Changeset b8a5abf in rtems for cpukit/score/src/schedulercbsunblock.c

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.