HBASE-30142 Resolve NPE while running recoverUnknown command because null RegionLocation

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

@@ -980,11 +980,14 @@ public synchronized boolean isServerDead(ServerName serverName) {
   /**
    * Check if a server is unknown. A server can be online, or known to be dead, or unknown to this
    * manager (i.e, not online, not known to be dead either; it is simply not tracked by the master
-   * any more, for example, a very old previous instance).
+   * any more, for example, a very old previous instance). A null serverName should not be
+   * considered unknown. We set regionLocation null before finding the assign candidate (in-between
+   * region transition) or while marking it OFFLINE/FAILED_OPEN For more info regarding null-check
+   * in this refer HBASE-30142
    */
   public boolean isServerUnknown(ServerName serverName) {
-    return serverName == null
-      || (!onlineServers.containsKey(serverName) && !deadservers.isDeadServer(serverName));
+    return serverName != null
+      && (!onlineServers.containsKey(serverName) && !deadservers.isDeadServer(serverName));
   }
 
   public void shutdownCluster() {

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

@@ -0,0 +1,112 @@
+/*
+ * 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;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.List;
+import org.apache.hadoop.hbase.HBaseTestingUtil;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.client.RegionInfo;
+import org.apache.hadoop.hbase.client.Table;
+import org.apache.hadoop.hbase.master.assignment.AssignmentManager;
+import org.apache.hadoop.hbase.master.assignment.RegionStateNode;
+import org.apache.hadoop.hbase.testclassification.MasterTests;
+import org.apache.hadoop.hbase.testclassification.MediumTests;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+import org.apache.hadoop.hbase.shaded.protobuf.generated.MasterProtos;
+
+/**
+ * Test for HBASE-30142. Verifies that {@code scheduleSCPsForUnknownServers} (i.e. the
+ * recoverUnknown HBCK command) does not throw a NullPointerException when a region's
+ * {@code regionLocation} is null while its state is something other than OFFLINE.
+ * <p/>
+ * Before HBASE-30142, {@link ServerManager#isServerUnknown(org.apache.hadoop.hbase.ServerName)}
+ * returned {@code true} for a {@code null} server name, so a region whose location had been
+ * temporarily nulled (e.g. between region transitions or while marking it FAILED_OPEN /
+ * ABNORMALLY_CLOSED) was treated as living on an "unknown" server. The downstream call to
+ * {@code shouldSubmitSCP(null)} then dereferenced the null and crashed.
+ */
+@Tag(MasterTests.TAG)
+@Tag(MediumTests.TAG)
+public class TestRecoverUnknownWithNullRegionLocation {
+
+  private static HBaseTestingUtil UTIL;
+  private static final TableName TABLE_NAME =
+    TableName.valueOf("TestRecoverUnknownWithNullRegionLocation");
+  private static final byte[] FAMILY = Bytes.toBytes("cf");
+
+  @BeforeAll
+  public static void setUpBeforeClass() throws Exception {
+    UTIL = new HBaseTestingUtil();
+    UTIL.startMiniCluster(2);
+  }
+
+  @AfterAll
+  public static void tearDownAfterClass() throws Exception {
+    if (UTIL != null) {
+      UTIL.shutdownMiniCluster();
+    }
+  }
+
+  /**
+   * Drive the region into ABNORMALLY_CLOSED through the
+   * {@link AssignmentManager#regionClosedAbnormally(RegionStateNode)} path (the same path SCP
+   * uses). That method also nulls {@code regionLocation} while leaving state non-OFFLINE. Then call
+   * {@code scheduleSCPsForUnknownServers} and assert no NPE.
+   */
+  @Test
+  public void testRecoverUnknownWithAbnormallyClosedRegion() throws Exception {
+    try (Table ignored = UTIL.createTable(TABLE_NAME, FAMILY)) {
+      UTIL.waitTableAvailable(TABLE_NAME);
+
+      HMaster master = UTIL.getMiniHBaseCluster().getMaster();
+      AssignmentManager am = master.getAssignmentManager();
+      List<RegionInfo> regions = am.getTableRegions(TABLE_NAME, true);
+      assertFalse(regions.isEmpty(), "expected at least one region");
+      RegionStateNode node = am.getRegionStates().getRegionStateNode(regions.get(0));
+      assertNotNull(node, "expected a region state node for the test region");
+
+      node.lock();
+      try {
+        am.regionClosedAbnormally(node).get();
+      } finally {
+        node.unlock();
+      }
+
+      assertTrue(node.isInState(RegionState.State.ABNORMALLY_CLOSED),
+        "regionClosedAbnormally must move state to ABNORMALLY_CLOSED");
+      assertNull(node.getRegionLocation(), "regionClosedAbnormally must null out the location");
+
+      MasterProtos.ScheduleSCPsForUnknownServersResponse response =
+        master.getMasterRpcServices().scheduleSCPsForUnknownServers(null,
+          MasterProtos.ScheduleSCPsForUnknownServersRequest.newBuilder().build());
+      assertEquals(0, response.getPidCount(),
+        "no SCPs should be scheduled for an ABNORMALLY_CLOSED region with null location");
+    }
+  }
+}