linux-kernel - Re: [PATCH v4 03/25] notifier: Add atomic/blocking_notifier_has_unique

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Message-ID: <218e67e2-1d8c-5727-3862-8884d74aa63e@gmail.com>
Date:   Fri, 10 Dec 2021 23:16:29 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
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Subject: Re: [PATCH v4 03/25] notifier: Add
 atomic/blocking_notifier_has_unique_priority()

10.12.2021 22:33, Dmitry Osipenko пишет:
>> Not really, they only prevent the race from occurring while
>> notifier_has_unique_priority() is running.
>>
>> If anyone depends on this check for correctness, they need to lock the
>> rwsem, do the check, do the thing depending on the check while holding
>> the rwsem and then release the rwsem.  Otherwise it is racy.
>>
> It's fine that it's a bit "racy" since in the context of this series. We
> always do the check after adding new entry, so it's not a problem.
> 
> There are two options:
> 
> 1. Use blocking_notifier_has_unique_priority() like it's done in this
> patchset. Remove it after all drivers are converted to the new API and
> add blocking_notifier_chain_register_unique().
> 
> 2. Add blocking_notifier_chain_register_unique(), but don't let it fail
> the registration of non-unique entries until all drivers are converted
> to the new API.

There is third, perhaps the best option:

3. Add blocking_notifier_chain_register_unique() and fall back to
blocking_notifier_chain_register() if unique fails, do it until all
drivers are converted to the new API.