From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Yinghai Lu <yinghai@kernel.org>
Cc: ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Alexander E . Patrakov" <patrakov@gmail.com>,
        Jiang Liu <jiang.liu@huawei.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Yijing Wang <wangyijing@huawei.com>, Jiang Liu <liuj97@gmail.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] ACPI / dock / PCI: Synchronous handling of dock events for PCI devices
Date: Sun, 23 Jun 2013 11:59:41 +0200
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On Saturday, June 22, 2013 05:22:20 PM Yinghai Lu wrote:
> 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?

Yes, we need to drop down the refcount we've just bumped up.

Thanks,
Rafael

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