Bug #19938 Valgrind error (race) in handle_slave_sql()

sql/slave.cc:
  Read rli->events_till_abort to a temporary variable before unlocking the mutex

sql/slave.cc

@@ -3949,10 +3949,17 @@ the slave SQL thread with \"SLAVE START\". We stopped at log \
   delete thd;
   pthread_mutex_unlock(&LOCK_thread_count);
   pthread_cond_broadcast(&rli->stop_cond);
+
+  /*
+    Bug #19938 Valgrind error (race) in handle_slave_sql()
+    Read the value of rli->event_till_abort before releasing the mutex
+  */
+  const int eta= rli->events_till_abort;
+
   // tell the world we are done
   pthread_mutex_unlock(&rli->run_lock);
 #ifndef DBUG_OFF // TODO: reconsider the code below
-  if (abort_slave_event_count && !rli->events_till_abort)
+  if (abort_slave_event_count && !eta)
     goto slave_begin;
 #endif  
   my_thread_end();