Re-implement non-preemptive section support.

Re-introduce NP sections in the configuration and in litmus.h. Remove the old
np_flag from rt_param.

If CONFIG_NP_SECTION is disabled, then all non-preemptive section checks are
constant expressions which should get removed by the dead code elimination
during optimization.

Instead of re-implementing sys_exit_np(), we simply repurposed sched_yield()
for calling into the scheduler to trigger delayed preemptions.

2 files changed, 19 insertions, 2 deletions

diff --git a/litmus/Kconfig b/litmus/Kconfig
index 5556ae5cba45..874794f64af1 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -2,6 +2,17 @@ menu "LITMUS^RT"
 
 menu "Real-Time Synchronization"
 
+config NP_SECTION
+        bool "Non-preemptive section support"
+        default n
+        help
+          Allow tasks to become non-preemptable.
+          Note that plugins still need to explicitly support non-preemptivity.
+          Currently, only GSN-EDF and PSN-EDF have such support.
+
+          This is required to support the FMLP.
+          If disabled, all tasks will be considered preemptable at all times.
+
 config SRP
         bool "Stack Resource Policy (SRP)"
         default n
@@ -13,7 +24,7 @@ config SRP
 
 config FMLP
         bool "FMLP support"
-#       depends on NP_SECTION
+        depends on NP_SECTION
         default n
         help
           Include support for deterministic multiprocessor real-time
diff --git a/litmus/sched_litmus.c b/litmus/sched_litmus.c
index 64ad5db07795..c1fc7748e590 100644
--- a/litmus/sched_litmus.c
+++ b/litmus/sched_litmus.c
@@ -177,7 +177,13 @@ static void dequeue_task_litmus(struct rq *rq, struct task_struct *p, int sleep)
 static void yield_task_litmus(struct rq *rq)
 {
         BUG_ON(rq->curr != current);
-        litmus->complete_job();
+        /* sched_yield() is called to trigger delayed preemptions.
+         * Thus, mark the current task as needing to be rescheduled.
+         * This will cause the scheduler plugin to be invoked, which can
+         * then determine if a preemption is still required.
+         */
+        clear_exit_np(current);
+        set_tsk_need_resched(current);
 }
 
 /* Plugins are responsible for this.