linux-kernel - Re: [tip:smp/hotplug] cpu/hotplug: Split out cpu down functions

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Date:	Wed, 2 Mar 2016 17:37:52 -0500
From:	"Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
To:	arjan@...ux.intel.com, paulmck@...ux.vnet.ibm.com, riel@...hat.com,
	peterz@...radead.org, tj@...nel.org, rusty@...tcorp.com.au,
	akpm@...ux-foundation.org, pjt@...gle.com,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, srivatsa@....edu,
	rafael.j.wysocki@...el.com, bigeasy@...utronix.de, oleg@...hat.com,
	hpa@...or.com, rostedt@...dmis.org, mingo@...nel.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:smp/hotplug] cpu/hotplug: Split out cpu down functions

On 3/1/16 2:52 PM, tip-bot for Thomas Gleixner wrote:
> Commit-ID:  984581728eb4b2e10baed3d606f85a119795b207
> Gitweb:     http://git.kernel.org/tip/984581728eb4b2e10baed3d606f85a119795b207
> Author:     Thomas Gleixner <tglx@...utronix.de>
> AuthorDate: Fri, 26 Feb 2016 18:43:25 +0000
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Tue, 1 Mar 2016 20:36:53 +0100
> 
> cpu/hotplug: Split out cpu down functions
> 
> Split cpu_down in separate functions in preparation for state machine
> conversion.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: linux-arch@...r.kernel.org
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Rafael Wysocki <rafael.j.wysocki@...el.com>
> Cc: "Srivatsa S. Bhat" <srivatsa@....edu>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Arjan van de Ven <arjan@...ux.intel.com>
> Cc: Sebastian Siewior <bigeasy@...utronix.de>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Paul McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Paul Turner <pjt@...gle.com>
> Link: http://lkml.kernel.org/r/20160226182340.511796562@linutronix.de
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---

Reviewed-by: Srivatsa S. Bhat <srivatsa@...il.mit.edu>

Regards,
Srivatsa S. Bhat

>  kernel/cpu.c | 83 ++++++++++++++++++++++++++++++++++++++----------------------
>  1 file changed, 53 insertions(+), 30 deletions(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 15a4136..0b5d259 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -266,11 +266,6 @@ static int bringup_cpu(unsigned int cpu)
>  }
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> -
> -static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
> -{
> -	BUG_ON(cpu_notify(val, cpu));
> -}
>  EXPORT_SYMBOL(register_cpu_notifier);
>  EXPORT_SYMBOL(__register_cpu_notifier);
>  
> @@ -353,6 +348,25 @@ static inline void check_for_tasks(int dead_cpu)
>  	read_unlock(&tasklist_lock);
>  }
>  
> +static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
> +{
> +	BUG_ON(cpu_notify(val, cpu));
> +}
> +
> +static int notify_down_prepare(unsigned int cpu)
> +{
> +	int err, nr_calls = 0;
> +
> +	err = __cpu_notify(CPU_DOWN_PREPARE, cpu, -1, &nr_calls);
> +	if (err) {
> +		nr_calls--;
> +		__cpu_notify(CPU_DOWN_FAILED, cpu, nr_calls, NULL);
> +		pr_warn("%s: attempt to take down CPU %u failed\n",
> +				__func__, cpu);
> +	}
> +	return err;
> +}
> +
>  /* Take this CPU down. */
>  static int take_cpu_down(void *_param)
>  {
> @@ -371,29 +385,9 @@ static int take_cpu_down(void *_param)
>  	return 0;
>  }
>  
> -/* Requires cpu_add_remove_lock to be held */
> -static int _cpu_down(unsigned int cpu, int tasks_frozen)
> +static int takedown_cpu(unsigned int cpu)
>  {
> -	int err, nr_calls = 0;
> -
> -	if (num_online_cpus() == 1)
> -		return -EBUSY;
> -
> -	if (!cpu_online(cpu))
> -		return -EINVAL;
> -
> -	cpu_hotplug_begin();
> -
> -	cpuhp_tasks_frozen = tasks_frozen;
> -
> -	err = __cpu_notify(CPU_DOWN_PREPARE, cpu, -1, &nr_calls);
> -	if (err) {
> -		nr_calls--;
> -		__cpu_notify(CPU_DOWN_FAILED, cpu, nr_calls, NULL);
> -		pr_warn("%s: attempt to take down CPU %u failed\n",
> -			__func__, cpu);
> -		goto out_release;
> -	}
> +	int err;
>  
>  	/*
>  	 * By now we've cleared cpu_active_mask, wait for all preempt-disabled
> @@ -426,7 +420,7 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  		/* CPU didn't die: tell everyone.  Can't complain. */
>  		cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
>  		irq_unlock_sparse();
> -		goto out_release;
> +		return err;
>  	}
>  	BUG_ON(cpu_online(cpu));
>  
> @@ -449,11 +443,40 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  	/* This actually kills the CPU. */
>  	__cpu_die(cpu);
>  
> -	/* CPU is completely dead: tell everyone.  Too late to complain. */
>  	tick_cleanup_dead_cpu(cpu);
> -	cpu_notify_nofail(CPU_DEAD, cpu);
> +	return 0;
> +}
>  
> +static int notify_dead(unsigned int cpu)
> +{
> +	cpu_notify_nofail(CPU_DEAD, cpu);
>  	check_for_tasks(cpu);
> +	return 0;
> +}
> +
> +/* Requires cpu_add_remove_lock to be held */
> +static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
> +{
> +	int err;
> +
> +	if (num_online_cpus() == 1)
> +		return -EBUSY;
> +
> +	if (!cpu_online(cpu))
> +		return -EINVAL;
> +
> +	cpu_hotplug_begin();
> +
> +	cpuhp_tasks_frozen = tasks_frozen;
> +
> +	err = notify_down_prepare(cpu);
> +	if (err)
> +		goto out_release;
> +	err = takedown_cpu(cpu);
> +	if (err)
> +		goto out_release;
> +
> +	notify_dead(cpu);
>  
>  out_release:
>  	cpu_hotplug_done();
>