Re: [RFC PATCH 4/5] scsi: ufs: L2P map management for HPB read

[Bart Van Assche <bvanassche@acm.org>]

On 2020-06-04 18:56, Daejun Park wrote:
> +static struct ufshpb_req *ufshpb_get_map_req(struct ufshpb_lu *hpb,
> +					     struct ufshpb_subregion *srgn)
> +{
> +	struct ufshpb_req *map_req;
> +	struct request *req;
> +	struct bio *bio;
> +
> +	map_req = kmem_cache_alloc(hpb->map_req_cache, GFP_KERNEL);
> +	if (!map_req)
> +		return NULL;
> +
> +	req = blk_get_request(hpb->sdev_ufs_lu->request_queue,
> +			      REQ_OP_SCSI_IN, BLK_MQ_REQ_PREEMPT);
> +	if (IS_ERR(req))
> +		goto free_map_req;
> +
> +	bio = bio_alloc(GFP_KERNEL, hpb->pages_per_srgn);
> +	if (!bio) {
> +		blk_put_request(req);
> +		goto free_map_req;
> +	}
> +
> +	map_req->hpb = hpb;
> +	map_req->req = req;
> +	map_req->bio = bio;
> +
> +	map_req->rgn_idx = srgn->rgn_idx;
> +	map_req->srgn_idx = srgn->srgn_idx;
> +	map_req->mctx = srgn->mctx;
> +	map_req->lun = hpb->lun;
> +
> +	return map_req;
> +free_map_req:
> +	kmem_cache_free(hpb->map_req_cache, map_req);
> +	return NULL;
> +}

Will blk_get_request() fail if all tags have been allocated? Can that
cause a deadlock or infinite loop?

> +static inline void ufshpb_set_read_buf_cmd(unsigned char *cdb, int rgn_idx,
> +					   int srgn_idx, int srgn_mem_size)
> +{
> +	cdb[0] = UFSHPB_READ_BUFFER;
> +	cdb[1] = UFSHPB_READ_BUFFER_ID;
> +
> +	put_unaligned_be32(srgn_mem_size, &cdb[5]);
> +	/* cdb[5] = 0x00; */
> +	put_unaligned_be16(rgn_idx, &cdb[2]);
> +	put_unaligned_be16(srgn_idx, &cdb[4]);
> +
> +	cdb[9] = 0x00;
> +}

So the put_unaligned_be32(srgn_mem_size, &cdb[5]) comes first because
the put_unaligned_be16(srgn_idx, &cdb[4]) overwrites byte cdb[5]? That
is really ugly. Please use put_unaligned_be24() instead if that is what
you meant and keep the put_*() calls in increasing cdb offset order.

> +static int ufshpb_map_req_add_bio_page(struct ufshpb_lu *hpb,
> +				       struct request_queue *q, struct bio *bio,
> +				       struct ufshpb_map_ctx *mctx)
> +{
> +	int i, ret = 0;
> +
> +	for (i = 0; i < hpb->pages_per_srgn; i++) {
> +		ret = bio_add_pc_page(q, bio, mctx->m_page[i], PAGE_SIZE, 0);
> +		if (ret != PAGE_SIZE) {
> +			dev_notice(&hpb->hpb_lu_dev,
> +				   "bio_add_pc_page fail %d\n", ret);
> +			return -ENOMEM;
> +		}
> +	}
> +
> +	return 0;
> +}

Why bio_add_pc_page() instead of bio_add_page()?

> +static int ufshpb_execute_map_req(struct ufshpb_lu *hpb,
> +				  struct ufshpb_req *map_req)
> +{
> +	struct request_queue *q;
> +	struct request *req;
> +	struct scsi_request *rq;
> +	int ret = 0;
> +
> +	q = hpb->sdev_ufs_lu->request_queue;
> +	ret = ufshpb_map_req_add_bio_page(hpb, q, map_req->bio,
> +					  map_req->mctx);
> +	if (ret) {
> +		dev_notice(&hpb->hpb_lu_dev,
> +			   "map_req_add_bio_page fail %d - %d\n",
> +			   map_req->rgn_idx, map_req->srgn_idx);
> +		return ret;
> +	}
> +
> +	req = map_req->req;
> +
> +	blk_rq_append_bio(req, &map_req->bio);
> +	req->rq_flags |= RQF_QUIET;
> +	req->timeout = MAP_REQ_TIMEOUT;
> +	req->end_io_data = (void *)map_req;
> +
> +	rq = scsi_req(req);
> +	ufshpb_set_read_buf_cmd(rq->cmd, map_req->rgn_idx,
> +				map_req->srgn_idx, hpb->srgn_mem_size);
> +	rq->cmd_len = HPB_READ_BUFFER_CMD_LENGTH;
> +
> +	blk_execute_rq_nowait(q, NULL, req, 1, ufshpb_map_req_compl_fn);
> +
> +	atomic_inc(&hpb->stats.map_req_cnt);
> +	return 0;
> +}

Why RQF_QUIET?

Why a custom timeout instead of the SCSI LUN timeout?

Can this function be made asynchronous such that it does not have to be
executed on the context of a workqueue?

Thanks,

Bart.