[PATCH v6 10/12] nvme-rdma: return BLK_STS_P2PDMA for unsupported P2P transfers

A P2P transfer the PCIe topology cannot route fails DMA mapping
with -EREMOTEIO.  nvme-rdma folds every mapping error into -EIO, a
retryable host-path error: multipath requeues the I/O forever, a
single path burns its whole retry budget.

Propagate the real error code and return the unroutable case as the
non-retryable BLK_STS_P2PDMA.  As in nvme-pci, -ENOMEM now requeues
(BLK_STS_RESOURCE) and -EINVAL fails (BLK_STS_IOERR); -EIO stays a
retryable host-path error.

Start the request only after the mapping succeeds, as nvme-pci and
nvme-tcp do.  A hard status from ->queue_rq is completed by blk-mq
itself, skipping nvme_mpath_end_request(), so the multipath I/O
accounting leaks -- today for -EINVAL, and now for BLK_STS_P2PDMA.

Fixes: 23528aa3320a ("nvme: enable PCI P2PDMA support for RDMA transport")
Cc: [email protected] # v7.1: requires BLK_STS_P2PDMA and the ib_dma_map_sgtable_attrs() conversion
Assisted-by: Claude:claude-fable-5
Signed-off-by: Mykola Marzhan <[email protected]>
Reviewed-by: Logan Gunthorpe <[email protected]>
---
 drivers/nvme/host/rdma.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 63830334c73e..c38d949502b7 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -1486,10 +1486,8 @@ static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
 		.orig_nents	= req->data_sgl.nents,
 	};
 	ret = ib_dma_map_sgtable_attrs(ibdev, &sgt, rq_dma_dir(rq), 0);
-	if (unlikely(ret)) {
-		ret = -EIO;
+	if (unlikely(ret))
 		goto out_free_table;
-	}
 	*count = sgt.nents;
 
 	if (blk_integrity_rq(rq)) {
@@ -1511,10 +1509,8 @@ static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
 			.orig_nents	= req->metadata_sgl->nents,
 		};
 		ret = ib_dma_map_sgtable_attrs(ibdev, &sgt, rq_dma_dir(rq), 0);
-		if (unlikely(ret)) {
-			ret = -EIO;
+		if (unlikely(ret))
 			goto out_free_pi_table;
-		}
 		*pi_count = sgt.nents;
 	}
 
@@ -2033,8 +2029,6 @@ static blk_status_t nvme_rdma_queue_rq(struct blk_mq_hw_ctx *hctx,
 	if (ret)
 		goto unmap_qe;
 
-	nvme_start_request(rq);
-
 	if (IS_ENABLED(CONFIG_BLK_DEV_INTEGRITY) &&
 	    queue->pi_support &&
 	    (c->common.opcode == nvme_cmd_write ||
@@ -2051,6 +2045,8 @@ static blk_status_t nvme_rdma_queue_rq(struct blk_mq_hw_ctx *hctx,
 		goto err;
 	}
 
+	nvme_start_request(rq);
+
 	sqe->cqe.done = nvme_rdma_send_done;
 
 	ib_dma_sync_single_for_device(dev, sqe->dma,
@@ -2070,6 +2066,9 @@ static blk_status_t nvme_rdma_queue_rq(struct blk_mq_hw_ctx *hctx,
 		ret = nvme_host_path_error(rq);
 	else if (err == -ENOMEM || err == -EAGAIN)
 		ret = BLK_STS_RESOURCE;
+	/* Peer memory unreachable from this device: don't retry. */
+	else if (err == -EREMOTEIO)
+		ret = BLK_STS_P2PDMA;
 	else
 		ret = BLK_STS_IOERR;
 	nvme_cleanup_cmd(rq);
-- 
2.52.0