diff --git a/core/includes/cache.inc b/core/includes/cache.inc
index 89506a0..06b0ab1 100644
--- a/core/includes/cache.inc
+++ b/core/includes/cache.inc
@@ -53,17 +53,7 @@ function cache($bin = 'cache') {
  *   The list of tags to invalidate cache items for.
  */
 function cache_invalidate(array $tags) {
-  foreach (cache_get_backends() as $bin => $class) {
+  foreach (CacheFactory::getBackends() as $bin => $class) {
     cache($bin)->invalidateTags($tags);
   }
 }
-
-/**
- * Returns a list of cache backends for this site.
- *
- * @return
- *   An associative array with cache bins as keys, and backend classes as value.
- */
-function cache_get_backends() {
-  return variable_get('cache_classes', array('cache' => 'Drupal\Core\Cache\DatabaseBackend'));
-}
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 09b3e86..94b1c4a 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -280,9 +280,13 @@ function install_begin_request(&$install_state) {
   // If it is not, replace the configuration storage with the InstallStorage
   // implementation, for the following reasons:
   // - The first call into drupal_container() will try to set up the regular
-  //   runtime configuration storage, using the CachedStorage. The storage
-  //   controller requires to pass in the active config directory name, but that
-  //   directory does not exist yet.
+  //   runtime configuration storage, using the CachedStorage by default. It
+  //   calls config_get_config_directory() to retrieve the config directory to
+  //   use, but that throws an exception, since $config_directories is not
+  //   defined since there is no settings.php yet. If there is a prepared
+  //   settings.php already, then the returned directory still cannot be used,
+  //   because it does not necessarily exist. The installer ensures that it
+  //   exists and is writeable in a later step.
   // - The installer outputs maintenance theme pages and performs many other
   //   operations, which try to load configuration. Since there is no active
   //   configuration yet, and because the configuration system does not have a
diff --git a/core/lib/Drupal/Core/Cache/CacheFactory.php b/core/lib/Drupal/Core/Cache/CacheFactory.php
index fdbaeb7..da42a26 100644
--- a/core/lib/Drupal/Core/Cache/CacheFactory.php
+++ b/core/lib/Drupal/Core/Cache/CacheFactory.php
@@ -27,22 +27,30 @@ class CacheFactory {
    * @return Drupal\Core\Cache\CacheBackendInterface
    *   The cache backend object associated with the specified bin.
    */
-  static function get($bin) {
+  public static function get($bin) {
+    // Check whether there is a custom class defined for the requested bin or
+    // use the default 'cache' definition otherwise.
+    $cache_backends = self::getBackends();
+    $class = isset($cache_backends[$bin]) ? $cache_backends[$bin] : $cache_backends['cache'];
+    return new $class($bin);
+  }
+
+  /**
+   * Returns a list of cache backends for this site.
+   *
+   * @return array
+   *   An associative array with cache bins as keys, and backend class names as
+   *   value.
+   */
+  public static function getBackends() {
     // @todo Improve how cache backend classes are defined. Cannot be
     //   configuration, since e.g. the CachedStorage config storage controller
     //   requires the definition in its constructor already.
     global $conf;
     $cache_backends = isset($conf['cache_classes']) ? $conf['cache_classes'] : array();
-
-    // Check whether there is a custom class defined for the requested bin and
-    // default to the DatabaseBackend otherwise.
-    if (isset($cache_backends[$bin])) {
-      $class = $cache_backends[$bin];
-    }
-    else {
-      $class = 'Drupal\Core\Cache\DatabaseBackend';
-    }
-    return new $class($bin);
+    // Ensure there is a default 'cache' bin definition.
+    $cache_backends += array('cache' => 'Drupal\Core\Cache\DatabaseBackend');
+    return $cache_backends;
   }
 
 }
diff --git a/core/lib/Drupal/Core/Config/CachedStorage.php b/core/lib/Drupal/Core/Config/CachedStorage.php
index e17f56f..2278bf9 100644
--- a/core/lib/Drupal/Core/Config/CachedStorage.php
+++ b/core/lib/Drupal/Core/Config/CachedStorage.php
@@ -49,8 +49,9 @@ public function __construct(StorageInterface $storage, CacheBackendInterface $ca
    * Implements Drupal\Core\Config\StorageInterface::exists().
    */
   public function exists($name) {
-    // A single storage lookup is faster than a cache lookup and possibly
-    // subsequent storage lookup.
+    // The cache would read in the entire data (instead of only checking whether
+    // any data exists), and on a potential cache miss, an additional storage
+    // lookup would have to happen, so check the storage directly.
     return $this->storage->exists($name);
   }
 
@@ -70,6 +71,11 @@ public function read($name) {
     if ($data !== FALSE) {
       $this->cache->set($name, $data, CacheBackendInterface::CACHE_PERMANENT, array('config' => array($name)));
     }
+    // If the cache contained bogus data and there is no data in the storage,
+    // wipe the cache entry.
+    elseif ($cache) {
+      $this->cache->delete($name);
+    }
     return $data;
   }
 
@@ -77,6 +83,8 @@ public function read($name) {
    * Implements Drupal\Core\Config\StorageInterface::write().
    */
   public function write($name, array $data) {
+    // Not all data that is written is necessarily read; just invalidate the
+    // cache.
     $this->cache->delete($name);
     return $this->storage->write($name, $data);
   }
@@ -101,14 +109,14 @@ public function rename($name, $new_name) {
   /**
    * Implements Drupal\Core\Config\StorageInterface::encode().
    */
-  public static function encode($data) {
+  public function encode($data) {
     return $this->storage->encode($data);
   }
 
   /**
    * Implements Drupal\Core\Config\StorageInterface::decode().
    */
-  public static function decode($raw) {
+  public function decode($raw) {
     return $this->storage->decode($raw);
   }
 
diff --git a/core/lib/Drupal/Core/Config/DatabaseStorage.php b/core/lib/Drupal/Core/Config/DatabaseStorage.php
index 43c8168..1fb87b0 100644
--- a/core/lib/Drupal/Core/Config/DatabaseStorage.php
+++ b/core/lib/Drupal/Core/Config/DatabaseStorage.php
@@ -57,7 +57,7 @@ public function __construct(Connection $connection, $table, array $options = arr
    * Implements Drupal\Core\Config\StorageInterface::exists().
    */
   public function exists($name) {
-    return (bool) $this->connection->queryRange('SELECT 1 FROM {' . $this->table . '} WHERE name = :name', 0, 1, array(
+    return (bool) $this->connection->queryRange('SELECT 1 FROM {' . $this->connection->escapeTable($this->table) . '} WHERE name = :name', 0, 1, array(
       ':name' => $name,
     ), $this->options)->fetchField();
   }
@@ -76,7 +76,7 @@ public function read($name) {
     // catch the exception and just return an empty array so the caller can
     // handle it if need be.
     try {
-      $raw = $this->connection->query('SELECT data FROM {' . $this->table . '} WHERE name = :name', array(':name' => $name), $this->options)->fetchField();
+      $raw = $this->connection->query('SELECT data FROM {' . $this->connection->escapeTable($this->table) . '} WHERE name = :name', array(':name' => $name), $this->options)->fetchField();
       if ($raw !== FALSE) {
         $data = $this->decode($raw);
       }
@@ -156,7 +156,7 @@ public function decode($raw) {
    *   Only thrown in case $this->options['throw_exception'] is TRUE.
    */
   public function listAll($prefix = '') {
-    return $this->connection->query('SELECT name FROM {' . $this->table . '} WHERE name LIKE :name', array(
+    return $this->connection->query('SELECT name FROM {' . $this->connection->escapeTable($this->table) . '} WHERE name LIKE :name', array(
       ':name' => db_like($prefix) . '%',
     ), $this->options)->fetchCol();
   }
diff --git a/core/modules/search/lib/Drupal/search/Tests/SearchExcerptTest.php b/core/modules/search/lib/Drupal/search/Tests/SearchExcerptTest.php
index 99fd422..d97975b 100644
--- a/core/modules/search/lib/Drupal/search/Tests/SearchExcerptTest.php
+++ b/core/modules/search/lib/Drupal/search/Tests/SearchExcerptTest.php
@@ -13,6 +13,12 @@
  * Tests the search_excerpt() function.
  */
 class SearchExcerptTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
   public static $modules = array('search');
 
   public static function getInfo() {