linux-kernel - Re: [PATCH 5/6] sched/isolation: Introduce isolated task work

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Message-ID: <20250411102555.GA5322@redhat.com>
Date: Fri, 11 Apr 2025 12:25:56 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Michal Hocko <mhocko@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org
Subject: Re: [PATCH 5/6] sched/isolation: Introduce isolated task work

I know nothing about this code so I can't review, but let me
ask anyway...

On 04/10, Frederic Weisbecker wrote:
>
> +int __isolated_task_work_queue(void)
> +{
> +	unsigned long flags;
> +	int ret;
> +
> +	if (current->flags & PF_KTHREAD)
> +		return -EINVAL;

What about PF_USER_WORKER's ? IIUC, these (in fact kernel) threads
never return to userspace and never call task_work_run().

Or PF_IO_WORKER's, they too run only in kernel mode... But iirc they
do call task_work_run().

> +	local_irq_save(flags);
> +	if (task_work_queued(&current->nohz_full_work)) {
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	ret = task_work_add(current, &current->nohz_full_work, TWA_RESUME);
> +out:
> +	local_irq_restore(flags);
> +	return ret;

Hmm, why not

	local_irq_save(flags);
	if (task_work_queued(...))
		ret = 0;
	else
		ret = task_work_add(...);

?

Oleg.