linux-kernel - Re: [PATCH 3/4] ACPI / dock: Walk list in reverse order during removal of devices

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Date:	Fri, 28 Jun 2013 13:14:17 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jiang Liu <liuj97@...il.com>,
	"Alexander E. Patrakov" <patrakov@...il.com>
Subject: Re: [PATCH 3/4] ACPI / dock: Walk list in reverse order during
 removal of devices

On Fri, Jun 28, 2013 at 12:47 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> If there are indirect dependencies between devices in a dock
> station's dependent devices list, they may be broken if the devices
> are removed in the same order in which they have been added.
>
> For this reason, make the code in handle_eject_request() walk the
> list of dependent devices in reverse order.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/acpi/dock.c |   45 +++++++++++++++++++++++++++++----------------
>  1 file changed, 29 insertions(+), 16 deletions(-)
>
> Index: linux-pm/drivers/acpi/dock.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/dock.c
> +++ linux-pm/drivers/acpi/dock.c
> @@ -396,9 +396,29 @@ static void dock_remove_acpi_device(acpi
>  }
>
>  /**
> - * hotplug_dock_devices - insert or remove devices on the dock station
> + * hot_remove_dock_devices - Remove dock station devices.
> + * @ds: Dock station.
> + */
> +static void hot_remove_dock_devices(struct dock_station *ds)
> +{
> +       struct dock_dependent_device *dd;
> +
> +       /*
> +        * Walk the list in reverse order so that devices that have been added
> +        * last are removed first (in case there are some indirect dependencies
> +        * between them).
> +        */
> +       list_for_each_entry_reverse(dd, &ds->dependent_devices, list)
> +               dock_hotplug_event(dd, ACPI_NOTIFY_EJECT_REQUEST, false);
> +
> +       list_for_each_entry_reverse(dd, &ds->dependent_devices, list)
> +               dock_remove_acpi_device(dd->handle);
> +}
> +
> +/**
> + * hotplug_dock_devices - Insert devices on a dock station.
>   * @ds: the dock station
> - * @event: either bus check or eject request
> + * @event: either bus check or device check request

Acked-by: Yinghai Lu <yinghai@...nel.org>

>   *
>   * Some devices on the dock station need to have drivers called
>   * to perform hotplug operations after a dock event has occurred.
> @@ -409,24 +429,17 @@ static void hotplug_dock_devices(struct
>  {
>         struct dock_dependent_device *dd;
>
> -       /*
> -        * First call driver specific hotplug functions
> -        */
> +       /* Call driver specific hotplug functions. */
>         list_for_each_entry(dd, &ds->dependent_devices, list)
>                 dock_hotplug_event(dd, event, false);
>
>         /*
> -        * Now make sure that an acpi_device is created for each
> -        * dependent device, or removed if this is an eject request.
> -        * This will cause acpi_drivers to be stopped/started if they
> -        * exist
> +        * Now make sure that an acpi_device is created for each dependent
> +        * device.  That will cause scan handlers to be attached to device
> +        * objects or acpi_drivers to be stopped/started if they are present.
>          */
> -       list_for_each_entry(dd, &ds->dependent_devices, list) {
> -               if (event == ACPI_NOTIFY_EJECT_REQUEST)
> -                       dock_remove_acpi_device(dd->handle);
> -               else
> -                       dock_create_acpi_device(dd->handle);
> -       }
> +       list_for_each_entry(dd, &ds->dependent_devices, list)
> +               dock_create_acpi_device(dd->handle);
>  }
>
>  static void dock_event(struct dock_station *ds, u32 event, int num)
> @@ -699,7 +712,7 @@ static int handle_eject_request(struct d
>          */
>         dock_event(ds, event, UNDOCK_EVENT);
>
> -       hotplug_dock_devices(ds, ACPI_NOTIFY_EJECT_REQUEST);
> +       hot_remove_dock_devices(ds);
>         undock(ds);
>         dock_lock(ds, 0);
>         eject_dock(ds);
>
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