linux-kernel - Re: [PATCH] hrtimer: select housekeeping CPU during migration

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Date: Sun, 11 Feb 2024 11:37:52 -0500
From: Waiman Long <longman@...hat.com>
To: Costa Shulyupin <costa.shul@...hat.com>,
 Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hrtimer: select housekeeping CPU during migration


On 2/11/24 08:52, Costa Shulyupin wrote:
> because during CPU deactivation a timer can migrate
> to isolated CPU and break CPU isolation.
>
> For reference see function get_nohz_timer_target,
> which selects CPU for new timers from housekeeping_cpumask(HK_TYPE_TIMER)
>
> Inspired by Waiman Long <longman@...hat.com>
>
> Signed-off-by: Costa Shulyupin <costa.shul@...hat.com>

Nit: It is unusual to begin the commit log with "because".

Other than that, the patch looks good to me.

Reviewed-by:  Waiman Long <longman@...hat.com>

> ---
>   kernel/time/hrtimer.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index f82997cf53b6..460d916e24b7 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -2227,7 +2227,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
>   int hrtimers_cpu_dying(unsigned int dying_cpu)
>   {
>   	struct hrtimer_cpu_base *old_base, *new_base;
> -	int i, ncpu = cpumask_first(cpu_active_mask);
> +	int i, ncpu = cpumask_any_and(cpu_active_mask, housekeeping(HK_TYPE_TIMER));
>   	pr_debug("ncpu=%d, dying_cpu=%d\n", ncpu, dying_cpu);
>   
>   	tick_cancel_sched_timer(dying_cpu);