linux-kernel - Re: [PATCH] sched/deadline: Add missing update_rq_clock() in dl_task

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Date:   Tue, 7 Mar 2017 13:35:29 +0000
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Juri Lelli <juri.lelli@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/deadline: Add missing update_rq_clock() in
 dl_task_timer()

On Mon, 06 Mar, at 09:51:28PM, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.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@...eblueprint.co.uk>