in file buf0mtflu.cc line 439

  Analysis: At shutdown multi-threaded flush sends a exit work
  items to all mtflush threads. We wait until the work queue is
  empty. However, as we did not hold the mutex, some other thread
  could also put work-items to work queue.

  Fix: Take mutex before adding exit work items to work queue and
  wait until all work-items are really processed. Release
  mutex after we have marked that multi-threaded flush is not
  anymore active.

  Fix test failure on innodb_bug12902967 caused by unnecessary
  info output on xtradb/buf/buf0mtflush.cc.

   Do not try to enable atomic writes if the file type
   is not OS_DATA_FILE. Atomic writes are unnecessary
   for log files. If we try to enable atomic writes
   to log writes that are stored to media supporting
   atomic writes we will end up problems later.