sched: Fix runnable condition for stoptask

Heiko reported that the TASK_RUNNING check is not sufficient for
CONFIG_PREEMPT=y since we can get preempted with !TASK_RUNNING.

He suggested adding a ->se.on_rq test to the existing TASK_RUNNING
one, however TASK_RUNNING will always have ->se.on_rq, so we might as
well reduce that to a single test.

[ stop tasks should never get preempted, but its good to handle
  this case correctly should this ever happen ]

Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched_stoptask.c b/kernel/sched_stoptask.c
index 45bddc0..755483b 100644 (file)
--- a/kernel/sched_stoptask.c
+++ b/kernel/sched_stoptask.c
@@ -26,7 +26,7 @@ static struct task_struct *pick_next_task_stop(struct rq *rq)
 {
        struct task_struct *stop = rq->stop;
 
-       if (stop && stop->state == TASK_RUNNING)
+       if (stop && stop->se.on_rq)
                return stop;
 
        return NULL;