[PATCH] ACPI / dock: Take ACPI scan lock in write_undock()

["Rafael J. Wysocki" <rjw@sisk.pl>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Since commit 3757b94 (ACPI / hotplug: Fix concurrency issues and
memory leaks) acpi_bus_scan() and acpi_bus_trim() must always be
called under acpi_scan_lock, but currently the following scenario
violating that requirement is possible:

 write_undock()
  handle_eject_request()
   hotplug_dock_devices()
    dock_remove_acpi_device()
     acpi_bus_trim()

Fix that by making write_undock() acquire acpi_scan_lock before
calling handle_eject_request() as appropriate (begin_undock() is
under the lock too in analogy with acpi_dock_deferred_cb()).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 3.9+ <stable@vger.kernel.org>
---
 drivers/acpi/dock.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-pm/drivers/acpi/dock.c
===================================================================
--- linux-pm.orig/drivers/acpi/dock.c
+++ linux-pm/drivers/acpi/dock.c
@@ -868,8 +868,10 @@ static ssize_t write_undock(struct devic
 	if (!count)
 		return -EINVAL;
 
+	acpi_scan_lock_acquire();
 	begin_undock(dock_station);
 	ret = handle_eject_request(dock_station, ACPI_NOTIFY_EJECT_REQUEST);
+	acpi_scan_lock_release();
 	return ret ? ret: count;
 }
 static DEVICE_ATTR(undock, S_IWUSR, NULL, write_undock);