[RTEMS Project] #4804: broadcasting message to single task with higher importance priority can generate multiple messages

[RTEMS trac]

#4804: broadcasting message to single task with higher importance priority can
generate multiple messages
---------------------------------+--------------------
  Reporter:  Martin Erik Werner  |      Owner:  (none)
      Type:  defect              |     Status:  new
  Priority:  normal              |  Milestone:
 Component:  score               |    Version:  4.11
  Severity:  normal              |   Keywords:
Blocked By:                      |   Blocking:
---------------------------------+--------------------
 When a task with lower importance priority broadcasts a single message via
 a message queue to a task with higher importance priority, it can cause
 multiple messages to be received.

 This seems to occur if the broadcasting task is completely blocked while
 the receiving task performs multiple receives.

 A speculative guess would be that the broadcasting task ends up in a loop
 where it copies the message and unblocks tasks, but does not keep track of
 which tasks it has sent to? Thus, if a receiving task is unblocked with
 the message and then returns to waiting on the message queue again without
 the broadcasting task being allowed to exit the loop, the receiving task
 will be unblocked with the same message again.

 I have attached the source code of a minimal-ish application which has
 been able to reproduce this issue on RTEMS 4.11 running on leon3 hardware.

 (I had a quick look through Git and could not see any changes to the
 broadcast code between 4.11 and the latest master that seemed directly
 related, so possibly the behaviour is still present.)

 In this application, the potential amount of messages received from a
 single broadcast to a single task is seemingly infinite (the application
 stops it after an arbitrary set limit of 12345 messages).

 Enabling the following section makes the behaviour disappear and only 1
 message is received.
 {{{
 #!c
 #if 0
     /* If unblocking broadcaster, multiple messages are no longer
 received. */
     status = rtems_task_wake_after(1);
     assert(status == RTEMS_SUCCESSFUL);
 #endif
 }}}

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Ticket URL: <http://devel.rtems.org/ticket/4804>
RTEMS Project <http://www.rtems.org/>
RTEMS Project