From 953b9dd7725bad55a922a35e75bff7bebf7b9978 Mon Sep 17 00:00:00 2001
From: Wolfram Sang <wsa+renesas@sang-engineering.com>
Date: Tue, 28 Aug 2018 12:13:47 +0200
Subject: [PATCH] watchdog: core: fix null pointer dereference when releasing cdev
Git-commit: 953b9dd7725bad55a922a35e75bff7bebf7b9978
Patch-mainline: v4.20-rc1
References: bsc#1051510

watchdog_stop() calls watchdog_update_worker() which needs a valid
wdd->wd_data pointer. So, when unregistering the cdev, clear the
pointers after we call watchdog_stop(), not before.

Fixes: bb292ac1c602 ("watchdog: Introduce watchdog_stop_on_unregister helper")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/watchdog/watchdog_dev.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -984,16 +984,16 @@ static void watchdog_cdev_unregister(str
 		old_wd_data = NULL;
 	}
 
-	mutex_lock(&wd_data->lock);
-	wd_data->wdd = NULL;
-	wdd->wd_data = NULL;
-	mutex_unlock(&wd_data->lock);
-
 	if (watchdog_active(wdd) &&
 	    test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
 		watchdog_stop(wdd);
 	}
 
+	mutex_lock(&wd_data->lock);
+	wd_data->wdd = NULL;
+	wdd->wd_data = NULL;
+	mutex_unlock(&wd_data->lock);
+
 	cancel_delayed_work_sync(&wd_data->work);
 
 	kref_put(&wd_data->kref, watchdog_core_data_release);