linux-kernel - Re: [tip:smp/hotplug] cpu/hotplug: Restructure cpu

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Date:	Wed, 2 Mar 2016 17:36:23 -0500
From:	"Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
To:	tj@...nel.org, rafael.j.wysocki@...el.com, pjt@...gle.com,
	bigeasy@...utronix.de, arjan@...ux.intel.com, rostedt@...dmis.org,
	riel@...hat.com, paulmck@...ux.vnet.ibm.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	akpm@...ux-foundation.org, srivatsa@....edu, peterz@...radead.org,
	torvalds@...ux-foundation.org, oleg@...hat.com, hpa@...or.com,
	rusty@...tcorp.com.au, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:smp/hotplug] cpu/hotplug: Restructure cpu_up code

On 3/1/16 2:52 PM, tip-bot for Thomas Gleixner wrote:
> Commit-ID:  ba997462435f48ad1501320e9da8770fd40c59b1
> Gitweb:     http://git.kernel.org/tip/ba997462435f48ad1501320e9da8770fd40c59b1
> Author:     Thomas Gleixner <tglx@...utronix.de>
> AuthorDate: Fri, 26 Feb 2016 18:43:24 +0000
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Tue, 1 Mar 2016 20:36:53 +0100
> 
> cpu/hotplug: Restructure cpu_up code
> 
> Split out into separate functions, so we can convert it to a state machine.
> 
> 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/20160226182340.429389195@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 | 69 +++++++++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 47 insertions(+), 22 deletions(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 41a6cb8..15a4136 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -228,6 +228,43 @@ static int cpu_notify(unsigned long val, unsigned int cpu)
>  	return __cpu_notify(val, cpu, -1, NULL);
>  }
>  
> +/* Notifier wrappers for transitioning to state machine */
> +static int notify_prepare(unsigned int cpu)
> +{
> +	int nr_calls = 0;
> +	int ret;
> +
> +	ret = __cpu_notify(CPU_UP_PREPARE, cpu, -1, &nr_calls);
> +	if (ret) {
> +		nr_calls--;
> +		printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n",
> +				__func__, cpu);
> +		__cpu_notify(CPU_UP_CANCELED, cpu, nr_calls, NULL);
> +	}
> +	return ret;
> +}
> +
> +static int notify_online(unsigned int cpu)
> +{
> +	cpu_notify(CPU_ONLINE, cpu);
> +	return 0;
> +}
> +
> +static int bringup_cpu(unsigned int cpu)
> +{
> +	struct task_struct *idle = idle_thread_get(cpu);
> +	int ret;
> +
> +	/* Arch-specific enabling code. */
> +	ret = __cpu_up(cpu, idle);
> +	if (ret) {
> +		cpu_notify(CPU_UP_CANCELED, cpu);
> +		return ret;
> +	}
> +	BUG_ON(!cpu_online(cpu));
> +	return 0;
> +}
> +
>  #ifdef CONFIG_HOTPLUG_CPU
>  
>  static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
> @@ -481,7 +518,7 @@ void smpboot_thread_init(void)
>  static int _cpu_up(unsigned int cpu, int tasks_frozen)
>  {
>  	struct task_struct *idle;
> -	int ret, nr_calls = 0;
> +	int ret;
>  
>  	cpu_hotplug_begin();
>  
> @@ -496,33 +533,21 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen)
>  		goto out;
>  	}
>  
> +	cpuhp_tasks_frozen = tasks_frozen;
> +
>  	ret = smpboot_create_threads(cpu);
>  	if (ret)
>  		goto out;
>  
> -	cpuhp_tasks_frozen = tasks_frozen;
> -
> -	ret = __cpu_notify(CPU_UP_PREPARE, cpu, -1, &nr_calls);
> -	if (ret) {
> -		nr_calls--;
> -		pr_warn("%s: attempt to bring up CPU %u failed\n",
> -			__func__, cpu);
> -		goto out_notify;
> -	}
> -
> -	/* Arch-specific enabling code. */
> -	ret = __cpu_up(cpu, idle);
> -
> -	if (ret != 0)
> -		goto out_notify;
> -	BUG_ON(!cpu_online(cpu));
> +	ret = notify_prepare(cpu);
> +	if (ret)
> +		goto out;
>  
> -	/* Now call notifier in preparation. */
> -	cpu_notify(CPU_ONLINE, cpu);
> +	ret = bringup_cpu(cpu);
> +	if (ret)
> +		goto out;
>  
> -out_notify:
> -	if (ret != 0)
> -		__cpu_notify(CPU_UP_CANCELED, cpu, nr_calls, NULL);
> +	notify_online(cpu);
>  out:
>  	cpu_hotplug_done();
>  
>