[DLM] fix oops in kref_put when removing a lockspace

Now that the lockspace struct is freed when the last sysfs object is released
this patch prevents use of that lockspace by sysfs. We attempt to re-get the
lockspace from the lockspace list and fail the request if it has been removed.
Signed-Off-By: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/dlm/lockspace.c

@@ -43,6 +43,10 @@ static ssize_t dlm_control_store(struct dlm_ls *ls, const char *buf, size_t len)
 	ssize_t ret = len;
 	int n = simple_strtol(buf, NULL, 0);
 
+	ls = dlm_find_lockspace_local(ls->ls_local_handle);
+	if (!ls)
+		return -EINVAL;
+
 	switch (n) {
 	case 0:
 		dlm_ls_stop(ls);
@@ -53,6 +57,7 @@ static ssize_t dlm_control_store(struct dlm_ls *ls, const char *buf, size_t len)
 	default:
 		ret = -EINVAL;
 	}
+	dlm_put_lockspace(ls);
 	return ret;
 }