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

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Date:   Sun, 28 Nov 2021 01:28:40 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
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Subject: Re: [PATCH v4 05/25] reboot: Warn if restart handler has duplicated
 priority

On Fri, Nov 26, 2021 at 09:00:41PM +0300, Dmitry Osipenko wrote:
> 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.

The patch doesn't ensure the property that there are no duplicated-priority
entries on the chain.

I'd rather see a atomic_notifier_chain_register_unique() that returns
-EBUSY or something istead of adding an entry with duplicate priority.
That way it would need only one list traversal unless you want to
register the duplicate anyway (then you would call the older
atomic_notifier_chain_register() after reporting the error).

(Or you could return > 0 when a duplicate is registered in
atomic_notifier_chain_register() if the callers are prepared
for that. I don't really like this way, though.)

Best Regards
Michał Mirosław