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

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Date:   Wed, 15 Mar 2017 11:03:02 +0000
From:   Juri Lelli <juri.lelli@....com>
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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH] sched/deadline: Add missing update_rq_clock() in
 dl_task_timer()

Hi,

On 06/03/17 21:51, 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
>  Hardware name: LENOVO ThinkCentre M8500t-N000/SHARKBAY, BIOS FBKTC1AUS 02/16/2016
>  Call Trace:
>   <IRQ>
>   dump_stack+0x85/0xc4
>   __warn+0x172/0x1b0
>   warn_slowpath_fmt+0xb4/0xf0
>   ? __warn+0x1b0/0x1b0
>   ? debug_check_no_locks_freed+0x2c0/0x2c0
>   ? cpudl_set+0x3d/0x2b0
>   replenish_dl_entity+0x71e/0xc40
>   enqueue_task_dl+0x2ea/0x12e0
>   ? dl_task_timer+0x777/0x990
>   ? __hrtimer_run_queues+0x270/0xa50
>   dl_task_timer+0x316/0x990
>   ? enqueue_task_dl+0x12e0/0x12e0
>   ? enqueue_task_dl+0x12e0/0x12e0
>   __hrtimer_run_queues+0x270/0xa50
>   ? hrtimer_cancel+0x20/0x20
>   ? hrtimer_interrupt+0x119/0x600
>   hrtimer_interrupt+0x19c/0x600
>   ? trace_hardirqs_off+0xd/0x10
>   local_apic_timer_interrupt+0x74/0xe0
>   smp_apic_timer_interrupt+0x76/0xa0
>   apic_timer_interrupt+0x93/0xa0
> 
> The DL task will be migrated to a suitable later deadline rq once the DL 
> timer fires and currnet rq is offline. The rq clock of the new rq should 
> be updated. This patch fixes it by updating the rq clock after holding 
> the new rq's rq lock.
> 
> Cc: Juri Lelli <juri.lelli@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Matt Fleming <matt@...eblueprint.co.uk>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  kernel/sched/deadline.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> 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);

Looks good to me.

Acked-by: Juri Lelli <juri.lelli@....com>

Thanks,

- Juri