Re: [PATCHv4 4/5] block: use {alloc|free}_sched data methods

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

On Mon, Nov 10, 2025 at 01:44:51PM +0530, Nilay Shroff wrote:
> The previous patch introduced ->alloc_sched_data and
> ->free_sched_data methods. This patch builds upon that
> by now using these methods during elevator switch and
> nr_hw_queue update.
> 
> It's also ensured that scheduler-specific data is
> allocated and freed through the new callbacks outside
> of the ->freeze_lock and ->elevator_lock locking contexts,
> thereby preventing any dependency on pcpu_alloc_mutex.
> 
> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
> ---
>  block/blk-mq-sched.c | 32 ++++++++++++++++++++++++--------
>  block/blk-mq-sched.h |  8 ++++++--
>  block/elevator.c     | 34 ++++++++++++++++++++++------------
>  block/elevator.h     |  4 +++-
>  4 files changed, 55 insertions(+), 23 deletions(-)
> 
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index c7091ea4dccd..0ea8f0004274 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -428,12 +428,17 @@ void blk_mq_free_sched_tags(struct elevator_tags *et,
>  }
>  
>  void blk_mq_free_sched_res(struct elevator_resources *res,
> +		struct elevator_type *type,
>  		struct blk_mq_tag_set *set)
>  {
>  	if (res->et) {
>  		blk_mq_free_sched_tags(res->et, set);
>  		res->et = NULL;
>  	}
> +	if (res->data) {
> +		blk_mq_free_sched_data(type, res->data);
> +		res->data = NULL;
> +	}
>  }
>  
>  void blk_mq_free_sched_res_batch(struct xarray *elv_tbl,
> @@ -458,7 +463,7 @@ void blk_mq_free_sched_res_batch(struct xarray *elv_tbl,
>  				WARN_ON_ONCE(1);
>  				continue;
>  			}
> -			blk_mq_free_sched_res(&ctx->res, set);
> +			blk_mq_free_sched_res(&ctx->res, ctx->type, set);
>  		}
>  	}
>  }
> @@ -540,15 +545,24 @@ struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
>  	return NULL;
>  }
>  
> -int blk_mq_alloc_sched_res(struct elevator_resources *res,
> -		struct blk_mq_tag_set *set, unsigned int nr_hw_queues)
> +int blk_mq_alloc_sched_res(struct request_queue *q,
> +		struct elevator_type *type,
> +		struct elevator_resources *res,
> +		struct blk_mq_tag_set *set,
> +		unsigned int nr_hw_queues)

As mentioned, `struct request_queue *q` parameter can be added from
beginning, then `struct blk_mq_tag_set *set` can be avoided.

Otherwise, this patch looks fine.

Thanks,
Ming