PXC optimizations

[midenok]

@@ -1814,15 +1863,21 @@ log_online_purge_changed_page_bitmaps(
                lsn = LSN_MAX;
        }
 
+       bool log_bmp_sys_inited = false;
        if (srv_redo_log_thread_started) {
                /* User requests might happen with both enabled and disabled
                tracking */
-               mutex_enter(&log_bmp_sys->mutex);
+               log_bmp_sys_inited = true;
+               mutex_enter(&log_bmp_sys_mutex);
+               if (!srv_redo_log_thread_started) {
+                       log_bmp_sys_inited = false;
+                       mutex_exit(&log_bmp_sys_mutex);
+               }
        }
 
        if (!log_online_setup_bitmap_file_range(&bitmap_files, 0, LSN_MAX)) {
-               if (srv_redo_log_thread_started) {
-                       mutex_exit(&log_bmp_sys->mutex);
+               if (log_bmp_sys_inited) {
+                       mutex_exit(&log_bmp_sys_mutex);
                }
                return true;
        }

Commit c01c75da8ec67197e5b2f86edbdd9541df717faa