linux-kernel - Re: [RFC PATCH v3 00/16] Core scheduling v3

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Message-ID: <63f81e82-cd5b-9095-c153-cb638f5dde08@linux.intel.com>
Date:   Wed, 18 Sep 2019 14:27:27 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Julien Desfossez <jdesfossez@...italocean.com>
Cc:     Dario Faggioli <dfaggioli@...e.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Aaron Lu <aaron.lu@...ux.alibaba.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3

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