Re: [PATCHv5 3/5] block: introduce alloc_sched_data and free_sched_data elevator methods

[Ming Lei <ming.lei@redhat.com>]

On Wed, Nov 12, 2025 at 10:56:04AM +0530, Nilay Shroff wrote:
> The recent lockdep splat [1] highlights a potential deadlock risk
> involving ->elevator_lock and ->freeze_lock dependencies on -pcpu_alloc_
> mutex. The trace shows that the issue occurs when the Kyber scheduler
> allocates dynamic memory for its elevator data during initialization.
> 
> To address this, introduce two new elevator operation callbacks:
> ->alloc_sched_data and ->free_sched_data. The subsequent patch would
> build upon these newly introduced methods to suppress lockdep splat[1].
> 
> [1] https://lore.kernel.org/all/CAGVVp+VNW4M-5DZMNoADp6o2VKFhi7KxWpTDkcnVyjO0=-D5+A@mail.gmail.com/
> 
> Reviewed-by: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
> ---
>  block/blk-mq-sched.h | 15 +++++++++++++++
>  block/elevator.h     |  2 ++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
> index 1f8e58dd4b49..3ac64b66176a 100644
> --- a/block/blk-mq-sched.h
> +++ b/block/blk-mq-sched.h
> @@ -39,6 +39,21 @@ void blk_mq_free_sched_res(struct elevator_resources *res,
>  void blk_mq_free_sched_res_batch(struct xarray *et_table,
>  		struct blk_mq_tag_set *set);
>  
> +static inline void *blk_mq_alloc_sched_data(struct request_queue *q,
> +		struct elevator_type *e)
> +{
> +	if (e && e->ops.alloc_sched_data)
> +		return e->ops.alloc_sched_data(q);
> +
> +	return 0;

s/0/NULL


thanks,
Ming