Re: [PATCH 3/3 RFC] ACPI / hotplug: Use device offline/online for graceful hot-removal

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

On Mon, 2013-04-29 at 14:29 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Modify the generic ACPI hotplug code to be able to check if devices
> scheduled for hot-removal may be gracefully removed from the system
> using the device offline/online mechanism introduced previously.
> 
> Namely, make acpi_scan_hot_remove() which handles device hot-removal
> call device_offline() for all physical companions of the ACPI device
> nodes involved in the operation and check the results.  If any of
> the device_offline() calls fails, the function will not progress to
> the removal phase (which cannot be aborted), unless its (new) force
> argument is set (in case of a failing offline it will put the devices
> offlined by it back online).
> 
> In support of the 'forced' hot-removal, add a new sysfs attribute
> 'force_remove' that will reside in every ACPI hotplug profile
> present under /sys/firmware/acpi/hotplug/.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  Documentation/ABI/testing/sysfs-firmware-acpi |    9 +-
>  drivers/acpi/internal.h                       |    2 
>  drivers/acpi/scan.c                           |   97 ++++++++++++++++++++++++--
>  drivers/acpi/sysfs.c                          |   27 +++++++
>  include/acpi/acpi_bus.h                       |    3 
>  5 files changed, 131 insertions(+), 7 deletions(-)
> 
 :
> Index: linux-pm/drivers/acpi/scan.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/scan.c
> +++ linux-pm/drivers/acpi/scan.c
> @@ -120,7 +120,61 @@ acpi_device_modalias_show(struct device
>  }
>  static DEVICE_ATTR(modalias, 0444, acpi_device_modalias_show, NULL);
>  
> -static int acpi_scan_hot_remove(struct acpi_device *device)
> +static acpi_status acpi_bus_offline_companions(acpi_handle handle, u32 lvl,
> +					       void *data, void **ret_p)
> +{
> +	struct acpi_device *device = NULL;
> +	struct acpi_device_physical_node *pn;
> +	bool force = *((bool *)data);
> +	acpi_status status = AE_OK;
> +
> +	if (acpi_bus_get_device(handle, &device))
> +		return AE_OK;
> +
> +	mutex_lock(&device->physical_node_lock);
> +
> +	list_for_each_entry(pn, &device->physical_node_list, node) {

I do not think physical_node_list is set for ACPI processor devices, so
this code is NOP at this point.  I think properly initializing
physical_node_list for CPU and memblk is one of the key items in this
approach.

> +		int ret;
> +
> +		ret = device_offline(pn->dev);
> +		if (force)
> +			continue;
> +
> +		if (ret < 0) {
> +			status = AE_ERROR;
> +			break;
> +		}
> +		pn->put_online = !ret;
> +	}
> +
> +	mutex_unlock(&device->physical_node_lock);
> +
> +	return status;
> +}
> +
> +static acpi_status acpi_bus_online_companions(acpi_handle handle, u32 lvl,
> +					      void *data, void **ret_p)
> +{
> +	struct acpi_device *device = NULL;
> +	struct acpi_device_physical_node *pn;
> +
> +	if (acpi_bus_get_device(handle, &device))
> +		return AE_OK;
> +
> +	mutex_lock(&device->physical_node_lock);
> +
> +	list_for_each_entry(pn, &device->physical_node_list, node)
> +		if (pn->put_online) {
> +			device_online(pn->dev);
> +			pn->put_online = false;
> +		}
> +
> +	mutex_unlock(&device->physical_node_lock);
> +
> +	return AE_OK;
> +}
> +
> +static int acpi_scan_hot_remove(struct acpi_device *device, bool force)
>  {
>  	acpi_handle handle = device->handle;
>  	acpi_handle not_used;
> @@ -136,10 +190,30 @@ static int acpi_scan_hot_remove(struct a
>  		return -EINVAL;
>  	}
>  
> +	lock_device_offline();
> +
> +	status = acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
> +				     NULL, acpi_bus_offline_companions, &force,
> +				     NULL);
> +	if (ACPI_SUCCESS(status) || force)
> +		status = acpi_bus_offline_companions(handle, 0, &force, NULL);
> +
> +	if (ACPI_FAILURE(status) && !force) {
> +		acpi_bus_online_companions(handle, 0, NULL, NULL);
> +		acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
> +				    acpi_bus_online_companions, NULL, NULL,
> +				    NULL);
> +		unlock_device_offline();

Don't we need put_device(&device->dev) here?

Thanks,
-Toshi


> +		return -EBUSY;
> +	}
> +