The mbuf_queue API allows read access to integer variables which

The mbuf_queue API allows read access to integer variables which
another CPU may change simultaneously.  To prevent miss optimisation
by the compiler, they need the READ_ONCE() macro.  Otherwise there
could be two read operations with inconsistent values.  Writing to
integer in mq_set_maxlen() needs mutex protection.  Otherwise the
value could change within critical sections.  Again the compiler
could optimize to multiple read operations within the critical
section.  With inconsistent values, the behavior is undefined.
OK dlg@