linux-kernel - Re: [PATCH v8 -tip 24/26] sched: Move core-scheduler interfacing code to a new file

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Date:   Mon, 2 Nov 2020 21:58:22 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        torvalds@...ux-foundation.org, fweisbec@...il.com,
        keescook@...omium.org, 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>, vineeth@...byteword.org,
        Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Agata Gruza <agata.gruza@...el.com>,
        Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
        graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
        pjt@...gle.com, rostedt@...dmis.org, derkling@...gle.com,
        benbjiang@...cent.com,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        James.Bottomley@...senpartnership.com, OWeisse@...ch.edu,
        Dhaval Giani <dhaval.giani@...cle.com>,
        Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com,
        chris.hyser@...cle.com, "Paul E. McKenney" <paulmck@...nel.org>,
        Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH v8 -tip 24/26] sched: Move core-scheduler interfacing
 code to a new file

On Mon, Oct 26, 2020 at 09:05:52AM +0800, Li, Aubrey wrote:
[..]
> > +int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2)
> > +{
> > +	struct sched_core_task_write_tag wr = {}; /* for stop machine. */
> > +	bool sched_core_put_after_stopper = false;
> > +	unsigned long cookie;
> > +	int ret = -ENOMEM;
> > +
> > +	mutex_lock(&sched_core_tasks_mutex);
> > +
> > +	/*
> > +	 * NOTE: sched_core_get() is done by sched_core_alloc_task_cookie() or
> > +	 *       sched_core_put_task_cookie(). However, sched_core_put() is done
> > +	 *       by this function *after* the stopper removes the tasks from the
> > +	 *       core queue, and not before. This is just to play it safe.
> > +	 */
> > +	if (t2 == NULL) {
> > +		if (t1->core_task_cookie) {
> > +			sched_core_put_task_cookie(t1->core_task_cookie);
> > +			sched_core_put_after_stopper = true;
> > +			wr.tasks[0] = t1; /* Keep wr.cookies[0] reset for t1. */
> > +		}
> > +	} else if (t1 == t2) {
> > +		/* Assign a unique per-task cookie solely for t1. */
> > +
> > +		cookie = sched_core_alloc_task_cookie();
> > +		if (!cookie)
> > +			goto out_unlock;
> > +
> > +		if (t1->core_task_cookie) {
> > +			sched_core_put_task_cookie(t1->core_task_cookie);
> > +			sched_core_put_after_stopper = true;
> > +		}
> > +		wr.tasks[0] = t1;
> > +		wr.cookies[0] = cookie;
> > +	} else
> > +	/*
> > +	 * 		t1		joining		t2
> > +	 * CASE 1:
> > +	 * before	0				0
> > +	 * after	new cookie			new cookie
> > +	 *
> > +	 * CASE 2:
> > +	 * before	X (non-zero)			0
> > +	 * after	0				0
> > +	 *
> > +	 * CASE 3:
> > +	 * before	0				X (non-zero)
> > +	 * after	X				X
> > +	 *
> > +	 * CASE 4:
> > +	 * before	Y (non-zero)			X (non-zero)
> > +	 * after	X				X
> > +	 */
> > +	if (!t1->core_task_cookie && !t2->core_task_cookie) {
> > +		/* CASE 1. */
> > +		cookie = sched_core_alloc_task_cookie();
> > +		if (!cookie)
> > +			goto out_unlock;
> > +
> > +		/* Add another reference for the other task. */
> > +		if (!sched_core_get_task_cookie(cookie)) {
> > +			return -EINVAL;
> 
> ret = -EINVAL; mutex is not released otherwise... 

Good find and will fix.

Minor suggestion: Could you truncate your emails when replying?

thanks,

 - Joel