HBASE-20921 Possible NPE in ReopenTableRegionsProcedure

hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionStates.java

@@ -643,6 +643,12 @@ public class RegionStates {
    */
   public HRegionLocation checkReopened(HRegionLocation oldLoc) {
     RegionStateNode node = getRegionStateNode(oldLoc.getRegion());
+    // HBASE-20921
+    // if the oldLoc's state node does not exist, that means the region is
+    // merged or split, no need to check it
+    if (node == null) {
+      return null;
+    }
     synchronized (node) {
       if (oldLoc.getSeqNum() >= 0) {
         // in OPEN state before

hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/ReopenTableRegionsProcedure.java

@@ -124,7 +124,7 @@ public class ReopenTableRegionsProcedure
   @Override
   protected void rollbackState(MasterProcedureEnv env, ReopenTableRegionsState state)
       throws IOException, InterruptedException {
-    throw new UnsupportedOperationException();
+    throw new UnsupportedOperationException("unhandled state=" + state);
   }
 
   @Override

hbase-server/src/test/java/org/apache/hadoop/hbase/master/assignment/TestModifyTableWhileMerging.java

@@ -0,0 +1,109 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.master.assignment;
+
+import java.util.List;
+
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.HBaseTestingUtility;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.client.Admin;
+import org.apache.hadoop.hbase.client.RegionInfo;
+import org.apache.hadoop.hbase.client.Table;
+import org.apache.hadoop.hbase.client.TableDescriptor;
+import org.apache.hadoop.hbase.master.procedure.MasterProcedureConstants;
+import org.apache.hadoop.hbase.master.procedure.MasterProcedureEnv;
+import org.apache.hadoop.hbase.master.procedure.ModifyTableProcedure;
+import org.apache.hadoop.hbase.procedure2.ProcedureExecutor;
+import org.apache.hadoop.hbase.testclassification.MasterTests;
+import org.apache.hadoop.hbase.testclassification.MediumTests;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hadoop.hbase.shaded.protobuf.generated.ProcedureProtos;
+
+
+@Category({MasterTests.class, MediumTests.class})
+public class TestModifyTableWhileMerging {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+      HBaseClassTestRule.forClass(TestModifyTableWhileMerging.class);
+
+  private static final Logger LOG = LoggerFactory
+      .getLogger(TestModifyTableWhileMerging.class);
+
+  protected static final HBaseTestingUtility UTIL = new HBaseTestingUtility();
+  private static TableName TABLE_NAME = TableName.valueOf("test");
+  private static Admin admin;
+  private static Table client;
+  private static byte[] CF = Bytes.toBytes("cf");
+  private static byte[] SPLITKEY = Bytes.toBytes("bbbbbbb");
+
+  @BeforeClass
+  public static void setupCluster() throws Exception {
+    //Set procedure executor thread to 1, making reproducing this issue of HBASE-20921 easier
+    UTIL.getConfiguration().setInt(MasterProcedureConstants.MASTER_PROCEDURE_THREADS, 1);
+    UTIL.startMiniCluster(1);
+    admin = UTIL.getHBaseAdmin();
+    byte[][] splitKeys = new byte[1][];
+    splitKeys[0] = SPLITKEY;
+    client = UTIL.createTable(TABLE_NAME, CF, splitKeys);
+    UTIL.waitTableAvailable(TABLE_NAME);
+  }
+
+  @AfterClass
+  public static void cleanupTest() throws Exception {
+    try {
+      UTIL.shutdownMiniCluster();
+    } catch (Exception e) {
+      LOG.warn("failure shutting down cluster", e);
+    }
+  }
+
+  @Test
+  public void test() throws Exception {
+    TableDescriptor tableDescriptor = client.getDescriptor();
+    ProcedureExecutor<MasterProcedureEnv> executor = UTIL.getMiniHBaseCluster().getMaster()
+        .getMasterProcedureExecutor();
+    MasterProcedureEnv env = executor.getEnvironment();
+    List<RegionInfo> regionInfos = admin.getRegions(TABLE_NAME);
+    MergeTableRegionsProcedure mergeTableRegionsProcedure = new MergeTableRegionsProcedure(
+      UTIL.getMiniHBaseCluster().getMaster().getMasterProcedureExecutor()
+        .getEnvironment(), regionInfos.get(0), regionInfos.get(1));
+    ModifyTableProcedure modifyTableProcedure = new ModifyTableProcedure(env, tableDescriptor);
+    long procModify = executor.submitProcedure(modifyTableProcedure);
+    UTIL.waitFor(30000, () -> executor.getProcedures().stream()
+      .filter(p -> p instanceof ModifyTableProcedure)
+      .map(p -> (ModifyTableProcedure) p)
+      .anyMatch(p -> TABLE_NAME.equals(p.getTableName())));
+    long proc = executor.submitProcedure(mergeTableRegionsProcedure);
+    UTIL.waitFor(3000000, () -> UTIL.getMiniHBaseCluster().getMaster()
+        .getMasterProcedureExecutor().isFinished(procModify));
+    Assert.assertEquals("Modify Table procedure should success!",
+        ProcedureProtos.ProcedureState.SUCCESS, modifyTableProcedure.getState());
+  }
+
+}