Bugfix: PSN-EDF should only requeue tasks that are not scheduled

Requeue a task that is already scheduled will cause it to be effectively
in the runqueue twice since scheduled tasks are conceptually the head
of the queue. If a task is still scheduled, then schedule() will do the
right thing and do the requeuing if necessary.

This fixes crashes reported by Glenn and Andrea.

1 files changed, 10 insertions, 11 deletions

diff --git a/litmus/sched_psn_edf.c b/litmus/sched_psn_edf.c
index 3a93124e24f6..d37f045768d5 100644
--- a/litmus/sched_psn_edf.c
+++ b/litmus/sched_psn_edf.c
@@ -258,28 +258,27 @@ static void psnedf_task_wake_up(struct task_struct *task)
                 release_at(task, now);
                 sched_trace_task_release(task);
         }
-        requeue(task, edf);
+
+        /* Only add to ready queue if it is not the currently-scheduled
+         * task. This could be the case if a task was woken up concurrently
+         * on a remote CPU before the executing CPU got around to actually
+         * de-scheduling the task, i.e., wake_up() raced with schedule()
+         * and won.
+         */
+        if (pedf->scheduled != task)
+                requeue(task, edf);
+
         spin_unlock_irqrestore(&pedf->slock, flags);
         TRACE_TASK(task, "wake up done\n");
 }
 
 static void psnedf_task_block(struct task_struct *t)
 {
-        psnedf_domain_t *pedf = task_pedf(t);
-
         /* only running tasks can block, thus t is in no queue */
         TRACE_TASK(t, "block at %llu, state=%d\n", litmus_clock(), t->state);
 
         BUG_ON(!is_realtime(t));
         BUG_ON(is_queued(t));
-
-        /* if this task is dead, then we need to reset pedf->schedule now
-         * as we might get rescheduled before task_exit executes
-         */
-        if(unlikely(t->state == TASK_DEAD)) {
-                TRACE_TASK(t, "Dead, setting scheduled = NULL\n");
-                pedf->scheduled = NULL;
-        }
 }
 
 static void psnedf_task_exit(struct task_struct * t)