linux-kernel - Re: [patch 06/20] cpufreq: Use cpuhp_setup_state_nocalls

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Date:   Mon, 17 Apr 2017 09:44:38 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org
Subject: Re: [patch 06/20] cpufreq: Use cpuhp_setup_state_nocalls_locked()

On 15-04-17, 19:01, Thomas Gleixner wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> cpufreq holds get_online_cpus() while invoking cpuhp_setup_state_nocalls()
> to make subsys_interface_register() and the registration of hotplug calls
> atomic versus cpu hotplug.
> 
> cpuhp_setup_state_nocalls() invokes get_online_cpus() as well. This is
> correct, but prevents the conversion of the hotplug locking to a percpu
> rwsem.
> 
> Use cpuhp_setup_state_nocalls_locked() to avoid the nested call.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: linux-pm@...r.kernel.org
> 
> ---
>  drivers/cpufreq/cpufreq.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2473,9 +2473,10 @@ int cpufreq_register_driver(struct cpufr
>  		goto err_if_unreg;
>  	}
>  
> -	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "cpufreq:online",
> -					cpuhp_cpufreq_online,
> -					cpuhp_cpufreq_offline);
> +	ret = cpuhp_setup_state_nocalls_locked(CPUHP_AP_ONLINE_DYN,
> +					       "cpufreq:online",
> +					       cpuhp_cpufreq_online,
> +					       cpuhp_cpufreq_offline);
>  	if (ret < 0)
>  		goto err_if_unreg;
>  	hp_online = ret;
> @@ -2519,7 +2520,7 @@ int cpufreq_unregister_driver(struct cpu
>  	get_online_cpus();
>  	subsys_interface_unregister(&cpufreq_interface);
>  	remove_boost_sysfs_file();
> -	cpuhp_remove_state_nocalls(hp_online);
> +	cpuhp_remove_state_nocalls_locked(hp_online);
>  
>  	write_lock_irqsave(&cpufreq_driver_lock, flags);

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh