[PATCH v4 05/25] reboot: Warn if restart handler has duplicated priority

[Dmitry Osipenko]

Add sanity check which ensures that there are no two restart handlers
registered with the same priority. Normally it's a direct sign of a
problem if two handlers use the same priority.

Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
---
 kernel/reboot.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index 6bcc5d6a6572..e6659ae329f1 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -182,7 +182,20 @@ static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
  */
 int register_restart_handler(struct notifier_block *nb)
 {
-	return atomic_notifier_chain_register(&restart_handler_list, nb);
+	int ret;
+
+	ret = atomic_notifier_chain_register(&restart_handler_list, nb);
+	if (ret)
+		return ret;
+
+	/*
+	 * Handler must have unique priority. Otherwise call order is
+	 * determined by registration order, which is unreliable.
+	 */
+	WARN(!atomic_notifier_has_unique_priority(&restart_handler_list, nb),
+	     "restart handler must have unique priority\n");
+
+	return 0;
 }
 EXPORT_SYMBOL(register_restart_handler);
 
-- 
2.33.1