Re: [patch 04/40] cpu: Restructure FROZEN state handling

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, Jan 31, 2013 at 12:11:15PM -0000, Thomas Gleixner wrote:
> There are only a few callbacks which really care about FROZEN
> vs. !FROZEN. No need to have extra states for this. 
> 
> Publish the frozen state in an extra variable which is updated under
> the hotplug lock and let the users interested deal with it w/o
> imposing that extra state checks on everyone.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Getting rid of all the _FROZEN variants of the notifier actions would
be good!

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

> ---
>  kernel/cpu.c |   66 ++++++++++++++++++++++++-----------------------------------
>  1 file changed, 27 insertions(+), 39 deletions(-)
> 
> Index: linux-2.6/kernel/cpu.c
> ===================================================================
> --- linux-2.6.orig/kernel/cpu.c
> +++ linux-2.6/kernel/cpu.c
> @@ -25,6 +25,7 @@
>  #ifdef CONFIG_SMP
>  /* Serializes the updates to cpu_online_mask, cpu_present_mask */
>  static DEFINE_MUTEX(cpu_add_remove_lock);
> +static bool cpuhp_tasks_frozen;
> 
>  /*
>   * The following two API's must be used when attempting
> @@ -148,27 +149,30 @@ int __ref register_cpu_notifier(struct n
>  	return ret;
>  }
> 
> -static int __cpu_notify(unsigned long val, void *v, int nr_to_call,
> +static int __cpu_notify(unsigned long val, unsigned int cpu, int nr_to_call,
>  			int *nr_calls)
>  {
> +	unsigned long mod = cpuhp_tasks_frozen ? CPU_TASKS_FROZEN : 0;
> +	void *hcpu = (void *)(long)cpu;
> +
>  	int ret;
> 
> -	ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call,
> +	ret = __raw_notifier_call_chain(&cpu_chain, val | mod, hcpu, nr_to_call,
>  					nr_calls);
> 
>  	return notifier_to_errno(ret);
>  }
> 
> -static int cpu_notify(unsigned long val, void *v)
> +static int cpu_notify(unsigned long val, unsigned int cpu)
>  {
> -	return __cpu_notify(val, v, -1, NULL);
> +	return __cpu_notify(val, cpu, -1, NULL);
>  }
> 
>  #ifdef CONFIG_HOTPLUG_CPU
> 
> -static void cpu_notify_nofail(unsigned long val, void *v)
> +static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
>  {
> -	BUG_ON(cpu_notify(val, v));
> +	BUG_ON(cpu_notify(val, cpu));
>  }
>  EXPORT_SYMBOL(register_cpu_notifier);
> 
> @@ -237,23 +241,17 @@ static inline void check_for_tasks(int c
>  	write_unlock_irq(&tasklist_lock);
>  }
> 
> -struct take_cpu_down_param {
> -	unsigned long mod;
> -	void *hcpu;
> -};
> -
>  /* Take this CPU down. */
>  static int __ref take_cpu_down(void *_param)
>  {
> -	struct take_cpu_down_param *param = _param;
> -	int err;
> +	int err, cpu = smp_processor_id();
> 
>  	/* Ensure this CPU doesn't handle any more interrupts. */
>  	err = __cpu_disable();
>  	if (err < 0)
>  		return err;
> 
> -	cpu_notify(CPU_DYING | param->mod, param->hcpu);
> +	cpu_notify(CPU_DYING, cpu);
>  	/* Park the stopper thread */
>  	kthread_park(current);
>  	return 0;
> @@ -263,12 +261,6 @@ static int __ref take_cpu_down(void *_pa
>  static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
>  {
>  	int err, nr_calls = 0;
> -	void *hcpu = (void *)(long)cpu;
> -	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
> -	struct take_cpu_down_param tcd_param = {
> -		.mod = mod,
> -		.hcpu = hcpu,
> -	};
> 
>  	if (num_online_cpus() == 1)
>  		return -EBUSY;
> @@ -278,21 +270,23 @@ static int __ref _cpu_down(unsigned int 
> 
>  	cpu_hotplug_begin();
> 
> -	err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
> +	cpuhp_tasks_frozen = tasks_frozen;
> +
> +	err = __cpu_notify(CPU_DOWN_PREPARE, cpu, -1, &nr_calls);
>  	if (err) {
>  		nr_calls--;
> -		__cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
> +		__cpu_notify(CPU_DOWN_FAILED, cpu, nr_calls, NULL);
>  		printk("%s: attempt to take down CPU %u failed\n",
>  				__func__, cpu);
>  		goto out_release;
>  	}
>  	smpboot_park_threads(cpu);
> 
> -	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> +	err = __stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
>  	if (err) {
>  		/* CPU didn't die: tell everyone.  Can't complain. */
>  		smpboot_unpark_threads(cpu);
> -		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> +		cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
>  		goto out_release;
>  	}
>  	BUG_ON(cpu_online(cpu));
> @@ -311,14 +305,14 @@ static int __ref _cpu_down(unsigned int 
>  	__cpu_die(cpu);
> 
>  	/* CPU is completely dead: tell everyone.  Too late to complain. */
> -	cpu_notify_nofail(CPU_DEAD | mod, hcpu);
> +	cpu_notify_nofail(CPU_DEAD, cpu);
> 
>  	check_for_tasks(cpu);
> 
>  out_release:
>  	cpu_hotplug_done();
>  	if (!err)
> -		cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
> +		cpu_notify_nofail(CPU_POST_DEAD, cpu);
>  	return err;
>  }
> 
> @@ -345,10 +339,8 @@ EXPORT_SYMBOL(cpu_down);
>  /* Requires cpu_add_remove_lock to be held */
>  static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
>  {
> -	int ret, nr_calls = 0;
> -	void *hcpu = (void *)(long)cpu;
> -	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
>  	struct task_struct *idle;
> +	int ret, nr_calls = 0;
> 
>  	cpu_hotplug_begin();
> 
> @@ -367,7 +359,9 @@ static int __cpuinit _cpu_up(unsigned in
>  	if (ret)
>  		goto out;
> 
> -	ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
> +	cpuhp_tasks_frozen = tasks_frozen;
> +
> +	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",
> @@ -385,11 +379,11 @@ static int __cpuinit _cpu_up(unsigned in
>  	smpboot_unpark_threads(cpu);
> 
>  	/* Now call notifier in preparation. */
> -	cpu_notify(CPU_ONLINE | mod, hcpu);
> +	cpu_notify(CPU_ONLINE, cpu);
> 
>  out_notify:
>  	if (ret != 0)
> -		__cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
> +		__cpu_notify(CPU_UP_CANCELED, cpu, nr_calls, NULL);
>  out:
>  	cpu_hotplug_done();
> 
> @@ -627,13 +621,7 @@ core_initcall(cpu_hotplug_pm_sync_init);
>   */
>  void __cpuinit notify_cpu_starting(unsigned int cpu)
>  {
> -	unsigned long val = CPU_STARTING;
> -
> -#ifdef CONFIG_PM_SLEEP_SMP
> -	if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
> -		val = CPU_STARTING_FROZEN;
> -#endif /* CONFIG_PM_SLEEP_SMP */
> -	cpu_notify(val, (void *)(long)cpu);
> +	cpu_notify(CPU_STARTING, cpu);
>  }
> 
>  #endif /* CONFIG_SMP */
> 
>