Re: [PATCH] sched/deadline: Add missing update_rq_clock() in dl_task_timer()

Matt Fleming
2017-03-07T13:42:42Z

On Mon, 06 Mar, at 09:51:28PM, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> The following warning can be triggered by hot-unplugging the CPU
> on which an active SCHED_DEADLINE task is running on:
>
> ------------[ cut here ]------------
> WARNING: CPU: 7 PID: 0 at kernel/sched/sched.h:833 replenish_dl_entity+0x71e/0xc40
> rq->clock_update_flags < RQCF_ACT_SKIP
> CPU: 7 PID: 0 Comm: swapper/7 Tainted: G B 4.11.0-rc1+ #24

[...]

> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 99b2c33..c6db3fd 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -638,6 +638,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
> lockdep_unpin_lock(&rq->lock, rf.cookie);
> rq = dl_task_offline_migration(rq, p);
> rf.cookie = lockdep_pin_lock(&rq->lock);
> + update_rq_clock(rq);
>
> /*
> * Now that the task has been migrated to the new RQ and we

Yeah, I guess the reason we can't use the rq_repin_lock() function is
because of all the DL double rq locking going on inside of
dl_task_offline_migration().

I'd definitely like someone else to verify, but this looks OK to me.

Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>