Re: [PATCH 3/3] ACPI / dock / PCI: Synchronous handling of dock events for PCI devices

[Yinghai Lu <yinghai@kernel.org>]

On Sat, Jun 22, 2013 at 2:25 PM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> To resolve that deadlock use the observation that
> unregister_hotplug_dock_device() won't need to acquire hp_lock
> if PCI bridges the devices on the dock station depend on are
> prevented from being removed prematurely while the first loop in
> hotplug_dock_devices() is in progress.
>
> To make that possible, introduce a mechanism by which the callers of
> register_hotplug_dock_device() can provide "init" and "release"
> routines that will be executed, respectively, after the addition
> and removal of the physical device object associated with the
> given ACPI device handle.  Make acpiphp use two new functions,
> acpiphp_dock_init() and acpiphp_dock_release(), respectively,
> calling get_bridge() and put_bridge() on the PCI bridge holding the
> given device, respectively, for this purpose.
>
> In addition to that, remove the dock station's list of
> "hotplug devices" and make the dock code always walk the whole list
> of "dependent devices" instead in such a way that the loops in
> hotplug_dock_devices() and dock_event() (replacing the loops over
> "hotplug devices") will take references to the list entries that
> register_hotplug_dock_device() has been called for.  That prevents
> the "release" routines associated with those entries from being
> called while the given entry is being processed and for PCI
> devices this means that their bridges won't be removed (by a
> concurrent thread) while hotplug_event_func() handling them is
> being executed.
..
> -static void
> -dock_del_hotplug_device(struct dock_station *ds,
> -                       struct dock_dependent_device *dd)
> +static void dock_release_hotplug(struct dock_dependent_device *dd)
>  {
> -       mutex_lock(&ds->hp_lock);
> -       list_del(&dd->hotplug_list);
> -       mutex_unlock(&ds->hp_lock);
> +       void (*release)(void *) = NULL;
> +       void *context = NULL;
> +
> +       mutex_lock(&hotplug_lock);
> +
> +       if (dd->hp_context && !--dd->hp_refcount) {
> +               dd->hp_ops = NULL;
> +               context = dd->hp_context;
> +               dd->hp_context = NULL;
> +               release = dd->hp_release;
> +               dd->hp_release = NULL;
> +       }
> +
> +       if (release && context)
> +               release(context);
> +
> +       mutex_unlock(&hotplug_lock);
> +}
> +
> +static void dock_hotplug_event(struct dock_dependent_device *dd, u32 event,
> +                              bool uevent)
> +{
> +       acpi_notify_handler cb = NULL;
> +       bool run = false;
> +
> +       mutex_lock(&hotplug_lock);
> +
> +       if (dd->hp_context) {
> +               run = true;
> +               dd->hp_refcount++;
> +               if (dd->hp_ops)
> +                       cb = uevent ? dd->hp_ops->uevent : dd->hp_ops->handler;
> +       }
> +
> +       mutex_unlock(&hotplug_lock);
> +
> +       if (!run)
> +               return;
> +
> +       if (cb)
> +               cb(dd->handle, event, dd->hp_context);
> +
> +       dock_release_hotplug(dd);

during DOCKING, dock_release_hotplug get called too?

Yinghai