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

[Max Gurtovoy]

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 <log...@deltatee.com>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Sagi Grimberg <s...@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;