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Date:   Wed, 25 Nov 2020 13:54:47 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     Nishanth Aravamudan <naravamudan@digitalocean.com>,
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Subject: Re: [PATCH -tip 22/32] sched: Split the cookie and setup per-task
 cookie on fork
Message-ID: <20201125125447.GV2414@hirez.programming.kicks-ass.net>
References: <20201117232003.3580179-1-joel@joelfernandes.org>
 <20201117232003.3580179-23-joel@joelfernandes.org>
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On Tue, Nov 17, 2020 at 06:19:52PM -0500, Joel Fernandes (Google) wrote:
> +/* Per-task interface */
> +static unsigned long sched_core_alloc_task_cookie(void)
> +{
> +	struct sched_core_cookie *ptr =
> +		kmalloc(sizeof(struct sched_core_cookie), GFP_KERNEL);
> +
> +	if (!ptr)
> +		return 0;
> +	refcount_set(&ptr->refcnt, 1);
> +
> +	/*
> +	 * NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
> +	 * is done after the stopper runs.
> +	 */
> +	sched_core_get();
> +	return (unsigned long)ptr;
> +}
> +
> +static bool sched_core_get_task_cookie(unsigned long cookie)
> +{
> +	struct sched_core_cookie *ptr = (struct sched_core_cookie *)cookie;
> +
> +	/*
> +	 * NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
> +	 * is done after the stopper runs.
> +	 */
> +	sched_core_get();
> +	return refcount_inc_not_zero(&ptr->refcnt);
> +}
> +
> +static void sched_core_put_task_cookie(unsigned long cookie)
> +{
> +	struct sched_core_cookie *ptr = (struct sched_core_cookie *)cookie;
> +
> +	if (refcount_dec_and_test(&ptr->refcnt))
> +		kfree(ptr);
> +}

> +	/*
> +	 * 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.
> +	 */

So for no reason what so ever you've made the code more difficult?