[PATCH v3 1/4] nvmet: support fabrics sq flow control

[sagi@grimberg.me (Sagi Grimberg)]

> We drop the sq ref in nvmet_req_complete, so this introduces a
> use-after-free.  What about this variant instead:

That is definitely better. I'll give it a test drive.

> 
> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> index e3e158ff207a..74e253eb873f 100644
> --- a/drivers/nvme/target/core.c
> +++ b/drivers/nvme/target/core.c
> @@ -597,25 +597,29 @@ struct nvmet_ns *nvmet_ns_alloc(struct nvmet_subsys *subsys, u32 nsid)
>   	return ns;
>   }
>   
> -static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
> +static void nvmet_update_sq_head(struct nvmet_req *req)
>   {
> -	u32 old_sqhd, new_sqhd;
> -	u16 sqhd;
> -
> -	if (status)
> -		nvmet_set_status(req, status);
> -
>   	if (req->sq->size) {
> +		u32 old_sqhd, new_sqhd;
> +
>   		do {
>   			old_sqhd = req->sq->sqhd;
>   			new_sqhd = (old_sqhd + 1) % req->sq->size;
>   		} while (cmpxchg(&req->sq->sqhd, old_sqhd, new_sqhd) !=
>   					old_sqhd);
>   	}
> -	sqhd = req->sq->sqhd & 0x0000FFFF;
> -	req->rsp->sq_head = cpu_to_le16(sqhd);
> +
> +	req->rsp->sq_head = cpu_to_le16(req->sq->sqhd & 0x0000FFFF);
> +}
> +
> +static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
> +{
> +	if (!req->sq->sqhd_disabled)
> +		nvmet_update_sq_head(req);
>   	req->rsp->sq_id = cpu_to_le16(req->sq->qid);
>   	req->rsp->command_id = req->cmd->common.command_id;
> +	if (status)
> +		nvmet_set_status(req, status);
>   
>   	if (req->ns)
>   		nvmet_put_namespace(req->ns);
> @@ -765,6 +769,7 @@ bool nvmet_req_init(struct nvmet_req *req, struct nvmet_cq *cq,
>   	req->sg_cnt = 0;
>   	req->transfer_len = 0;
>   	req->rsp->status = 0;
> +	req->rsp->sq_head = 0;
>   	req->ns = NULL;
>   
>   	/* no support for fused commands yet */
> diff --git a/drivers/nvme/target/fabrics-cmd.c b/drivers/nvme/target/fabrics-cmd.c
> index d84ae004cb85..328ae46d8344 100644
> --- a/drivers/nvme/target/fabrics-cmd.c
> +++ b/drivers/nvme/target/fabrics-cmd.c
> @@ -115,6 +115,12 @@ static u16 nvmet_install_queue(struct nvmet_ctrl *ctrl, struct nvmet_req *req)
>   	/* note: convert queue size from 0's-based value to 1's-based value */
>   	nvmet_cq_setup(ctrl, req->cq, qid, sqsize + 1);
>   	nvmet_sq_setup(ctrl, req->sq, qid, sqsize + 1);
> +
> +	if (c->cattr & NVME_CONNECT_DISABLE_SQFLOW) {
> +		req->sq->sqhd_disabled = true;
> +		req->rsp->sq_head = cpu_to_le16(0xffff);
> +	}
> +
>   	return 0;
>   }
>   
> diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
> index 31474940e373..ab8e68966e73 100644
> --- a/drivers/nvme/target/nvmet.h
> +++ b/drivers/nvme/target/nvmet.h
> @@ -106,6 +106,7 @@ struct nvmet_sq {
>   	u16			qid;
>   	u16			size;
>   	u32			sqhd;
> +	bool			sqhd_disabled;
>   	struct completion	free_done;
>   	struct completion	confirm_done;
>   };
> diff --git a/include/linux/nvme.h b/include/linux/nvme.h
> index 77d320d32ee5..e7d731776f62 100644
> --- a/include/linux/nvme.h
> +++ b/include/linux/nvme.h
> @@ -1044,6 +1044,10 @@ struct nvmf_disc_rsp_page_hdr {
>   	struct nvmf_disc_rsp_page_entry entries[0];
>   };
>   
> +enum {
> +	NVME_CONNECT_DISABLE_SQFLOW	= (1 << 2),
> +};
> +
>   struct nvmf_connect_command {
>   	__u8		opcode;
>   	__u8		resv1;
>