[PATCH v2 7/7] nvme-rdma: return BLK_STS_TARGET for unsupported P2P transfers
Mykola Marzhan
mykola at meshstor.io
Sun Jul 19 03:53:27 PDT 2026
Since commit 23528aa3320a ("nvme: enable PCI P2PDMA support for RDMA
transport") nvme-rdma accepts P2PDMA bios, but a mapping failure for
peer memory the HCA cannot reach is misreported as a path error:
ib_dma_map_sg() returns 0, discarding the -EREMOTEIO that
dma_map_sgtable() documents for exactly this case, and the driver
converts it to -EIO -> nvme_host_path_error().
Under the default multipath configuration (the multipath head node
advertises BLK_FEAT_PCI_P2PDMA since commit fb0eeeed91f3
("nvme-multipath: enable PCI P2PDMA for multipath devices")) the
path-error status makes nvme_failover_req() requeue the bios with a
fresh retry budget each cycle, and since the mapping failure is a
deterministic property of the peer/device pairing the I/O simply
never completes: a hot requeue livelock, and a stacked md mirror
hangs instead of failing over to its other leg. With
nvme_core.multipath=N the request burns nvme_max_retries requeues --
nothing ever reaching the wire -- and completes as
BLK_STS_TRANSPORT, which blk_path_error() classifies as retryable
and md/raid1,raid10 treat as a genuine device error: retry storms on
writes, read-error-budget eviction of a healthy member on reads (see
the preceding md patches, whose mapping-failure handling keys on
BLK_STS_TARGET).
Map both the data and the metadata scatterlists with
ib_dma_map_sgtable_attrs() so the DMA layer's error code is
preserved, and translate -EREMOTEIO to BLK_STS_TARGET: the
classification nvme-pci established in commit 91fb2b6052f7
("nvme-pci: convert to using dma_map_sgtable()") and the preceding
blk-mq-dma patch restores. The metadata path needs the same
treatment because integrity buffers are not always host memory:
bio_integrity_map_user() allows P2P pages whenever the queue
advertises P2PDMA, and nvme-pci already maps P2P metadata.
Returning BLK_STS_TARGET from queue_rq is a deliberate trade-off: it
forecloses failover for a configuration where a sibling path through
a different HCA could reach the peer. This matches nvme-pci, which
has returned BLK_STS_TARGET for unsupported P2P mappings since
that same commit and equally forecloses cross-controller failover;
distinguishing this-path-unreachable from all-paths-unreachable at
completion time would cost a spurious requeue cycle per I/O, and a
stacking consumer (md) routes around the leg one layer up.
Start the request only after mapping succeeds, as nvme-pci does: a
mapping failure now errors out of queue_rq on a not-yet-started
request, so nvme_mpath_start_request() accounting is never taken and
cannot leak on the direct blk-mq completion (this also closes the same
latent leak for mapping-failure BLK_STS_IOERR returns; the post-send
error tail is untouched). A mapping -ENOMEM now takes the existing
BLK_STS_RESOURCE branch instead of masquerading as a path error, and a
DMA-layer -EINVAL completes as BLK_STS_IOERR instead of a path error;
generic -EIO keeps today's host-path-error behavior, and virt-DMA
devices are unaffected. Ratelimit the map-failure message -- with an md
mirror steering peer-memory I/O around an unreachable leg it fires per
redirected I/O, not per rare event.
Fixes: 23528aa3320a ("nvme: enable PCI P2PDMA support for RDMA transport")
Cc: stable at vger.kernel.org # v7.1
Assisted-by: Claude:claude-fable-5
Signed-off-by: Mykola Marzhan <mykola at meshstor.io>
---
drivers/nvme/host/rdma.c | 42 +++++++++++++++++++++++++---------------
1 file changed, 26 insertions(+), 16 deletions(-)
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 6909e3542794..9017d927edc4 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -1469,6 +1469,7 @@ static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
int *count, int *pi_count)
{
struct nvme_rdma_request *req = blk_mq_rq_to_pdu(rq);
+ struct sg_table sgt;
int ret;
req->data_sgl.sg_table.sgl = (struct scatterlist *)(req + 1);
@@ -1480,12 +1481,14 @@ static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
req->data_sgl.nents = blk_rq_map_sg(rq, req->data_sgl.sg_table.sgl);
- *count = ib_dma_map_sg(ibdev, req->data_sgl.sg_table.sgl,
- req->data_sgl.nents, rq_dma_dir(rq));
- if (unlikely(*count <= 0)) {
- ret = -EIO;
+ sgt = (struct sg_table) {
+ .sgl = req->data_sgl.sg_table.sgl,
+ .orig_nents = req->data_sgl.nents,
+ };
+ ret = ib_dma_map_sgtable_attrs(ibdev, &sgt, rq_dma_dir(rq), 0);
+ if (unlikely(ret))
goto out_free_table;
- }
+ *count = sgt.nents;
if (blk_integrity_rq(rq)) {
req->metadata_sgl->sg_table.sgl =
@@ -1501,14 +1504,14 @@ static int nvme_rdma_dma_map_req(struct ib_device *ibdev, struct request *rq,
req->metadata_sgl->nents = blk_rq_map_integrity_sg(rq,
req->metadata_sgl->sg_table.sgl);
- *pi_count = ib_dma_map_sg(ibdev,
- req->metadata_sgl->sg_table.sgl,
- req->metadata_sgl->nents,
- rq_dma_dir(rq));
- if (unlikely(*pi_count <= 0)) {
- ret = -EIO;
+ sgt = (struct sg_table) {
+ .sgl = req->metadata_sgl->sg_table.sgl,
+ .orig_nents = req->metadata_sgl->nents,
+ };
+ ret = ib_dma_map_sgtable_attrs(ibdev, &sgt, rq_dma_dir(rq), 0);
+ if (unlikely(ret))
goto out_free_pi_table;
- }
+ *pi_count = sgt.nents;
}
return 0;
@@ -2026,8 +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 ||
@@ -2039,11 +2040,13 @@ static blk_status_t nvme_rdma_queue_rq(struct blk_mq_hw_ctx *hctx,
err = nvme_rdma_map_data(queue, rq, c);
if (unlikely(err < 0)) {
- dev_err(queue->ctrl->ctrl.device,
- "Failed to map data (%d)\n", err);
+ dev_err_ratelimited(queue->ctrl->ctrl.device,
+ "Failed to map data (%d)\n", err);
goto err;
}
+ nvme_start_request(rq);
+
sqe->cqe.done = nvme_rdma_send_done;
ib_dma_sync_single_for_device(dev, sqe->dma,
@@ -2063,6 +2066,13 @@ 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;
+ /*
+ * The DMA layer refused to map peer memory to this device: a
+ * property of the pairing, not a path failure. Match nvme-pci
+ * and do not retry (see blk_path_error()).
+ */
+ else if (err == -EREMOTEIO)
+ ret = BLK_STS_TARGET;
else
ret = BLK_STS_IOERR;
nvme_cleanup_cmd(rq);
--
2.43.0
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