Re: [PATCH] nvmet: convert from kmap to nvmet_copy_from_sgl

[Max Gurtovoy <maxg@mellanox.com>]

Hi Logan,

On 4/19/2017 2:32 AM, Logan Gunthorpe wrote:
> This is safer as it doesn't rely on the data being stored in
> a single page in an sgl.
>
> It also aids our effort to start phasing out users of sg_page. See [1].
>
> For this we kmalloc some memory, copy to it and free at the end. Note:
> we can't allocate this memory on the stack as the kbuild test robot
> reports some frame size overflows on i386.
>
> [1] https://lwn.net/Articles/720053/
>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Sagi Grimberg <sagi@grimberg.me>
> ---
>  drivers/nvme/target/fabrics-cmd.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/nvme/target/fabrics-cmd.c b/drivers/nvme/target/fabrics-cmd.c
> index 8bd022af..2e0ab10 100644
> --- a/drivers/nvme/target/fabrics-cmd.c
> +++ b/drivers/nvme/target/fabrics-cmd.c
> @@ -122,7 +122,15 @@ static void nvmet_execute_admin_connect(struct nvmet_req *req)
>  	struct nvmet_ctrl *ctrl = NULL;
>  	u16 status = 0;
>
> -	d = kmap(sg_page(req->sg)) + req->sg->offset;
> +	d = kmalloc(sizeof(*d), GFP_KERNEL);

I'd prefer removing the dynamic allocation and use d on the stack to 
simplify the code.
Any thoughts ?

> +	if (!d) {
> +		status = NVME_SC_INTERNAL;
> +		goto complete;
> +	}
> +
> +	status = nvmet_copy_from_sgl(req, 0, d, sizeof(*d));
> +	if (status)
> +		goto out;
>
>  	/* zero out initial completion result, assign values as needed */
>  	req->rsp->result.u32 = 0;
> @@ -143,7 +151,7 @@ static void nvmet_execute_admin_connect(struct nvmet_req *req)
>  	}
>
>  	status = nvmet_alloc_ctrl(d->subsysnqn, d->hostnqn, req,
> -			le32_to_cpu(c->kato), &ctrl);
> +				  le32_to_cpu(c->kato), &ctrl);
>  	if (status)
>  		goto out;
>
> @@ -158,7 +166,8 @@ static void nvmet_execute_admin_connect(struct nvmet_req *req)
>  	req->rsp->result.u16 = cpu_to_le16(ctrl->cntlid);
>
>  out:
> -	kunmap(sg_page(req->sg));
> +	kfree(d);
> +complete:
>  	nvmet_req_complete(req, status);
>  }
>
> @@ -170,7 +179,15 @@ static void nvmet_execute_io_connect(struct nvmet_req *req)
>  	u16 qid = le16_to_cpu(c->qid);
>  	u16 status = 0;
>
> -	d = kmap(sg_page(req->sg)) + req->sg->offset;
> +	d = kmalloc(sizeof(*d), GFP_KERNEL);

here too.

> +	if (!d) {
> +		status = NVME_SC_INTERNAL;
> +		goto complete;
> +	}
> +
> +	status = nvmet_copy_from_sgl(req, 0, d, sizeof(*d));
> +	if (status)
> +		goto out;
>
>  	/* zero out initial completion result, assign values as needed */
>  	req->rsp->result.u32 = 0;
> @@ -183,8 +200,8 @@ static void nvmet_execute_io_connect(struct nvmet_req *req)
>  	}
>
>  	status = nvmet_ctrl_find_get(d->subsysnqn, d->hostnqn,
> -			le16_to_cpu(d->cntlid),
> -			req, &ctrl);
> +				     le16_to_cpu(d->cntlid),
> +				     req, &ctrl);
>  	if (status)
>  		goto out;
>
> @@ -205,7 +222,8 @@ static void nvmet_execute_io_connect(struct nvmet_req *req)
>  	pr_info("adding queue %d to ctrl %d.\n", qid, ctrl->cntlid);
>
>  out:
> -	kunmap(sg_page(req->sg));
> +	kfree(d);
> +complete:
>  	nvmet_req_complete(req, status);
>  	return;
>
>