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    Subject[PATCH] sched/deadline: always enqueue on previous rq when dl_task_timer fires
    Date
    dl_task_timer() may fire on a different rq from where a task was removed
    after throttling. Since the call path is:

    dl_task_timer() ->
    enqueue_task_dl() ->
    enqueue_dl_entity() ->
    replenish_dl_entity()

    and replenish_dl_entity() uses dl_se's rq, we can't use current's rq
    in dl_task_timer(), but we need to lock the task's previous one.

    Signed-off-by: Juri Lelli <juri.lelli@arm.com>
    Tested-by: Wanpeng Li <wanpeng.li@linux.intel.com>
    Acked-by: Kirill Tkhai <ktkhai@parallels.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Kirill Tkhai <ktkhai@parallels.com>
    Cc: Juri Lelli <juri.lelli@gmail.com>
    Cc: linux-kernel@vger.kernel.org
    Fixes: 3960c8c0c789 ("sched: Make dl_task_time() use task_rq_lock()")
    ---
    kernel/sched/deadline.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
    index 3fa8fa6..f670cbb 100644
    --- a/kernel/sched/deadline.c
    +++ b/kernel/sched/deadline.c
    @@ -514,7 +514,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
    unsigned long flags;
    struct rq *rq;

    - rq = task_rq_lock(current, &flags);
    + rq = task_rq_lock(p, &flags);

    /*
    * We need to take care of several possible races here:
    @@ -569,7 +569,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
    push_dl_task(rq);
    #endif
    unlock:
    - task_rq_unlock(rq, current, &flags);
    + task_rq_unlock(rq, p, &flags);

    return HRTIMER_NORESTART;
    }
    --
    2.2.2


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