--- a/src/share/classes/java/util/HashMap.java	Fri Jun 22 19:10:19 2018 +0100
+++ b/src/share/classes/java/util/HashMap.java	Fri Jun 15 12:00:45 2018 +0530
@@ -491,7 +491,7 @@
     }
 
     /**
-     * Implements Map.putAll and Map constructor
+     * Implements Map.putAll and Map constructor.
      *
      * @param m the map
      * @param evict false when initially constructing this map, else
@@ -558,7 +558,7 @@
     }
 
     /**
-     * Implements Map.get and related methods
+     * Implements Map.get and related methods.
      *
      * @param hash hash for key
      * @param key the key
@@ -613,7 +613,7 @@
     }
 
     /**
-     * Implements Map.put and related methods
+     * Implements Map.put and related methods.
      *
      * @param hash hash for key
      * @param key the key
@@ -701,7 +701,7 @@
         }
         threshold = newThr;
         @SuppressWarnings({"rawtypes","unchecked"})
-            Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
+        Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
         table = newTab;
         if (oldTab != null) {
             for (int j = 0; j < oldCap; ++j) {
@@ -801,7 +801,7 @@
     }
 
     /**
-     * Implements Map.remove and related methods
+     * Implements Map.remove and related methods.
      *
      * @param hash hash for key
      * @param key the key
@@ -1364,8 +1364,11 @@
     }
 
     /**
-     * Reconstitute the {@code HashMap} instance from a stream (i.e.,
-     * deserialize it).
+     * Reconstitutes this map from a stream (that is, deserializes it).
+     * @param s the stream
+     * @throws ClassNotFoundException if the class of a serialized object
+     *         could not be found
+     * @throws IOException if an I/O error occurs
      */
     private void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException {
@@ -1905,7 +1908,6 @@
 
         /**
          * Forms tree of the nodes linked from this node.
-         * @return root of tree
          */
         final void treeify(Node<K,V>[] tab) {
             TreeNode<K,V> root = null;
@@ -2043,8 +2045,11 @@
                 return;
             if (root.parent != null)
                 root = root.root();
-            if (root == null || root.right == null ||
-                (rl = root.left) == null || rl.left == null) {
+            if (root == null
+                || (movable
+                    && (root.right == null
+                        || (rl = root.left) == null
+                        || rl.left == null))) {
                 tab[index] = first.untreeify(map);  // too small
                 return;
             }
@@ -2273,7 +2278,7 @@
 
         static <K,V> TreeNode<K,V> balanceDeletion(TreeNode<K,V> root,
                                                    TreeNode<K,V> x) {
-            for (TreeNode<K,V> xp, xpl, xpr;;)  {
+            for (TreeNode<K,V> xp, xpl, xpr;;) {
                 if (x == null || x == root)
                     return root;
                 else if ((xp = x.parent) == null) {

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/java/util/HashMap/Bug8186171Test.java	Fri Jun 15 12:00:45 2018 +0530
@@ -0,0 +1,157 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+import java.util.List;
+import java.util.Map;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.ArrayList;
+import java.util.concurrent.ThreadLocalRandom;
+
+import org.testng.annotations.Test;
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertFalse;
+import static org.testng.Assert.assertTrue;
+
+/*
+ * @test
+ * @bug 8186171
+ * @run testng Bug8186171Test
+ * @summary Verify the fix for scenario reported in JDK-8186171
+ * @author deepak.kejriwal@oracle.com
+ */
+@Test
+public class Bug8186171Test{
+
+    /**
+     * Tests and extends the scenario reported in
+     * https://bugs.openjdk.java.net/browse/JDK-8186171
+     * HashMap: Entry.setValue may not work after Iterator.remove() called for previous entries
+     * Runs 1000 times as it is based on randomization.
+     */
+    @Test(invocationCount = 1000)
+    static void testBug8186171NonDeterministic()
+    {
+        final ThreadLocalRandom rnd = ThreadLocalRandom.current();
+
+        final Object v1 = rnd.nextBoolean() ? null : 1;
+        final Object v2 = (rnd.nextBoolean() && v1 != null) ? null : 2;
+
+        /** If true, always lands in first bucket in hash tables. */
+        final boolean poorHash = rnd.nextBoolean();
+
+        class Key implements Comparable<Key> {
+            final int i;
+            Key(int i) { this.i = i; }
+            public int hashCode() { return poorHash ? 0 : super.hashCode(); }
+            public int compareTo(Key x) {
+                return Integer.compare(this.i, x.i);
+            }
+        }
+
+        // HashMap and ConcurrentHashMap have:
+        // TREEIFY_THRESHOLD = 8; UNTREEIFY_THRESHOLD = 6;
+        final int size = rnd.nextInt(1, 25);
+
+        List<Key> keys = new ArrayList<>();
+        for (int i = size; i-->0; ) keys.add(new Key(i));
+        Key keyToFrob = keys.get(rnd.nextInt(keys.size()));
+
+        Map<Key, Object> m = new HashMap<Key, Object>();
+
+        for (Key key : keys) m.put(key, v1);
+
+        for (Iterator<Map.Entry<Key, Object>> it = m.entrySet().iterator();
+             it.hasNext(); ) {
+            Map.Entry<Key, Object> entry = it.next();
+            if (entry.getKey() == keyToFrob)
+                entry.setValue(v2); // does this have the expected effect?
+            else
+                it.remove();
+        }
+
+        assertFalse(m.containsValue(v1));
+        assertTrue(m.containsValue(v2));
+        assertTrue(m.containsKey(keyToFrob));
+        assertEquals(1, m.size());
+    }
+
+
+    /**
+     * Tests and extends the scenario reported in
+     * https://bugs.openjdk.java.net/browse/JDK-8186171
+     * HashMap: Entry.setValue may not work after Iterator.remove() called for previous entries
+     * Runs single time by reproducing exact scenario for issue mentioned in 8186171
+     */
+    @Test()
+    static void testBug8186171Deterministic(){
+        class Key implements Comparable<Key>
+        {
+            final int i;
+            Key(int i) { this.i = i; }
+
+            @Override
+            public int hashCode() { return 0; } //Returning same hashcode so that all keys landup to same bucket
+
+            @Override
+            public int compareTo(Key x){
+                if(this.i == x.i){
+                    return 0;
+                }
+                else {
+                    return Integer.compare(this.i, x.i);
+                }
+            }
+            @Override
+            public String toString()
+            {
+                return "Key_" + i;
+            }
+        }
+
+        // HashMap have TREEIFY_THRESHOLD = 8; UNTREEIFY_THRESHOLD = 6;
+        final int size = 11;
+        List<Key> keys = new ArrayList<>();
+
+        for (int i = 0; i < size; i++){
+            keys.add(new Key(i));
+        }
+
+        Key keyToFrob = keys.get(9);
+        Map<Key, Object> m = new HashMap<Key, Object>();
+        for (Key key : keys) m.put(key, null);
+
+        for (Iterator<Map.Entry<Key, Object>> it = m.entrySet().iterator(); it.hasNext(); ){
+            Map.Entry<Key, Object> entry = it.next();
+            if (entry.getKey() == keyToFrob){
+                entry.setValue(2);
+            }
+            else{
+                it.remove();
+            }
+        }
+
+        assertFalse(m.containsValue(null));
+        assertTrue(m.containsValue(2));
+        assertTrue(m.containsKey(keyToFrob));
+        assertEquals(1, m.size());
+    }
+}