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Date: Fri, 17 Aug 2018 17:33:51 +0800
From: Ming Lei <tom.leiming@...il.com>
To: Jianchao Wang <jianchao.w.wang@...cle.com>
Cc: Jens Axboe <axboe@...nel.dk>,
Bart Van Assche <bart.vanassche@....com>,
Keith Busch <keith.busch@...ux.intel.com>,
linux-block <linux-block@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/2] blk-mq: init hctx sched after update ctx and hctx mapping
On Fri, Aug 17, 2018 at 11:54 AM, Jianchao Wang
<jianchao.w.wang@...cle.com> wrote:
> Currently, when update nr_hw_queues, io scheduler's init_hctx will
> be invoked before the mapping between ctx and hctx is adapted
> correctly by blk_mq_map_swqueue. The io scheduler init_hctx (kyber)
> may depend on this mapping and get wrong result and panic finally.
> A simply way to fix this is switch the io scheduler to none before
> update the nr_hw_queues, and then get it back after update nr_hw_queues.
> To achieve this, we add a new member elv_type in request_queue to
> save the original elevator and adapt and export elevator_switch_mq.
> And also blk_mq_sched_init_/exit_hctx are removed due to nobody use
> them any more.
>
> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
> ---
> block/blk-mq-sched.c | 44 --------------------------------------------
> block/blk-mq-sched.h | 5 -----
> block/blk-mq.c | 36 ++++++++++++++++++++++++++++--------
> block/blk.h | 2 ++
> block/elevator.c | 20 ++++++++++++--------
> include/linux/blkdev.h | 3 +++
> 6 files changed, 45 insertions(+), 65 deletions(-)
>
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index cf9c66c..29bfe80 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -462,50 +462,6 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q)
> blk_mq_sched_free_tags(set, hctx, i);
> }
>
> -int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
> - unsigned int hctx_idx)
> -{
> - struct elevator_queue *e = q->elevator;
> - int ret;
> -
> - if (!e)
> - return 0;
> -
> - ret = blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
> - if (ret)
> - return ret;
> -
> - if (e->type->ops.mq.init_hctx) {
> - ret = e->type->ops.mq.init_hctx(hctx, hctx_idx);
> - if (ret) {
> - blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
> - return ret;
> - }
> - }
> -
> - blk_mq_debugfs_register_sched_hctx(q, hctx);
> -
> - return 0;
> -}
> -
> -void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
> - unsigned int hctx_idx)
> -{
> - struct elevator_queue *e = q->elevator;
> -
> - if (!e)
> - return;
> -
> - blk_mq_debugfs_unregister_sched_hctx(hctx);
> -
> - if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
> - e->type->ops.mq.exit_hctx(hctx, hctx_idx);
> - hctx->sched_data = NULL;
> - }
> -
> - blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
> -}
> -
> int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
> {
> struct blk_mq_hw_ctx *hctx;
> diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
> index 0cb8f93..4e028ee 100644
> --- a/block/blk-mq-sched.h
> +++ b/block/blk-mq-sched.h
> @@ -28,11 +28,6 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx);
> int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e);
> void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);
>
> -int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
> - unsigned int hctx_idx);
> -void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
> - unsigned int hctx_idx);
> -
> static inline bool
> blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
> {
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 5efd789..de7027f 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2147,8 +2147,6 @@ static void blk_mq_exit_hctx(struct request_queue *q,
> if (set->ops->exit_request)
> set->ops->exit_request(set, hctx->fq->flush_rq, hctx_idx);
>
> - blk_mq_sched_exit_hctx(q, hctx, hctx_idx);
> -
> if (set->ops->exit_hctx)
> set->ops->exit_hctx(hctx, hctx_idx);
>
> @@ -2216,12 +2214,9 @@ static int blk_mq_init_hctx(struct request_queue *q,
> set->ops->init_hctx(hctx, set->driver_data, hctx_idx))
> goto free_bitmap;
>
> - if (blk_mq_sched_init_hctx(q, hctx, hctx_idx))
> - goto exit_hctx;
> -
> hctx->fq = blk_alloc_flush_queue(q, hctx->numa_node, set->cmd_size);
> if (!hctx->fq)
> - goto sched_exit_hctx;
> + goto exit_hctx;
>
> if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx, node))
> goto free_fq;
> @@ -2235,8 +2230,6 @@ static int blk_mq_init_hctx(struct request_queue *q,
>
> free_fq:
> kfree(hctx->fq);
> - sched_exit_hctx:
> - blk_mq_sched_exit_hctx(q, hctx, hctx_idx);
> exit_hctx:
> if (set->ops->exit_hctx)
> set->ops->exit_hctx(hctx, hctx_idx);
> @@ -2913,6 +2906,25 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
> list_for_each_entry(q, &set->tag_list, tag_set_list)
> blk_mq_freeze_queue(q);
>
> + /*
> + * switch io scheduler to NULL to clean up the data in it.
> + * will get it back after update mapping between cpu and hw queues.
> + */
> + list_for_each_entry(q, &set->tag_list, tag_set_list) {
> + if (!q->elevator) {
> + q->elv_type = NULL;
> + continue;
> + }
> + q->elv_type = q->elevator->type;
> + mutex_lock(&q->sysfs_lock);
> + /*
> + * elevator_release will put it.
> + */
> + __module_get(q->elv_type->elevator_owner);
I understand what elevator_release() frees is the 'ref-counter' got in
elevator_get(), but who will be the counter-pair of the above __module_get()?
Thanks,
Ming Lei
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