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To:     Julien Desfossez <jdesfossez@digitalocean.com>
Cc:     Dario Faggioli <dfaggioli@suse.com>,
        "Li, Aubrey" <aubrey.li@linux.intel.com>,
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        Ingo Molnar <mingo@kernel.org>,
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From:   Tim Chen <tim.c.chen@linux.intel.com>
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Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3
Message-ID: <63f81e82-cd5b-9095-c153-cb638f5dde08@linux.intel.com>
Date:   Wed, 18 Sep 2019 14:27:27 -0700
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Sender: linux-kernel-owner@vger.kernel.org
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On 9/4/19 6:44 PM, Julien Desfossez wrote:

> +
> +static void coresched_idle_worker_fini(struct rq *rq)
> +{
> +	if (rq->core_idle_task) {
> +		kthread_stop(rq->core_idle_task);
> +		rq->core_idle_task = NULL;
> +	}

During testing, I have found access of rq->core_idle_task as
NULL pointer from other cpus (other than the cpu executing the stop_machine
function) when you toggle cpu.tag of the cgroup.
Doing locking here is tricky because the rq lock is being
transitioned from core lock to per run queue lock.  As a fix,
I made coresched_idle_worker_fini a null function, and not
to null out the core_idle_task.

Tim