Re: [PATCH 2/3 RFC] Driver core: Use generic offline/online for CPU offline/online

[Toshi Kani <toshi.kani@hp.com>]

On Mon, 2013-04-29 at 14:28 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Rework the CPU hotplug code in drivers/base/cpu.c to use the
> generic offline/online support introduced previously instead of
> its own CPU-specific code.
> 
> For this purpose, modify cpu_subsys to provide offline and online
> callbacks for CONFIG_HOTPLUG_CPU set and remove the code handling
> the CPU-specific 'online' sysfs attribute.
> 
> This modification is not supposed to change the user-observable
> behavior of the kernel (i.e. the 'online' attribute will be present
> in exactly the same place in sysfs and should trigger exactly the
> same actions as before).
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/base/cpu.c |   62 ++++++++++++-----------------------------------------
>  1 file changed, 15 insertions(+), 47 deletions(-)
> 
> Index: linux-pm/drivers/base/cpu.c
> ===================================================================
> --- linux-pm.orig/drivers/base/cpu.c
> +++ linux-pm/drivers/base/cpu.c
> @@ -16,66 +16,25 @@
>  
>  #include "base.h"
>  
> -struct bus_type cpu_subsys = {
> -	.name = "cpu",
> -	.dev_name = "cpu",
> -};
> -EXPORT_SYMBOL_GPL(cpu_subsys);
> -
>  static DEFINE_PER_CPU(struct device *, cpu_sys_devices);
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> -static ssize_t show_online(struct device *dev,
> -			   struct device_attribute *attr,
> -			   char *buf)
> +static int cpu_subsys_online(struct device *dev)
>  {
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -
> -	return sprintf(buf, "%u\n", !!cpu_online(cpu->dev.id));
> +	return cpu_up(dev->id);
>  }
>  
> -static ssize_t __ref store_online(struct device *dev,
> -				  struct device_attribute *attr,
> -				  const char *buf, size_t count)
> +static int cpu_subsys_offline(struct device *dev)
>  {
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -	ssize_t ret;
> -
> -	cpu_hotplug_driver_lock();

By replacing cpu_hotplug_driver_lock() with lock_device_offline() in
patch 1/3, it no longer protects from other places that still use
cpu_hotplug_device_lock(), such as save_mc_for_early().

Thanks,
-Toshi


> -	switch (buf[0]) {
> -	case '0':
> -		ret = cpu_down(cpu->dev.id);
> -		if (!ret)
> -			kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
> -		break;
> -	case '1':
> -		ret = cpu_up(cpu->dev.id);
> -		if (!ret)
> -			kobject_uevent(&dev->kobj, KOBJ_ONLINE);
> -		break;
> -	default:
> -		ret = -EINVAL;
> -	}
> -	cpu_hotplug_driver_unlock();
> -
> -	if (ret >= 0)
> -		ret = count;
> -	return ret;
> +	return cpu_down(dev->id);
>  }
> -static DEVICE_ATTR(online, 0644, show_online, store_online);