Re: [PATCH 11/12] task_isolation: kick_all_cpus_sync: don't kick isolated cpus

[Frederic Weisbecker]

On Wed, Mar 04, 2020 at 04:15:24PM +0000, Alex Belits wrote:
> From: Yuri Norov <ynorov@xxxxxxxxxxx>
> 
> Make sure that kick_all_cpus_sync() does not call CPUs that are running
> isolated tasks.
> 
> Signed-off-by: Alex Belits <abelits@xxxxxxxxxxx>
> ---
>  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
>