[dm-devel] [PATCH v2 3/4] nvme: introduce FAILUP handling for REQ_FAILFAST_TRANSPORT

[Hannes Reinecke]

On 4/16/21 1:15 AM, Mike Snitzer wrote:
> If REQ_FAILFAST_TRANSPORT is set it means the driver should not retry
> IO that completed with transport errors. REQ_FAILFAST_TRANSPORT is
> set by multipathing software (e.g. dm-multipath) before it issues IO.
> 
> Update NVMe to allow failover of requests marked with either
> REQ_NVME_MPATH or REQ_FAILFAST_TRANSPORT. This allows such requests
> to be given a disposition of either FAILOVER or FAILUP respectively.
> FAILUP handling ensures a retryable error is returned up from NVMe.
> 
> Introduce nvme_failup_req() for use in nvme_complete_rq() if
> nvme_decide_disposition() returns FAILUP. nvme_failup_req() ensures
> the request is completed with a retryable IO error when appropriate.
> __nvme_end_req() was factored out for use by both nvme_end_req() and
> nvme_failup_req().
> 
> Signed-off-by: Mike Snitzer <snitzer at redhat.com>
> ---
>  drivers/nvme/host/core.c | 31 ++++++++++++++++++++++++++-----
>  1 file changed, 26 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 4134cf3c7e48..10375197dd53 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -299,6 +299,7 @@ enum nvme_disposition {
>  	COMPLETE,
>  	RETRY,
>  	FAILOVER,
> +	FAILUP,
>  };
>  
>  static inline enum nvme_disposition nvme_decide_disposition(struct request *req)
> @@ -318,10 +319,11 @@ static inline enum nvme_disposition nvme_decide_disposition(struct request *req)
>  	    nvme_req(req)->retries >= nvme_max_retries)
>  		return COMPLETE;
>  
> -	if (req->cmd_flags & REQ_NVME_MPATH) {
> +	if (req->cmd_flags & (REQ_NVME_MPATH | REQ_FAILFAST_TRANSPORT)) {
>  		if (nvme_is_path_error(nvme_req(req)->status) ||
>  		    blk_queue_dying(req->q))
> -			return FAILOVER;
> +			return (req->cmd_flags & REQ_NVME_MPATH) ?
> +				FAILOVER : FAILUP;
>  	} else {
>  		if (blk_queue_dying(req->q))
>  			return COMPLETE;
> @@ -330,10 +332,8 @@ static inline enum nvme_disposition nvme_decide_disposition(struct request *req)
>  	return RETRY;
>  }
>  
> -static inline void nvme_end_req(struct request *req)
> +static inline void __nvme_end_req(struct request *req, blk_status_t status)
>  {
> -	blk_status_t status = nvme_error_status(nvme_req(req)->status);
> -
>  	if (IS_ENABLED(CONFIG_BLK_DEV_ZONED) &&
>  	    req_op(req) == REQ_OP_ZONE_APPEND)
>  		req->__sector = nvme_lba_to_sect(req->q->queuedata,
> @@ -343,6 +343,24 @@ static inline void nvme_end_req(struct request *req)
>  	blk_mq_end_request(req, status);
>  }
>  
> +static inline void nvme_end_req(struct request *req)
> +{
> +	__nvme_end_req(req, nvme_error_status(nvme_req(req)->status));
> +}
> +
> +static void nvme_failup_req(struct request *req)
> +{
> +	blk_status_t status = nvme_error_status(nvme_req(req)->status);
> +
> +	if (WARN_ON_ONCE(!blk_path_error(status))) {
> +		pr_debug("Request meant for failover but blk_status_t (errno=%d) was not retryable.\n",
> +			 blk_status_to_errno(status));
> +		status = BLK_STS_IOERR;
> +	}
> +
> +	__nvme_end_req(req, status);
> +}
> +
>  void nvme_complete_rq(struct request *req)
>  {
>  	trace_nvme_complete_rq(req);
> @@ -361,6 +379,9 @@ void nvme_complete_rq(struct request *req)
>  	case FAILOVER:
>  		nvme_failover_req(req);
>  		return;
> +	case FAILUP:
> +		nvme_failup_req(req);
> +		return;
>  	}
>  }
>  EXPORT_SYMBOL_GPL(nvme_complete_rq);
> 

Hmm. Quite convoluted, methinks.
Shouldn't this achieve the same thing?

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index e89ec2522ca6..8c36a2196b66 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -303,8 +303,10 @@ static inline enum nvme_disposition
nvme_decide_disposition(struct request *req)
        if (likely(nvme_req(req)->status == 0))
                return COMPLETE;

-       if (blk_noretry_request(req) ||
-           (nvme_req(req)->status & NVME_SC_DNR) ||
+       if (blk_noretry_request(req))
+               nvme_req(req)->status |= NVME_SC_DNR;
+
+       if ((nvme_req(req)->status & NVME_SC_DNR) ||
            nvme_req(req)->retries >= nvme_max_retries)
                return COMPLETE;


Cheers,

Hannes
-- 
Dr. Hannes Reinecke		        Kernel Storage Architect
hare at suse.de			               +49 911 74053 688
SUSE Software Solutions Germany GmbH, 90409 Nürnberg
GF: F. Imendörffer, HRB 36809 (AG Nürnberg)