Task pre-emption disable is broken due to pseudo ISR tasks

[Sebastian Huber]

We have for example:

Scheduler_Void_or_thread _Scheduler_priority_Unblock (
  const Scheduler_Control *scheduler,
  Thread_Control          *the_thread
)
{
  Scheduler_priority_Context *context =
    _Scheduler_priority_Get_context( scheduler );
  Scheduler_priority_Node *node = _Scheduler_priority_Thread_get_node( the_thread );

  _Scheduler_priority_Ready_queue_enqueue(
    &the_thread->Object.Node,
    &node->Ready_queue,
    &context->Bit_map
  );

  /* TODO: flash critical section? */

  /*
   *  If the thread that was unblocked is more important than the heir,
   *  then we have a new heir.  This may or may not result in a
   *  context switch.
   *
   *  Normal case:
   *    If the current thread is preemptible, then we need to do
   *    a context switch.
   *  Pseudo-ISR case:
   *    Even if the thread isn't preemptible, if the new heir is
   *    a pseudo-ISR system task, we need to do a context switch.
   */
  if ( the_thread->current_priority < _Thread_Heir->current_priority ) {
    _Scheduler_Update_heir(
      the_thread,
      the_thread->current_priority == PRIORITY_PSEUDO_ISR
    );
  }

  SCHEDULER_RETURN_VOID_OR_NULL;
}

So the unblock event of a pseudo ISR task (MPCI or timer server) may pre-empt a task with disabled pre-emption. Suppose a higher priority task than the non-preemptible task is ready. Then this task gets scheduled once the pseudo ISR task blocks again.

[Sebastian Huber <sebastian.huber@…>]

In 0562060f074eea3fdcf5274aa3b7cbc8fe14993d/rtems:

sptests/sptasknopreempt01: New test

Update #2365.

[Sebastian Huber <sebastian.huber@…>]

In f1eb94b/rtems-docs:

c-user: Do not mention pseudo-interrupt priority

Update #2365.

[Sebastian Huber <sebastian.huber@…>]

In 7fe6d60/rtems:

score: Remove PRIORITY_PSEUDO_ISR thread priority

The uniprocessor schedulers had some special case logic for the
PRIORITY_PSEUDO_ISR priority. Tasks with a priority of PRIORITY_PSEUDO_ISR
were allowed to preempt a not preemptible task. If other higher priority task
are made ready while a PRIORITY_PSEUDO_ISR task preempts a not preemptible
task, then the other tasks run before the not preemptible task. This made the
RTEMS_NO_PREEMPT mode ineffective.

Remove the PRIORITY_PSEUDO_ISR special case logic. This simplifies the
uniprocessor schedulers. Move the uniprocessor-specific scheduler support to
the new header file <rtems/score/scheduleruniimpl.h>.

Close #2365.