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Date:   Wed, 25 Nov 2020 12:15:41 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
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        "Paul E. McKenney" <paulmck@kernel.org>,
        Tim Chen <tim.c.chen@intel.com>
Subject: Re: [PATCH -tip 22/32] sched: Split the cookie and setup per-task
 cookie on fork
Message-ID: <20201125111541.GU2414@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:

> +/*
> + * Ensure that the task has been requeued. The stopper ensures that the task cannot
> + * be migrated to a different CPU while its core scheduler queue state is being updated.
> + * It also makes sure to requeue a task if it was running actively on another CPU.
> + */
> +static int sched_core_task_join_stopper(void *data)
> +{
> +	struct sched_core_task_write_tag *tag = (struct sched_core_task_write_tag *)data;
> +	int i;
> +
> +	for (i = 0; i < 2; i++)
> +		sched_core_tag_requeue(tag->tasks[i], tag->cookies[i], false /* !group */);
> +
> +	return 0;
> +}
> +
> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2)
> +{

> +	stop_machine(sched_core_task_join_stopper, (void *)&wr, NULL);

> +}

This is *REALLY* terrible...