[PATCH v4 2/3] nvme: allow local retry and proper failover for REQ_FAILFAST_TRANSPORT

[Mike Snitzer]

REQ_FAILFAST_TRANSPORT is set by upper layer software that handles
multipathing. Unlike SCSI, NVMe's error handling was specifically
designed to handle local retry for non-path errors. As such, allow
NVMe's local retry mechanism to be used for requests marked with
REQ_FAILFAST_TRANSPORT.

In this way, the mechanism of NVMe multipath or other multipath are
now equivalent. The mechanism is: non path related error will be
retried locally, path related error is handled by multipath.

Also, introduce FAILUP handling for REQ_FAILFAST_TRANSPORT. 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.

nvme_complete_rq() is updated to call nvme_failup_req() if
nvme_decide_disposition() returns FAILUP. nvme_failup_req() ensures
the request is completed with a retryable path error.

Signed-off-by: Mike Snitzer <snitzer at redhat.com>
---
 drivers/nvme/host/core.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 540d6fd8ffef..a12b10a1383c 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)
@@ -306,15 +307,16 @@ 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) ||
+	if ((req->cmd_flags & (REQ_FAILFAST_DEV | REQ_FAILFAST_DRIVER)) ||
 	    (nvme_req(req)->status & NVME_SC_DNR) ||
 	    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;
@@ -336,6 +338,12 @@ static inline void nvme_end_req(struct request *req)
 	blk_mq_end_request(req, status);
 }
 
+static inline void nvme_failup_req(struct request *req)
+{
+	nvme_req(req)->status = NVME_SC_HOST_PATH_ERROR;
+	nvme_end_req(req);
+}
+
 void nvme_complete_rq(struct request *req)
 {
 	trace_nvme_complete_rq(req);
@@ -354,6 +362,9 @@ 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);
-- 
2.15.0