Subject: [PATCH v5 03/21] reboot: Print error message if restart handler has duplicated priority

From: Dmitry Osipenko <[email-masked]>
Date: Mon, 13 Dec 2021 00:02:51 +0300

Add sanity check which ensures that there are no two restart handlers
registered using the same priority. This requirement will become mandatory
once all drivers will be converted to the new API and such errors will be
fixed.

Signed-off-by: Dmitry Osipenko <[email-masked]>
---
 kernel/reboot.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index 6bcc5d6a6572..35f0cde641c1 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -182,6 +182,21 @@ static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
  */
 int register_restart_handler(struct notifier_block *nb)
 {
+	int ret;
+
+	ret = atomic_notifier_chain_register_unique_prio(&restart_handler_list, nb);
+	if (ret != -EBUSY)
+		return ret;
+
+	/*
+	 * Handler must have unique priority. Otherwise call order is
+	 * determined by registration order, which is unreliable.
+	 *
+	 * This requirement will become mandatory once all drivers
+	 * will be converted to use new sys-off API.
+	 */
+	pr_err("failed to register restart handler using unique priority\n");
+
 	return atomic_notifier_chain_register(&restart_handler_list, nb);
 }
 EXPORT_SYMBOL(register_restart_handler);
-- 
2.33.1