linux-kernel - Re: [PATCH v5 1/3] sched: Use user_cpus_ptr for saving user provided cpumask in sched

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Message-ID: <Yvyq5GBtU+XxLSaP@worktop.programming.kicks-ass.net>
Date:   Wed, 17 Aug 2022 10:46:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Will Deacon <will@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v5 1/3] sched: Use user_cpus_ptr for saving user provided
 cpumask in sched_setaffinity()

On Tue, Aug 16, 2022 at 03:27:32PM -0400, Waiman Long wrote:
> @@ -8079,10 +8056,11 @@ int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
>  #endif
>  
>  static int
> -__sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
> +__sched_setaffinity(struct task_struct *p, const struct cpumask *mask, bool save_mask)
>  {
>  	int retval;
>  	cpumask_var_t cpus_allowed, new_mask;
> +	struct cpumask *user_mask = NULL;
>  
>  	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL))
>  		return -ENOMEM;

Please move that retval down so the variable declarations are properly
ordered again.

> @@ -8098,8 +8076,33 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
>  	retval = dl_task_check_affinity(p, new_mask);
>  	if (retval)
>  		goto out_free_new_mask;
> +
> +	/*
> +	 * Save the user requested mask into user_cpus_ptr if save_mask set.
> +	 * pi_lock is used for protecting user_cpus_ptr.
> +	 */
> +	if (save_mask && !p->user_cpus_ptr) {
> +		user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
> +
> +		if (!user_mask) {
> +			retval = -ENOMEM;
> +			goto out_free_new_mask;
> +		}
> +	}
> +	if (save_mask) {
> +		unsigned long flags;
> +
> +		raw_spin_lock_irqsave(&p->pi_lock, flags);
> +		if (!p->user_cpus_ptr) {
> +			p->user_cpus_ptr = user_mask;
> +			user_mask = NULL;
> +		}
> +
> +		cpumask_copy(p->user_cpus_ptr, mask);
> +		raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> +	}

How about:

	if (save_mask) {
		if (!p->user_cpus_ptr) {
			...
		}
		...
	}

?