ACPI / hotplug: Fix potential race in acpi_bus_notify()

There is a slight possibility for the ACPI device object pointed to
by adev in acpi_hotplug_notify_cb() to become invalid between the
acpi_bus_get_device() that it comes from and the subsequent dereference
of that pointer under get_device().  Namely, if acpi_scan_drop_device()
runs in parallel with acpi_hotplug_notify_cb(), acpi_device_del_work_fn()
queued up by it may delete the device object in question right after
a successful execution of acpi_bus_get_device() in acpi_bus_notify().

An analogous problem is present in acpi_bus_notify() where the device
pointer coming from acpi_bus_get_device() may become invalid before
it subsequent dereference in the "if" block.

To prevent that from happening, introduce a new function,
acpi_bus_get_acpi_device(), working analogously to acpi_bus_get_device()
except that it will grab a reference to the ACPI device object returned
by it and it will do that under the ACPICA's namespace mutex.  Then,
make both acpi_hotplug_notify_cb() and acpi_bus_notify() use
acpi_bus_get_acpi_device() instead of acpi_bus_get_device() so as to
ensure that the pointers used by them will not become stale at one
point.

In addition to that, introduce acpi_bus_put_acpi_device() as a wrapper
around put_device() to be used along with acpi_bus_get_acpi_device()
and make the (new) users of the latter use acpi_bus_put_acpi_device()
too.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index fcb59c2..c323777 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -340,7 +340,7 @@ static void acpi_bus_osc_support(void)
  */
 static void acpi_bus_notify(acpi_handle handle, u32 type, void *data)
 {
-	struct acpi_device *device = NULL;
+	struct acpi_device *device;
 	struct acpi_driver *driver;
 
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Notification %#02x to handle %p\n",
@@ -387,12 +387,14 @@ static void acpi_bus_notify(acpi_handle handle, u32 type, void *data)
 		break;
 	}
 
-	acpi_bus_get_device(handle, &device);
+	device = acpi_bus_get_acpi_device(handle);
 	if (device) {
 		driver = device->driver;
 		if (driver && driver->ops.notify &&
 		    (driver->flags & ACPI_DRIVER_ALL_NOTIFY_EVENTS))
 			driver->ops.notify(device, type);
+
+		acpi_bus_put_acpi_device(device);
 	}
 }