Re: [PATCH 1/2] locking/lockdep: Cleanup reinit_class()

[Peter Zijlstra]

On Thu, Feb 10, 2022 at 10:55:25PM -0500, Waiman Long wrote:
> Replace the duplicated WARN_ON_ONCE() tests in reinit_class() with
> BUILD_BUG_ON().
> 
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> ---
>  include/linux/lockdep_types.h | 4 ++++
>  kernel/locking/lockdep.c      | 6 +++---
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
> index d22430840b53..446d981ae3a2 100644
> --- a/include/linux/lockdep_types.h
> +++ b/include/linux/lockdep_types.h
> @@ -108,6 +108,10 @@ struct lock_class {
>  	 */
>  	struct list_head		locks_after, locks_before;
>  
> +	/*
> +	 * All the fields that require re-initialization after being zapped
> +	 * must be put after "key".
> +	 */
>  	const struct lockdep_subclass_key *key;
>  	unsigned int			subclass;
>  	unsigned int			dep_gen_id;
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index d4252b5c9863..77bbe557d48b 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -6015,10 +6015,10 @@ static void reinit_class(struct lock_class *class)
>  	WARN_ON_ONCE(!class->lock_entry.next);
>  	WARN_ON_ONCE(!list_empty(&class->locks_after));
>  	WARN_ON_ONCE(!list_empty(&class->locks_before));
> +	BUILD_BUG_ON(offsetof(struct lock_class, lock_entry) > offset);
> +	BUILD_BUG_ON(offsetof(struct lock_class, locks_after) > offset);
> +	BUILD_BUG_ON(offsetof(struct lock_class, locks_before) > offset);
>  	memset(p + offset, 0, sizeof(*class) - offset);
> -	WARN_ON_ONCE(!class->lock_entry.next);
> -	WARN_ON_ONCE(!list_empty(&class->locks_after));
> -	WARN_ON_ONCE(!list_empty(&class->locks_before));
>  }
>  
>  static inline int within(const void *addr, void *start, unsigned long size)
> -- 
> 2.27.0
> 

Yeah, except that this doesn't build because it conflicts with a
previous patch you actually Acked:

 https://lore.kernel.org/all/20211213132618.105737-1-xiujianfeng@xxxxxxxxxx/T/#m0e9474a9204ec29fb2135135ce3134640a3f27b5