From a79ec89fd8459f0de850898f432a2a57d60e64de Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Mon, 16 Feb 2015 15:38:34 +0300 Subject: [PATCH] sched/dl: Prevent enqueue of a sleeping task in dl_task_timer() A deadline task may be throttled and dequeued at the same time. This happens, when it becomes throttled in schedule(), which is called to go to sleep: current->state = TASK_INTERRUPTIBLE; schedule() deactivate_task() dequeue_task_dl() update_curr_dl() start_dl_timer() __dequeue_task_dl() prev->on_rq = 0; Later the timer fires, but the task is still dequeued: dl_task_timer() enqueue_task_dl() /* queues on dl_rq; on_rq remains 0 */ Someone wakes it up: try_to_wake_up() enqueue_dl_entity() BUG_ON(on_dl_rq()) Patch fixes this problem, it prevents queueing !on_rq tasks on dl_rq. Reported-by: Fengguang Wu Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra (Intel) [ Wrote comment. ] Cc: Juri Lelli Fixes: 1019a359d3dc ("sched/deadline: Fix stale yield state") Link: http://lkml.kernel.org/r/1374601424090314@web4j.yandex.ru Signed-off-by: Ingo Molnar --- kernel/sched/deadline.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index e88847d9fc6a..9908c950d776 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -535,6 +535,26 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) sched_clock_tick(); update_rq_clock(rq); + + /* + * If the throttle happened during sched-out; like: + * + * schedule() + * deactivate_task() + * dequeue_task_dl() + * update_curr_dl() + * start_dl_timer() + * __dequeue_task_dl() + * prev->on_rq = 0; + * + * We can be both throttled and !queued. Replenish the counter + * but do not enqueue -- wait for our wakeup to do that. + */ + if (!task_on_rq_queued(p)) { + replenish_dl_entity(dl_se, dl_se); + goto unlock; + } + enqueue_task_dl(rq, p, ENQUEUE_REPLENISH); if (dl_task(rq->curr)) check_preempt_curr_dl(rq, p, 0);