Re: [PATCH v5 0/3] avoid double request completion and IO error

[Christoph Hellwig <hch@lst.de>]

So I think this is conceptually fine, but I still find the API a little
arcane.  What do you think about the following incremental patch?
If that looks good and tests good for you I can apply the series with
the modifications:

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 0befaad788a094..02579f4f776c7d 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -355,6 +355,21 @@ void nvme_complete_rq(struct request *req)
 }
 EXPORT_SYMBOL_GPL(nvme_complete_rq);
 
+/*
+ * Called to unwind from ->queue_rq on a failed command submission so that the
+ * multipathing code gets called to potentially failover to another path.
+ * The caller needs to unwind all transport specific resource allocations and
+ * must return propagate the return value.
+ */
+blk_status_t nvme_host_path_error(struct request *req)
+{
+	nvme_req(req)->status = NVME_SC_HOST_PATH_ERROR;
+	blk_mq_set_request_complete(req);
+	nvme_complete_rq(req);
+	return BLK_STS_OK;
+}
+EXPORT_SYMBOL_GPL(nvme_host_path_error);
+
 bool nvme_cancel_request(struct request *req, void *data, bool reserved)
 {
 	dev_dbg_ratelimited(((struct nvme_ctrl *) data)->device,
diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index cedf9b31898673..5dfd806fc2d28c 100644
--- a/drivers/nvme/host/fabrics.c
+++ b/drivers/nvme/host/fabrics.c
@@ -552,11 +552,7 @@ blk_status_t nvmf_fail_nonready_command(struct nvme_ctrl *ctrl,
 	    !test_bit(NVME_CTRL_FAILFAST_EXPIRED, &ctrl->flags) &&
 	    !blk_noretry_request(rq) && !(rq->cmd_flags & REQ_NVME_MPATH))
 		return BLK_STS_RESOURCE;
-
-	nvme_req(rq)->status = NVME_SC_HOST_PATH_ERROR;
-	blk_mq_set_request_complete(rq);
-	nvme_complete_rq(rq);
-	return BLK_STS_OK;
+	return nvme_host_path_error(rq);
 }
 EXPORT_SYMBOL_GPL(nvmf_fail_nonready_command);
 
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index a72f0718109100..5819f038104149 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -575,6 +575,7 @@ static inline bool nvme_is_aen_req(u16 qid, __u16 command_id)
 }
 
 void nvme_complete_rq(struct request *req);
+blk_status_t nvme_host_path_error(struct request *req);
 bool nvme_cancel_request(struct request *req, void *data, bool reserved);
 void nvme_cancel_tagset(struct nvme_ctrl *ctrl);
 void nvme_cancel_admin_tagset(struct nvme_ctrl *ctrl);
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 6993efb27b39f0..f51af5e4970a2b 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -2091,16 +2091,6 @@ static blk_status_t nvme_rdma_queue_rq(struct blk_mq_hw_ctx *hctx,
 	err = nvme_rdma_post_send(queue, sqe, req->sge, req->num_sge,
 			req->mr ? &req->reg_wr.wr : NULL);
 	if (unlikely(err)) {
-		if (err == -EIO) {
-			/*
-			 * Fail the reqest so upper layer can failover I/O
-			 * if another path is available
-			 */
-			req->status = NVME_SC_HOST_PATH_ERROR;
-			blk_mq_set_request_complete(rq);
-			nvme_rdma_complete_rq(rq);
-			return BLK_STS_OK;
-		}
 		goto err_unmap;
 	}
 
@@ -2109,7 +2099,9 @@ static blk_status_t nvme_rdma_queue_rq(struct blk_mq_hw_ctx *hctx,
 err_unmap:
 	nvme_rdma_unmap_data(queue, rq);
 err:
-	if (err == -ENOMEM || err == -EAGAIN)
+	if (err == -EIO)
+		ret = nvme_host_path_error(rq);
+	else if (err == -ENOMEM || err == -EAGAIN)
 		ret = BLK_STS_RESOURCE;
 	else
 		ret = BLK_STS_IOERR;