sched/dl: Prevent enqueue of a sleeping task in dl_task_timer()
commita79ec89fd8459f0de850898f432a2a57d60e64de
authorKirill Tkhai <tkhai@yandex.ru>
Mon, 16 Feb 2015 12:38:34 +0000 (16 15:38 +0300)
committerIngo Molnar <mingo@kernel.org>
Wed, 18 Feb 2015 13:27:31 +0000 (18 14:27 +0100)
tree23b42d39bfc96342d22cd55dade4fef1c52f89ef
parent3960c8c0c7891dfc0f7be687cbdabb0d6916d614
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@intel.com>
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[ Wrote comment. ]
Cc: Juri Lelli <juri.lelli@arm.com>
Fixes: 1019a359d3dc ("sched/deadline: Fix stale yield state")
Link: http://lkml.kernel.org/r/1374601424090314@web4j.yandex.ru
Signed-off-by: Ingo Molnar <mingo@kernel.org>
kernel/sched/deadline.c