Commit-ID: a79ec89fd8459f0de850898f432a2a57d60e64de
Gitweb: http://git.kernel.org/tip/a79ec89fd8459f0de850898f432a2a57d60e64de
Author: Kirill Tkhai <tkhai@xxxxxxxxx>
AuthorDate: Mon, 16 Feb 2015 15:38:34 +0300
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 18 Feb 2015 14:27:31 +0100
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 <fengguang.wu@xxxxxxxxx>
Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
[ Wrote comment. ]
Cc: Juri Lelli <juri.lelli@xxxxxxx>
Fixes: 1019a359d3dc ("sched/deadline: Fix stale yield state")
Link: http://lkml.kernel.org/r/1374601424090314@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/deadline.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e88847d..9908c95 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);
--
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