Re: [PATCH] nvme: fix handling single range discard request

[Sagi Grimberg <sagi@grimberg.me>]

On 3/4/23 01:13, Ming Lei wrote:
> When investigating one customer report on warning in nvme_setup_discard,
> we observed the controller(nvme/tcp) actually exposes
> queue_max_discard_segments(req->q) == 1.
> 
> Obviously the current code can't handle this situation, since contiguity
> merge like normal RW request is taken.
> 
> Fix the issue by building range from request sector/nr_sectors directly.
> 
> Fixes: b35ba01ea697 ("nvme: support ranged discard requests")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>   drivers/nvme/host/core.c | 28 +++++++++++++++++++---------
>   1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index c2730b116dc6..d4be525f8100 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -781,16 +781,26 @@ static blk_status_t nvme_setup_discard(struct nvme_ns *ns, struct request *req,
>   		range = page_address(ns->ctrl->discard_page);
>   	}
>   
> -	__rq_for_each_bio(bio, req) {
> -		u64 slba = nvme_sect_to_lba(ns, bio->bi_iter.bi_sector);
> -		u32 nlb = bio->bi_iter.bi_size >> ns->lba_shift;
> -
> -		if (n < segments) {
> -			range[n].cattr = cpu_to_le32(0);
> -			range[n].nlb = cpu_to_le32(nlb);
> -			range[n].slba = cpu_to_le64(slba);
> +	if (queue_max_discard_segments(req->q) == 1) {
> +		u64 slba = nvme_sect_to_lba(ns, blk_rq_pos(req));
> +		u32 nlb = blk_rq_sectors(req) >> (ns->lba_shift - 9);
> +
> +		range[0].cattr = cpu_to_le32(0);
> +		range[0].nlb = cpu_to_le32(nlb);
> +		range[0].slba = cpu_to_le64(slba);
> +		n = 1;
> +	} else {
> +		__rq_for_each_bio(bio, req) {
> +			u64 slba = nvme_sect_to_lba(ns, bio->bi_iter.bi_sector);
> +			u32 nlb = bio->bi_iter.bi_size >> ns->lba_shift;
> +
> +			if (n < segments) {
> +				range[n].cattr = cpu_to_le32(0);
> +				range[n].nlb = cpu_to_le32(nlb);
> +				range[n].slba = cpu_to_le64(slba);
> +			}
> +			n++;
>   		}
> -		n++;
>   	}
>   
>   	if (WARN_ON_ONCE(n != segments)) {


Maybe just set segments to min(blk_rq_nr_discard_segments(req), 
queue_max_discard_segments(req->q)) and let the existing code do
its thing?