Fix BUG: enter gsnedf_schedule with entry->scheduled = NULL

This solves (? -- or at least solve one of the possible reasons for ;)
a BUG in sched_gsnedf where a real-time task could enter gsnedf_schedule
with an entry->schedule = NULL (and this is BAD!)

1 files changed, 11 insertions, 1 deletions

diff --git a/litmus/sched_gsn_edf.c b/litmus/sched_gsn_edf.c
index 9f256be86cf7..98c3c4bc3128 100644
--- a/litmus/sched_gsn_edf.c
+++ b/litmus/sched_gsn_edf.c
@@ -469,7 +469,7 @@ static struct task_struct* gsnedf_schedule(struct task_struct * prev)
                 if (entry->scheduled) {
                         /* not gonna be scheduled soon */
                         entry->scheduled->rt_param.scheduled_on = NO_CPU;
-                        TRACE_TASK(entry->scheduled, "scheduled_on = NO_CPU\n");
+                        TRACE_TASK(entry->scheduled, "gsnedf_schedule: scheduled_on = NO_CPU\n");
                 }
         } else
                 /* Only override Linux scheduler if we have a real-time task
@@ -578,8 +578,18 @@ static void gsnedf_task_block(struct task_struct *t)
 
         TRACE_TASK(t, "block at %llu\n", litmus_clock());
 
+
         /* unlink if necessary */
         spin_lock_irqsave(&gsnedf_lock, flags);
+
+        /* this is tricky: is gonna be unlinked _and_ rescheduled
+         * but if rescheduling decision is deferred scheduled_on
+         * will remain to current cpu and this may cause entry->scheduled
+         * (of some other task) to be rewritten
+         */
+        t->rt_param.scheduled_on = NO_CPU;
+        TRACE_TASK(t, "gsnedf_task_block: scheduled_on = NO_CPU\n");
+
         unlink(t);
         spin_unlock_irqrestore(&gsnedf_lock, flags);