[PATCH V2 11/13] block: move blk_exit_queue into disk_release

[Christoph Hellwig]

On Sat, Jan 22, 2022 at 07:10:52PM +0800, Ming Lei wrote:
>  3 files changed, 41 insertions(+), 17 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index d51b0aa2e4e4..72ae9955cf27 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3101,6 +3101,9 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
>  	struct blk_mq_tags *drv_tags;
>  	struct page *page;
>  
> +	if (list_empty(&tags->page_list))
> +		return;

Please split this out and document why it is needed.

> +/* Unconfigure the I/O scheduler and dissociate from the cgroup controller. */
> +static void blk_exit_queue(struct request_queue *q)
> +{
> +	/*
> +	 * Since the I/O scheduler exit code may access cgroup information,
> +	 * perform I/O scheduler exit before disassociating from the block
> +	 * cgroup controller.
> +	 */
> +	if (q->elevator) {
> +		ioc_clear_queue(q);
> +
> +		mutex_lock(&q->sysfs_lock);
> +		blk_mq_sched_free_rqs(q);
> +		elevator_exit(q);
> +		mutex_unlock(&q->sysfs_lock);
> +	}
> +}

Given that this all deals with the I/O scheduler the naming seems
wrong.  It almost seems like we'd want to move ioc_clear_queue and
blk_mq_sched_free_rqs into elevator_exit to have somewhat sensible
helpers.  That would add extra locking of q->sysfs_lock for
ioc_clear_queue, but given that elevator_switch_mq already does
that, this seems harmless.