score: Update _Thread_Heir only if necessary

Previously, the _Thread_Heir was updated unconditionally in case a new
heir was determined.  The _Thread_Dispatch_necessary was only updated in
case the executing thread was preemptible or an internal thread was
unblocked.  Change this to update the _Thread_Heir and
_Thread_Dispatch_necessary only in case the currently selected heir
thread is preemptible or a dispatch is forced.  Move the schedule
decision into the change priority operation and use the schedule
operation only in rtems_task_mode() in case preemption is enabled or an
ASR dispatch is necessary.  This is a behaviour change.  Previously, the
RTEMS_NO_PREEMPT also prevented signal delivery in certain cases (not
always).  Now, signal delivery is no longer influenced by
RTEMS_NO_PREEMPT.  Since the currently selected heir thread is used to
determine if a new heir is chosen, non-preemptible heir threads
currently not executing now prevent a new heir.  This may have an
application impact, see change test tm04.  Document this change in sp04.

Update #2273.

1 files changed, 1 insertions, 8 deletions

diff --git a/cpukit/score/src/threadchangepriority.c b/cpukit/score/src/threadchangepriority.c
index ca2c5871af..d61dfb859a 100644
--- a/cpukit/score/src/threadchangepriority.c
+++ b/cpukit/score/src/threadchangepriority.c
@@ -46,17 +46,10 @@ void _Thread_Change_priority(
         new_priority,
         prepend_it
       );
-
-      _ISR_Flash( level );
-
-      /*
-       *  We altered the set of thread priorities.  So let's figure out
-       *  who is the heir and if we need to switch to them.
-       */
-      _Scheduler_Schedule( the_thread );
     } else {
       _Scheduler_Update_priority( the_thread, new_priority );
     }
+
     _ISR_Enable( level );
 
     _Thread_queue_Requeue( the_thread->Wait.queue, the_thread );