uwb: properly check kthread_run return value

uwbd_start() calls kthread_run() and checks that the return value is
not NULL. But the return value is not NULL in case kthread_run() fails,
it takes the form of ERR_PTR(-EINTR).

Use IS_ERR() instead.

Also add a check to uwbd_stop().
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/uwb/uwbd.c

@@ -302,17 +302,21 @@ static int uwbd(void *param)
 /** Start the UWB daemon */
 void uwbd_start(struct uwb_rc *rc)
 {
-	rc->uwbd.task = kthread_run(uwbd, rc, "uwbd");
-	if (rc->uwbd.task == NULL)
+	struct task_struct *task = kthread_run(uwbd, rc, "uwbd");
+	if (IS_ERR(task)) {
+		rc->uwbd.task = NULL;
 		printk(KERN_ERR "UWB: Cannot start management daemon; "
 		       "UWB won't work\n");
-	else
+	} else {
+		rc->uwbd.task = task;
 		rc->uwbd.pid = rc->uwbd.task->pid;
+	}
 }
 
 /* Stop the UWB daemon and free any unprocessed events */
 void uwbd_stop(struct uwb_rc *rc)
 {
+	if (rc->uwbd.task)
 		kthread_stop(rc->uwbd.task);
 	uwbd_flush(rc);
 }