watchdog: mei: avoid oops in watchdog unregister code path

With commit c7d3df3 "mei: use internal watchdog device registration
tracking" will crash the kernel on shutdown path on systems
where ME watchdog is not present.
Since the watchdog was never initialized in such case
the WDOG_UNREGISTERED bit is never set and the system
crashes on access to uninitialized variables down the path.

To solve the issue we query for NULL on watchdog driver driver_data
to check whether the device is registered. This is handled in the
driver and doesn't depend on watchdog core internals.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Jerry Snitselaar <jerry.snitselaar@oracle.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

diff --git a/drivers/misc/mei/wd.c b/drivers/misc/mei/wd.c
index 636409f9667f397c7ea3ea972fda636cf171e81d..9299a8c29a6fbe4846a06647955ea864ea1921de 100644 (file)
--- a/drivers/misc/mei/wd.c
+++ b/drivers/misc/mei/wd.c
@@ -370,7 +370,7 @@ void mei_watchdog_register(struct mei_device *dev)
 
 void mei_watchdog_unregister(struct mei_device *dev)
 {
-       if (test_bit(WDOG_UNREGISTERED, &amt_wd_dev.status))
+       if (watchdog_get_drvdata(&amt_wd_dev) == NULL)
                return;
 
        watchdog_set_drvdata(&amt_wd_dev, NULL);