Message-ID: <20130209003900.GX2666@linux.vnet.ibm.com>
Date:	Fri, 8 Feb 2013 16:39:00 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Arjan van de Veen <arjan@...radead.org>,
	Paul Turner <pjt@...gle.com>,
	Richard Weinberger <rw@...utronix.de>,
	Magnus Damm <magnus.damm@...il.com>
Subject: Re: [patch 03/40] stop_machine: Use smpboot threads

On Thu, Jan 31, 2013 at 12:11:14PM -0000, Thomas Gleixner wrote:
> Use the smpboot thread infrastructure. Mark the stopper thread
> selfparking and park it after it has finished the take_cpu_down()
> work.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

One grammar nit, other than that:

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
>  kernel/cpu.c          |    2 
>  kernel/stop_machine.c |  134 ++++++++++++++++++--------------------------------
>  2 files changed, 51 insertions(+), 85 deletions(-)
> 
> Index: linux-2.6/kernel/cpu.c
> ===================================================================
> --- linux-2.6.orig/kernel/cpu.c
> +++ linux-2.6/kernel/cpu.c
> @@ -254,6 +254,8 @@ static int __ref take_cpu_down(void *_pa
>  		return err;
> 
>  	cpu_notify(CPU_DYING | param->mod, param->hcpu);
> +	/* Park the stopper thread */
> +	kthread_park(current);
>  	return 0;
>  }
> 
> Index: linux-2.6/kernel/stop_machine.c
> ===================================================================
> --- linux-2.6.orig/kernel/stop_machine.c
> +++ linux-2.6/kernel/stop_machine.c
> @@ -18,7 +18,7 @@
>  #include <linux/stop_machine.h>
>  #include <linux/interrupt.h>
>  #include <linux/kallsyms.h>
> -
> +#include <linux/smpboot.h>
>  #include <linux/atomic.h>
> 
>  /*
> @@ -245,20 +245,25 @@ int try_stop_cpus(const struct cpumask *
>  	return ret;
>  }
> 
> -static int cpu_stopper_thread(void *data)
> +static int cpu_stop_should_run(unsigned int cpu)
> +{
> +	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> +	unsigned long flags;
> +	int run;
> +
> +	spin_lock_irqsave(&stopper->lock, flags);
> +	run = !list_empty(&stopper->works);
> +	spin_unlock_irqrestore(&stopper->lock, flags);
> +	return run;
> +}
> +
> +static void cpu_stopper_thread(unsigned int cpu)
>  {
> -	struct cpu_stopper *stopper = data;
> +	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
>  	struct cpu_stop_work *work;
>  	int ret;
> 
>  repeat:
> -	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
> -
> -	if (kthread_should_stop()) {
> -		__set_current_state(TASK_RUNNING);
> -		return 0;
> -	}
> -
>  	work = NULL;
>  	spin_lock_irq(&stopper->lock);
>  	if (!list_empty(&stopper->works)) {
> @@ -274,8 +279,6 @@ repeat:
>  		struct cpu_stop_done *done = work->done;
>  		char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
> 
> -		__set_current_state(TASK_RUNNING);
> -
>  		/* cpu stop callbacks are not allowed to sleep */
>  		preempt_disable();
> 
> @@ -291,87 +294,55 @@ repeat:
>  					  ksym_buf), arg);
> 
>  		cpu_stop_signal_done(done, true);
> -	} else
> -		schedule();
> -
> -	goto repeat;
> +		goto repeat;
> +	}
>  }
> 
>  extern void sched_set_stop_task(int cpu, struct task_struct *stop);
> 
> -/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
> -static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
> -					   unsigned long action, void *hcpu)
> +static void cpu_stop_create(unsigned int cpu)
> +{
> +	sched_set_stop_task(cpu, per_cpu(cpu_stopper_task, cpu));
> +}
> +
> +static void cpu_stop_park(unsigned int cpu)
>  {
> -	unsigned int cpu = (unsigned long)hcpu;
>  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> -	struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
> +	struct cpu_stop_work *work;
> +	unsigned long flags;
> 
> -	switch (action & ~CPU_TASKS_FROZEN) {
> -	case CPU_UP_PREPARE:
> -		BUG_ON(p || stopper->enabled || !list_empty(&stopper->works));
> -		p = kthread_create_on_node(cpu_stopper_thread,
> -					   stopper,
> -					   cpu_to_node(cpu),
> -					   "migration/%d", cpu);
> -		if (IS_ERR(p))
> -			return notifier_from_errno(PTR_ERR(p));
> -		get_task_struct(p);
> -		kthread_bind(p, cpu);
> -		sched_set_stop_task(cpu, p);
> -		per_cpu(cpu_stopper_task, cpu) = p;
> -		break;
> +	/* drain remaining works */

s/works/work/

> +	spin_lock_irqsave(&stopper->lock, flags);
> +	list_for_each_entry(work, &stopper->works, list)
> +		cpu_stop_signal_done(work->done, false);
> +	stopper->enabled = false;
> +	spin_unlock_irqrestore(&stopper->lock, flags);
> +}
> 
> -	case CPU_ONLINE:
> -		/* strictly unnecessary, as first user will wake it */
> -		wake_up_process(p);
> -		/* mark enabled */
> -		spin_lock_irq(&stopper->lock);
> -		stopper->enabled = true;
> -		spin_unlock_irq(&stopper->lock);
> -		break;
> -
> -#ifdef CONFIG_HOTPLUG_CPU
> -	case CPU_UP_CANCELED:
> -	case CPU_POST_DEAD:
> -	{
> -		struct cpu_stop_work *work;
> -
> -		sched_set_stop_task(cpu, NULL);
> -		/* kill the stopper */
> -		kthread_stop(p);
> -		/* drain remaining works */
> -		spin_lock_irq(&stopper->lock);
> -		list_for_each_entry(work, &stopper->works, list)
> -			cpu_stop_signal_done(work->done, false);
> -		stopper->enabled = false;
> -		spin_unlock_irq(&stopper->lock);
> -		/* release the stopper */
> -		put_task_struct(p);
> -		per_cpu(cpu_stopper_task, cpu) = NULL;
> -		break;
> -	}
> -#endif
> -	}
> +static void cpu_stop_unpark(unsigned int cpu)
> +{
> +	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> 
> -	return NOTIFY_OK;
> +	spin_lock_irq(&stopper->lock);
> +	stopper->enabled = true;
> +	spin_unlock_irq(&stopper->lock);
>  }
> 
> -/*
> - * Give it a higher priority so that cpu stopper is available to other
> - * cpu notifiers.  It currently shares the same priority as sched
> - * migration_notifier.
> - */
> -static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
> -	.notifier_call	= cpu_stop_cpu_callback,
> -	.priority	= 10,
> +static struct smp_hotplug_thread cpu_stop_threads = {
> +	.store			= &cpu_stopper_task,
> +	.thread_should_run	= cpu_stop_should_run,
> +	.thread_fn		= cpu_stopper_thread,
> +	.thread_comm		= "migration/%u",
> +	.create			= cpu_stop_create,
> +	.setup			= cpu_stop_unpark,
> +	.park			= cpu_stop_park,
> +	.unpark			= cpu_stop_unpark,
> +	.selfparking		= true,
>  };
> 
>  static int __init cpu_stop_init(void)
>  {
> -	void *bcpu = (void *)(long)smp_processor_id();
>  	unsigned int cpu;
> -	int err;
> 
>  	for_each_possible_cpu(cpu) {
>  		struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> @@ -380,15 +351,8 @@ static int __init cpu_stop_init(void)
>  		INIT_LIST_HEAD(&stopper->works);
>  	}
> 
> -	/* start one for the boot cpu */
> -	err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
> -				    bcpu);
> -	BUG_ON(err != NOTIFY_OK);
> -	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
> -	register_cpu_notifier(&cpu_stop_cpu_notifier);
> -
> +	BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
>  	stop_machine_initialized = true;
> -
>  	return 0;
>  }
>  early_initcall(cpu_stop_init);
> 
> 

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