linux-kernel - Re: [PATCH] sched: Fix stop_one_cpu

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Date:   Wed, 11 Oct 2023 15:26:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kuyo Chang (張建文) <Kuyo.Chang@...iatek.com>
Cc:     "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        "vschneid@...hat.com" <vschneid@...hat.com>,
        "bristot@...hat.com" <bristot@...hat.com>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "bsegall@...gle.com" <bsegall@...gle.com>,
        "mgorman@...e.de" <mgorman@...e.de>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH] sched: Fix stop_one_cpu_nowait() vs hotplug

On Wed, Oct 11, 2023 at 03:24:19AM +0000, Kuyo Chang (張建文) wrote:
> On Tue, 2023-10-10 at 22:04 +0200, Peter Zijlstra wrote:
> >  	 
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> >  On Tue, Oct 10, 2023 at 04:57:47PM +0200, Peter Zijlstra wrote:
> > > On Tue, Oct 10, 2023 at 02:40:22PM +0000, Kuyo Chang (張建文) wrote:
> > 
> > > > It is running good so far(more than a week)on hotplug/set
> > affinity
> > > > stress test. I will keep it testing and report back if it happens
> > > > again.
> > > 
> > > OK, I suppose I should look at writing a coherent Changelog for
> > this
> > > then...
> > 
> > Something like the below... ?
> > 
> Thanks for illustrate the race scenario. It looks good to me.
> But how about RT? Does RT also need this invocations as below?
> 
> ---
>  kernel/sched/rt.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index e93b69ef919b..6aaf0a3d6081 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2063,9 +2063,11 @@ static int push_rt_task(struct rq *rq, bool
> pull)
>                  */
>                 push_task = get_push_task(rq);
>                 if (push_task) {
> +                       preempt_disable();
>                         raw_spin_rq_unlock(rq);
>                         stop_one_cpu_nowait(rq->cpu, push_cpu_stop,
>                                             push_task, &rq->push_work);
> +                       preempt_enable();
>                         raw_spin_rq_lock(rq);
>                 }
> 
> @@ -2402,9 +2404,11 @@ static void pull_rt_task(struct rq *this_rq)
>                 double_unlock_balance(this_rq, src_rq);
> 
>                 if (push_task) {
> +                       preempt_disable();
>                         raw_spin_rq_unlock(this_rq);
>                         stop_one_cpu_nowait(src_rq->cpu, push_cpu_stop,
>                                             push_task, &src_rq-
> >push_work);
> +                       preempt_enable();
>                         raw_spin_rq_lock(this_rq);
>                 }
>         }

bah, clearly git-grep didn't work for me last night, I'll go fix up.