Re: [PATCH 1/5] blk-mq: Move flush queue allocation into blk_mq_init_hctx()

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

在 2025/08/01 19:44, Ming Lei 写道:
> Move flush queue allocation into blk_mq_init_hctx() and its release into
> blk_mq_exit_hctx(), and prepare for replacing tags->lock with SRCU to
> draining inflight request walking. blk_mq_exit_hctx() is the last chance
> for us to get valid `tag_set` reference, and we need to add one SRCU to
> `tag_set` for freeing flush request via call_srcu().
>
> It is safe to move flush queue & request release into blk_mq_exit_hctx(),
> because blk_mq_clear_flush_rq_mapping() clears the flush request
> reference int driver tags inflight request table, meantime inflight
> request walking is drained.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
>   block/blk-mq-sysfs.c |  1 -
>   block/blk-mq.c       | 20 +++++++++++++-------
>   2 files changed, 13 insertions(+), 8 deletions(-)
LGTM
Reviewed-by: Yu Kuai <yukuai3@xxxxxxxxxx>

> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index 24656980f443..c8dfed6c1c96 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -34,7 +34,6 @@ static void blk_mq_hw_sysfs_release(struct kobject *kobj)
>   	struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx,
>   						  kobj);
>   
> -	blk_free_flush_queue(hctx->fq);
>   	sbitmap_free(&hctx->ctx_map);
>   	free_cpumask_var(hctx->cpumask);
>   	kfree(hctx->ctxs);
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 9692fa4c3ef2..c6a1366dbe77 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3939,6 +3939,9 @@ static void blk_mq_exit_hctx(struct request_queue *q,
>   	if (set->ops->exit_hctx)
>   		set->ops->exit_hctx(hctx, hctx_idx);
>   
> +	blk_free_flush_queue(hctx->fq);
> +	hctx->fq = NULL;
> +
>   	xa_erase(&q->hctx_table, hctx_idx);
>   
>   	spin_lock(&q->unused_hctx_lock);
> @@ -3964,13 +3967,19 @@ static int blk_mq_init_hctx(struct request_queue *q,
>   		struct blk_mq_tag_set *set,
>   		struct blk_mq_hw_ctx *hctx, unsigned hctx_idx)
>   {
> +	gfp_t gfp = GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY;
> +
> +	hctx->fq = blk_alloc_flush_queue(hctx->numa_node, set->cmd_size, gfp);
> +	if (!hctx->fq)
> +		goto fail;
> +
>   	hctx->queue_num = hctx_idx;
>   
>   	hctx->tags = set->tags[hctx_idx];
>   
>   	if (set->ops->init_hctx &&
>   	    set->ops->init_hctx(hctx, set->driver_data, hctx_idx))
> -		goto fail;
> +		goto fail_free_fq;
>   
>   	if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx,
>   				hctx->numa_node))
> @@ -3987,6 +3996,9 @@ static int blk_mq_init_hctx(struct request_queue *q,
>    exit_hctx:
>   	if (set->ops->exit_hctx)
>   		set->ops->exit_hctx(hctx, hctx_idx);
> + fail_free_fq:
> +	blk_free_flush_queue(hctx->fq);
> +	hctx->fq = NULL;
>    fail:
>   	return -1;
>   }
> @@ -4038,16 +4050,10 @@ blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set,
>   	init_waitqueue_func_entry(&hctx->dispatch_wait, blk_mq_dispatch_wake);
>   	INIT_LIST_HEAD(&hctx->dispatch_wait.entry);
>   
> -	hctx->fq = blk_alloc_flush_queue(hctx->numa_node, set->cmd_size, gfp);
> -	if (!hctx->fq)
> -		goto free_bitmap;
> -
>   	blk_mq_hctx_kobj_init(hctx);
>   
>   	return hctx;
>   
> - free_bitmap:
> -	sbitmap_free(&hctx->ctx_map);
>    free_ctxs:
>   	kfree(hctx->ctxs);
>    free_cpumask: