Merge tag 'core_core_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull notifier fix from Borislav Petkov:
 "Return an error when a notifier callback has been registered already"

* tag 'core_core_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  notifier: Return an error when a callback has already been registered

kernel/notifier.c

@@ -20,12 +20,13 @@ BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);
  */
 
 static int notifier_chain_register(struct notifier_block **nl,
-		struct notifier_block *n)
+				   struct notifier_block *n)
 {
 	while ((*nl) != NULL) {
 		if (unlikely((*nl) == n)) {
-			WARN(1, "double register detected");
-			return 0;
+			WARN(1, "notifier callback %ps already registered",
+			     n->notifier_call);
+			return -EEXIST;
 		}
 		if (n->priority > (*nl)->priority)
 			break;
@@ -134,7 +135,7 @@ static int notifier_call_chain_robust(struct notifier_block **nl,
  *
  *	Adds a notifier to an atomic notifier chain.
  *
- *	Currently always returns zero.
+ *	Returns 0 on success, %-EEXIST on error.
  */
 int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 		struct notifier_block *n)
@@ -216,7 +217,7 @@ NOKPROBE_SYMBOL(atomic_notifier_call_chain);
  *	Adds a notifier to a blocking notifier chain.
  *	Must be called in process context.
  *
- *	Currently always returns zero.
+ *	Returns 0 on success, %-EEXIST on error.
  */
 int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 		struct notifier_block *n)
@@ -335,7 +336,7 @@ EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
  *	Adds a notifier to a raw notifier chain.
  *	All locking must be provided by the caller.
  *
- *	Currently always returns zero.
+ *	Returns 0 on success, %-EEXIST on error.
  */
 int raw_notifier_chain_register(struct raw_notifier_head *nh,
 		struct notifier_block *n)
@@ -406,7 +407,7 @@ EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
  *	Adds a notifier to an SRCU notifier chain.
  *	Must be called in process context.
  *
- *	Currently always returns zero.
+ *	Returns 0 on success, %-EEXIST on error.
  */
 int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 		struct notifier_block *n)