linux-kernel - Re: [PATCH v2] nvmet: fix mar and mor off-by-one errors

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Message-ID: <d3b4ef13-62fc-1bf4-3a5d-3cc740df82b8@nvidia.com>
Date:   Tue, 6 Sep 2022 21:53:18 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Dennis Maisenbacher <Dennis.Maisenbacher@....com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
CC:     Niklas Cassel <niklas.cassel@....com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <chaitanyak@...dia.com>,
        Damien Le Moal <damien.lemoal@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] nvmet: fix mar and mor off-by-one errors

On 9/6/22 00:39, Dennis Maisenbacher wrote:
> From: Dennis Maisenbacher <dennis.maisenbacher@....com>
> 
> Maximum Active Resources (MAR) and Maximum Open Resources (MOR) are 0's
> based vales where a value of 0xffffffff indicates that there is no limit.
> 
> Decrement the values that are returned by bdev_max_open_zones and
> bdev_max_active_zones as the block layer helpers are not 0's based.
> A 0 returned by the block layer helpers indicates no limit, thus convert
> it to 0xffffffff (U32_MAX).
> 
> Fixes: aaf2e048af27 ("nvmet: add ZBD over ZNS backend support")
> Suggested-by: Niklas Cassel <niklas.cassel@....com>
> Signed-off-by: Dennis Maisenbacher <dennis.maisenbacher@....com>
> ---
> Changes in v2:
>      - Add explicit check if block layer helpers return a 0 and if so
>      convert it to U32_MAX.
>      - Add Fixes tag.
> 
>   drivers/nvme/target/zns.c | 17 +++++++++++++++--
>   1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/target/zns.c b/drivers/nvme/target/zns.c
> index c7ef69f29fe4..eae81f939067 100644
> --- a/drivers/nvme/target/zns.c
> +++ b/drivers/nvme/target/zns.c
> @@ -100,6 +100,7 @@ void nvmet_execute_identify_cns_cs_ns(struct nvmet_req *req)
>   	struct nvme_id_ns_zns *id_zns;
>   	u64 zsze;
>   	u16 status;
> +	u32 mar, mor;

consider :-
  +	u32 mar, mor;
    	u64 zsze;
    	u16 status;

>   
>   	if (le32_to_cpu(req->cmd->identify.nsid) == NVME_NSID_ALL) {
>   		req->error_loc = offsetof(struct nvme_identify, nsid);
> @@ -130,8 +131,20 @@ void nvmet_execute_identify_cns_cs_ns(struct nvmet_req *req)
>   	zsze = (bdev_zone_sectors(req->ns->bdev) << 9) >>
>   					req->ns->blksize_shift;
>   	id_zns->lbafe[0].zsze = cpu_to_le64(zsze);
> -	id_zns->mor = cpu_to_le32(bdev_max_open_zones(req->ns->bdev));
> -	id_zns->mar = cpu_to_le32(bdev_max_active_zones(req->ns->bdev));
> +
> +	mor = bdev_max_open_zones(req->ns->bdev);
> +	if (!mor)
> +		mor = U32_MAX;
> +	else
> +		--mor;
> +	id_zns->mor = cpu_to_le32(mor);
> +
> +	mar = bdev_max_active_zones(req->ns->bdev);
> +	if (!mar)
> +		mar = U32_MAX;
> +	else
> +		--mar;
> +	id_zns->mar = cpu_to_le32(mar);
>   

above 14 lines of code can be simplified as in 4-5 lines :-

mor = bdev_max_open_zones(req->ns->bdev);
id->zns->mor = cpu_tp_le32(mor ? mor - 1 : U32_MAX);

mar = bdev_max_active_zones(req->ns->bdev);
id->zns->mar = cpu_tp_le32(mar ? mar - 1 : U32_MAX);

>   done:
>   	status = nvmet_copy_to_sgl(req, 0, id_zns, sizeof(*id_zns));


either way,

Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>