diff --git a/core/java/com/android/internal/widget/ILockSettingsObserver.aidl b/core/java/com/android/internal/widget/ILockSettingsObserver.aidl
index 6c354d8..edf8f0e 100644
--- a/core/java/com/android/internal/widget/ILockSettingsObserver.aidl
+++ b/core/java/com/android/internal/widget/ILockSettingsObserver.aidl
@@ -18,5 +18,14 @@
 
 /** {@hide} */
 oneway interface ILockSettingsObserver {
+    /**
+     * Called when a lock setting has changed.
+     *
+     * Note: Impementations of this should do as little work as possible, because this may be
+     * called synchronously while writing a setting.
+     *
+     * @param key the key of the setting that has changed or {@code null} if any may have changed.
+     * @param userId the user whose setting has changed.
+     */
     void onLockSettingChanged(in String key, in int userId);
 }
diff --git a/core/java/com/android/internal/widget/LockPatternUtils.java b/core/java/com/android/internal/widget/LockPatternUtils.java
index d6885da..a4b8380 100644
--- a/core/java/com/android/internal/widget/LockPatternUtils.java
+++ b/core/java/com/android/internal/widget/LockPatternUtils.java
@@ -65,6 +65,13 @@
     private static final boolean DEBUG = false;
 
     /**
+     * If true, LockPatternUtils will cache its values in-process. While this leads to faster reads,
+     * it can cause problems because writes to to the settings are no longer synchronous
+     * across all processes.
+     */
+    private static final boolean ENABLE_CLIENT_CACHE = false;
+
+    /**
      * The maximum number of incorrect attempts before the user is prevented
      * from trying again for {@link #FAILED_ATTEMPT_TIMEOUT_MS}.
      */
@@ -207,8 +214,13 @@
 
     private ILockSettings getLockSettings() {
         if (mLockSettingsService == null) {
-            mLockSettingsService = LockPatternUtilsCache.getInstance(
-                    ILockSettings.Stub.asInterface(ServiceManager.getService("lock_settings")));
+            ILockSettings service = ILockSettings.Stub.asInterface(
+                    ServiceManager.getService("lock_settings"));
+            if (ENABLE_CLIENT_CACHE) {
+                mLockSettingsService = LockPatternUtilsCache.getInstance(service);
+            } else {
+                mLockSettingsService = service;
+            }
         }
         return mLockSettingsService;
     }
diff --git a/core/java/com/android/internal/widget/LockPatternUtilsCache.java b/core/java/com/android/internal/widget/LockPatternUtilsCache.java
index 624f67c..a9524ff 100644
--- a/core/java/com/android/internal/widget/LockPatternUtilsCache.java
+++ b/core/java/com/android/internal/widget/LockPatternUtilsCache.java
@@ -18,7 +18,9 @@
 
 import android.os.IBinder;
 import android.os.RemoteException;
+import android.os.UserHandle;
 import android.util.ArrayMap;
+import android.util.Log;
 
 /**
  * A decorator for {@link ILockSettings} that caches the key-value responses in memory.
@@ -28,9 +30,11 @@
  */
 public class LockPatternUtilsCache implements ILockSettings {
 
-    private static final String HAS_LOCK_PATTERN_CACHE_KEY
+    private static final String TAG = "LockPatternUtilsCache";
+
+    public static final String HAS_LOCK_PATTERN_CACHE_KEY
             = "LockPatternUtils.Cache.HasLockPatternCacheKey";
-    private static final String HAS_LOCK_PASSWORD_CACHE_KEY
+    public static final String HAS_LOCK_PASSWORD_CACHE_KEY
             = "LockPatternUtils.Cache.HasLockPasswordCacheKey";
 
     private static LockPatternUtilsCache sInstance;
@@ -53,7 +57,7 @@
 
     // ILockSettings
 
-    private LockPatternUtilsCache(ILockSettings service) {
+    public LockPatternUtilsCache(ILockSettings service) {
         mService = service;
         try {
             service.registerObserver(mObserver);
@@ -186,6 +190,7 @@
     // Caching
 
     private Object peekCache(String key, int userId) {
+        if (!validateUserId(userId)) return null;
         synchronized (mCache) {
             // Safe to reuse mCacheKey, because it is not stored in the map.
             return mCache.get(mCacheKey.set(key, userId));
@@ -193,6 +198,7 @@
     }
 
     private void putCache(String key, int userId, Object value) {
+        if (!validateUserId(userId)) return;
         synchronized (mCache) {
             // Create a new key, because this will be stored in the map.
             mCache.put(new CacheKey().set(key, userId), value);
@@ -200,9 +206,14 @@
     }
 
     private void invalidateCache(String key, int userId) {
+        if (!validateUserId(userId)) return;
         synchronized (mCache) {
-            // Safe to reuse mCacheKey, because it is not stored in the map.
-            mCache.remove(mCacheKey.set(key, userId));
+            if (key != null) {
+                // Safe to reuse mCacheKey, because it is not stored in the map.
+                mCache.remove(mCacheKey.set(key, userId));
+            } else {
+                mCache.clear();
+            }
         }
     }
 
@@ -213,6 +224,14 @@
         }
     };
 
+    private final boolean validateUserId(int userId) {
+        if (userId < UserHandle.USER_OWNER) {
+            Log.e(TAG, "User " + userId + " not supported: Must be a concrete user.");
+            return false;
+        }
+        return true;
+    }
+
     private static final class CacheKey {
         String key;
         int userId;
diff --git a/services/core/java/com/android/server/LockSettingsService.java b/services/core/java/com/android/server/LockSettingsService.java
index 11ba8e8..3c7d85d 100644
--- a/services/core/java/com/android/server/LockSettingsService.java
+++ b/services/core/java/com/android/server/LockSettingsService.java
@@ -49,6 +49,7 @@
 import com.android.internal.widget.ILockSettings;
 import com.android.internal.widget.ILockSettingsObserver;
 import com.android.internal.widget.LockPatternUtils;
+import com.android.internal.widget.LockPatternUtilsCache;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -348,6 +349,7 @@
         final byte[] hash = LockPatternUtils.patternToHash(
                 LockPatternUtils.stringToPattern(pattern));
         mStorage.writePatternHash(hash, userId);
+        notifyObservers(LockPatternUtilsCache.HAS_LOCK_PATTERN_CACHE_KEY, userId);
     }
 
     @Override
@@ -357,6 +359,7 @@
         maybeUpdateKeystore(password, userId);
 
         mStorage.writePasswordHash(mLockPatternUtils.passwordToHash(password, userId), userId);
+        notifyObservers(LockPatternUtilsCache.HAS_LOCK_PASSWORD_CACHE_KEY, userId);
     }
 
     @Override