Re: [PATCH v5 3/6] nvme-tcp: short-circuit reconnect retries

[Sagi Grimberg <sagi@grimberg.me>]

On 09/04/2024 12:35, Daniel Wagner wrote:
> From: Hannes Reinecke <hare@suse.de>
>
> Returning an nvme status from nvme_tcp_setup_ctrl() indicates that the
> association was established and we have received a status from the
> controller; consequently we should honour the DNR bit. If not any future
> reconnect attempts will just return the same error, so we can
> short-circuit the reconnect attempts and fail the connection directly.
>
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> [dwagner: add helper to decide to reconnect]
> Signed-off-by: Daniel Wagner <dwagner@suse.de>
> ---
>   drivers/nvme/host/nvme.h | 24 ++++++++++++++++++++++++
>   drivers/nvme/host/tcp.c  | 23 +++++++++++++++--------
>   2 files changed, 39 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 9b8904a476b8..dfe103283a3d 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -701,6 +701,30 @@ static inline bool nvme_is_path_error(u16 status)
>   	return (status & 0x700) == 0x300;
>   }
>   
> +/*
> + * Evaluate the status information returned by the LLDD

We usually say transport, less so LLDD.

>   in order to
> + * decided if a reconnect attempt should be scheduled.
> + *
> + * There are two cases where no reconnect attempt should be attempted:
> + *
> + * 1) The LLDD reports an negative status. There was an error (e.g. no
> + *    memory) on the host side and thus abort the operation.
> + *    Note, there are exception such as ENOTCONN which is
> + *    not an internal driver error, thus we filter these errors
> + *    out and retry later.

What is this ENOTCONN here? From what I see its just a random
escape value to bypass the status check. I think that 0 would do the same
wouldn't it?

> + * 2) The DNR bit is set and the specification states no further
> + *    connect attempts with the same set of paramenters should be
> + *    attempted.
> + */
> +static inline bool nvme_ctrl_reconnect(int status)
> +{
> +	if (status < 0 && status != -ENOTCONN)
> +		return false;
> +	else if (status > 0 && (status & NVME_SC_DNR))
> +		return false;
> +	return true;
> +}
> +
>   /*
>    * Fill in the status and result information from the CQE, and then figure out
>    * if blk-mq will need to use IPI magic to complete the request, and if yes do
> diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
> index fdbcdcedcee9..7e25a96e9870 100644
> --- a/drivers/nvme/host/tcp.c
> +++ b/drivers/nvme/host/tcp.c
> @@ -2155,9 +2155,11 @@ static void nvme_tcp_teardown_io_queues(struct nvme_ctrl *ctrl,
>   	nvme_tcp_destroy_io_queues(ctrl, remove);
>   }
>   
> -static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl)
> +static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl,
> +		int status)
>   {
>   	enum nvme_ctrl_state state = nvme_ctrl_state(ctrl);
> +	bool recon = nvme_ctrl_reconnect(status);
>   
>   	/* If we are resetting/deleting then do nothing */
>   	if (state != NVME_CTRL_CONNECTING) {
> @@ -2165,13 +2167,14 @@ static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl)
>   		return;
>   	}
>   
> -	if (nvmf_should_reconnect(ctrl)) {
> +	if (recon && nvmf_should_reconnect(ctrl)) {

its weird to have a condition that checks _and_ condition
of two different "should reconnect" conditions.

Why don't we simply pass the status to nvmf_should_reconnect()
and evaluate there?

>   		dev_info(ctrl->device, "Reconnecting in %d seconds...\n",
>   			ctrl->opts->reconnect_delay);
>   		queue_delayed_work(nvme_wq, &to_tcp_ctrl(ctrl)->connect_work,
>   				ctrl->opts->reconnect_delay * HZ);
>   	} else {
> -		dev_info(ctrl->device, "Removing controller...\n");
> +		dev_info(ctrl->device, "Removing controller (%d)...\n",
> +			 status);
>   		nvme_delete_ctrl(ctrl);
>   	}
>   }
> @@ -2252,10 +2255,12 @@ static void nvme_tcp_reconnect_ctrl_work(struct work_struct *work)
>   	struct nvme_tcp_ctrl *tcp_ctrl = container_of(to_delayed_work(work),
>   			struct nvme_tcp_ctrl, connect_work);
>   	struct nvme_ctrl *ctrl = &tcp_ctrl->ctrl;
> +	int ret;
>   
>   	++ctrl->nr_reconnects;
>   
> -	if (nvme_tcp_setup_ctrl(ctrl, false))
> +	ret = nvme_tcp_setup_ctrl(ctrl, false);
> +	if (ret)
>   		goto requeue;
>   
>   	dev_info(ctrl->device, "Successfully reconnected (%d attempt)\n",
> @@ -2268,7 +2273,7 @@ static void nvme_tcp_reconnect_ctrl_work(struct work_struct *work)
>   requeue:
>   	dev_info(ctrl->device, "Failed reconnect attempt %d\n",
>   			ctrl->nr_reconnects);
> -	nvme_tcp_reconnect_or_remove(ctrl);
> +	nvme_tcp_reconnect_or_remove(ctrl, ret);
>   }
>   
>   static void nvme_tcp_error_recovery_work(struct work_struct *work)
> @@ -2295,7 +2300,7 @@ static void nvme_tcp_error_recovery_work(struct work_struct *work)
>   		return;
>   	}
>   
> -	nvme_tcp_reconnect_or_remove(ctrl);
> +	nvme_tcp_reconnect_or_remove(ctrl, -ENOTCONN);
>   }
>   
>   static void nvme_tcp_teardown_ctrl(struct nvme_ctrl *ctrl, bool shutdown)
> @@ -2315,6 +2320,7 @@ static void nvme_reset_ctrl_work(struct work_struct *work)
>   {
>   	struct nvme_ctrl *ctrl =
>   		container_of(work, struct nvme_ctrl, reset_work);
> +	int ret;
>   
>   	nvme_stop_ctrl(ctrl);
>   	nvme_tcp_teardown_ctrl(ctrl, false);
> @@ -2328,14 +2334,15 @@ static void nvme_reset_ctrl_work(struct work_struct *work)
>   		return;
>   	}
>   
> -	if (nvme_tcp_setup_ctrl(ctrl, false))
> +	ret = nvme_tcp_setup_ctrl(ctrl, false);
> +	if (ret)
>   		goto out_fail;
>   
>   	return;
>   
>   out_fail:
>   	++ctrl->nr_reconnects;
> -	nvme_tcp_reconnect_or_remove(ctrl);
> +	nvme_tcp_reconnect_or_remove(ctrl, ret);
>   }
>   
>   static void nvme_tcp_stop_ctrl(struct nvme_ctrl *ctrl)