linux-kernel - Re: [PATCH] hrtimer: reset .hres_active and .online at appropriate points

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Message-ID: <87bjw7azyh.ffs@tglx>
Date: Thu, 16 Jan 2025 10:08:06 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Koichiro Den <koichiro.den@...onical.com>, linux-kernel@...r.kernel.org
Cc: anna-maria@...utronix.de, frederic@...nel.org, peterz@...radead.org
Subject: Re: [PATCH] hrtimer: reset .hres_active and .online at appropriate
 points

On Fri, Dec 20 2024 at 22:44, Koichiro Den wrote:

>  int hrtimers_prepare_cpu(unsigned int cpu);
>  #ifdef CONFIG_HOTPLUG_CPU
> +int hrtimers_cpu_starting(unsigned int cpu);

This does not compile for CONFIG_HOTPLUG_CPU=n

>  int hrtimers_cpu_dying(unsigned int cpu);
>  #else
>  #define hrtimers_cpu_dying	NULL
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 85fd7ac4561e..34f1a09349fc 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -2180,7 +2180,7 @@ static struct cpuhp_step cpuhp_hp_states[] = {
>  	},
>  	[CPUHP_AP_HRTIMERS_DYING] = {
>  		.name			= "hrtimers:dying",
> -		.startup.single		= NULL,
> +		.startup.single		= hrtimers_cpu_starting,
>  		.teardown.single	= hrtimers_cpu_dying,
>  	},
>  	[CPUHP_AP_TICK_DYING] = {
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index 80fe3749d2db..98f23c9341f5 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -2246,6 +2246,14 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
>  	}
>  }
>  
> +int hrtimers_cpu_starting(unsigned int cpu)
> +{
> +	struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);

this_cpu_ptr()

> +	cpu_base->online = 1;

With that setting cpu_base->online in the prepare_cpu() callback
does not make any sense.

I'll fix it up for you this time.

Thanks,

        tglx