10.12.2021 21:32, Rafael J. Wysocki пишет:

On Fri, Nov 26, 2021 at 7:02 PM Dmitry Osipenko [off-list ref] wrote:

quoted

Emit warning if unregister_restart_handler() fails since it never should
fail. This will ease further API development by catching mistakes early.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 kernel/reboot.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index e6659ae329f1..f0e7b9c13f6b 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c

@@ -210,7 +210,7 @@ EXPORT_SYMBOL(register_restart_handler);
  */
 int unregister_restart_handler(struct notifier_block *nb)
 {
-       return atomic_notifier_chain_unregister(&restart_handler_list, nb);
+       return WARN_ON(atomic_notifier_chain_unregister(&restart_handler_list, nb));

The only reason why it can fail is if the object pointed to by nb is
not in the chain.

I had exactly this case where object wasn't in the chain due to a bug
and this warning was very helpful.

 Why WARN() about this?  And what about systems with
panic_on_warn set?

That warning condition will never happen normally, only when something
is seriously wrong.

Those systems with panic_on_warn will get what was they asked for.