[PATCH v4 03/25] notifier: Add atomic/blocking_notifier_has_unique_priority()

[Dmitry Osipenko]

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.