linux-kernel - Re: [PATCH 11/12] task_isolation: kick_all_cpus

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Date:   Fri, 6 Mar 2020 16:34:47 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Alex Belits <abelits@...vell.com>
Cc:     "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Prasun Kapoor <pkapoor@...vell.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-mm@...r.kernel.org" <linux-mm@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick
 isolated cpus

On Wed, Mar 04, 2020 at 04:15:24PM +0000, Alex Belits wrote:
> From: Yuri Norov <ynorov@...vell.com>
> 
> Make sure that kick_all_cpus_sync() does not call CPUs that are running
> isolated tasks.
> 
> Signed-off-by: Alex Belits <abelits@...vell.com>
> ---
>  kernel/smp.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 3a8bcbdd4ce6..d9b4b2fedfed 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -731,9 +731,21 @@ static void do_nothing(void *unused)
>   */
>  void kick_all_cpus_sync(void)
>  {
> +	struct cpumask mask;
> +
>  	/* Make sure the change is visible before we kick the cpus */
>  	smp_mb();
> -	smp_call_function(do_nothing, NULL, 1);
> +
> +	preempt_disable();
> +#ifdef CONFIG_TASK_ISOLATION
> +	cpumask_clear(&mask);
> +	task_isolation_cpumask(&mask);
> +	cpumask_complement(&mask, &mask);
> +#else
> +	cpumask_setall(&mask);
> +#endif
> +	smp_call_function_many(&mask, do_nothing, NULL, 1);
> +	preempt_enable();
>  }

That looks very dangerous, the callers of kick_all_cpus_sync() want to
sync all CPUs for a reason. You will rather need to fix the callers.

Thanks.

>  EXPORT_SYMBOL_GPL(kick_all_cpus_sync);
>  
> -- 
> 2.20.1
>