linux-kernel - Re: [PATCH RT 2/8] sched: __set_cpus_allowed_ptr: Check cpus_mask, not cpus

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Date:   Tue, 17 Sep 2019 16:57:29 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Scott Wood <swood@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Clark Williams <williams@...hat.com>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH RT 2/8] sched: __set_cpus_allowed_ptr: Check cpus_mask,
 not cpus_ptr

On 2019-07-27 00:56:32 [-0500], Scott Wood wrote:
> This function is concerned with the long-term cpu mask, not the
> transitory mask the task might have while migrate disabled.  Before
> this patch, if a task was migrate disabled at the time
> __set_cpus_allowed_ptr() was called, and the new mask happened to be
> equal to the cpu that the task was running on, then the mask update
> would be lost.

lost as in "would not be carried out" I assume.

> Signed-off-by: Scott Wood <swood@...hat.com>
> ---
>  kernel/sched/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c3407707e367..6e643d656d71 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1218,7 +1218,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
>  		goto out;
>  	}
>  
> -	if (cpumask_equal(p->cpus_ptr, new_mask))
> +	if (cpumask_equal(&p->cpus_mask, new_mask))
>  		goto out;
>  
>  	if (!cpumask_intersects(new_mask, cpu_valid_mask)) {


Sebastian