Re: [PATCH 25/27] locking/lockdep: Add support for dynamic keys

[Peter Zijlstra]

On Wed, Nov 28, 2018 at 03:43:23PM -0800, Bart Van Assche wrote:
> A shortcoming of the current lockdep implementation is that it requires
> lock keys to be allocated statically. That forces certain lock objects
> to share lock keys. Since lock dependency analysis groups lock objects
> per key sharing lock keys can cause false positive lockdep reports.
> Make it possible to avoid such false positive reports by allowing lock
> keys to be allocated dynamically. Require that dynamically allocated
> lock keys are registered before use by calling lockdep_register_key().
> Complain about attempts to register the same lock key pointer twice
> without calling lockdep_unregister_key() between successive
> registration calls.

>  struct lock_class_key {
> +	struct hlist_node		hash_entry;
>  	struct lockdep_subclass_key	subkeys[MAX_LOCKDEP_SUBCLASSES];
>  };

That hash_entry is purely for that double-register warning, right? I
wonder if we can do that differently; by always doing
register_lock_class(), and checking that state.