemMBean.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSNamesystemMBean.java
index 4687cfdfe9..d3114943a5 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSNamesystemMBean.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSNamesystemMBean.java
@@ -162,6 +162,30 @@ public void testWithFSNamesystemWriteLock() throws Exception {
     }
   }
 
+  // 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();
+      }
+    }
+  }
+
   @Test(timeout = 120000)
   public void testFsEditLogMetrics() throws Exception {
     final Configuration conf = new Configuration();