[PATCH v3 0/8] block,md,nvme: correct handling of unsupported P2PDMA transfers

md treats an unsupported P2PDMA transfer to a member as success, and
nvme-rdma retries one forever.  Restore BLK_STS_TARGET for these
failures (lost in the blk_rq_dma_map conversion, v6.17) and fix what
md and nvme-rdma do around it.

Whether peer memory can be DMA-mapped depends on the PCIe topology
between the two devices: the same buffer may map fine for one
array member or nvme path and fail for another.  Since v6.17 that
failure completes as BLK_STS_INVAL.

md deliberately ignores INVAL member failures (commit
f7b24c7b41f2) and accepts P2PDMA bios since v7.2-rc1.  So a peer
write to an unreachable member simply counts as written: mirrors
silently diverge, and with no member reachable the write still
reports success.  nvme-rdma never even sees the errno --
ib_dma_map_sg() returns 0 -- and reports a path error, which
default multipath requeues forever.

  1  blk-mq-dma: restore BLK_STS_TARGET (block; stable, v6.17)
  2  md: keep REQ_NOMERGE on P2PDMA bios
  3  md/raid1: serialize non-write-behind writes on CollisionCheck
     rdevs (pre-existing bug patch 4 would widen; stable)
  4  md/raid1: no write-behind for P2PDMA bios
  5  md/raid1,raid10: keep REQ_NOMERGE on narrow_write_error()
     retry clones
  6  md/raid1: skip futile retries on P2PDMA mapping failures
  7  md/raid10: same
  8  nvme-rdma: preserve the DMA errno, return BLK_STS_TARGET
     (stable, v7.1)

Routing: patch 1 block, 2-7 md, 8 nvme; independently applicable
(patch 8 takes the errno from dma_map_sgtable() in rdma.c, not
from patch 1).

The patches were developed with AI assistance (see the Assisted-by
trailers); all code was human-reviewed and tested (result tables in
the v2 cover, linked below).

Against v7.2-rc2; merges clean onto current master.

Changes in v3:
 - split the raid1,raid10 mapping-failure patch per personality and
   folded its completion-path checks into one branch (Logan)
 - much shorter commit messages, comments and cover (Christoph,
   Keith, Leon); repro description added (Christoph)
 - picked up Logan's Reviewed-by on 1, 2, 4 and 5; since his review
   only a code comment in 1 and 2 was shortened (no code change)

Changes in v2: new serialization fix (patch 3), submission-time
state bit, metadata scatterlist, WantReplacement dropped for
mapping failures -- details in the v2 cover.

Link: https://lore.kernel.org/linux-raid/[email protected]/ [v1]
Link: https://lore.kernel.org/linux-raid/[email protected]/ [v2]

Mykola Marzhan (8):
  blk-mq-dma: restore BLK_STS_TARGET for unsupported P2P transfers
  md: ensure REQ_NOMERGE is set on P2PDMA bios
  md/raid1: serialize non-write-behind writes on CollisionCheck rdevs
  md/raid1: don't use write-behind for P2PDMA bios
  md/raid1,raid10: keep REQ_NOMERGE on narrow_write_error() retry clones
  md/raid1: skip futile retries on P2PDMA mapping failures
  md/raid10: skip futile retries on P2PDMA mapping failures
  nvme-rdma: return BLK_STS_TARGET for unsupported P2P transfers

 block/blk-mq-dma.c       |  6 +++-
 drivers/md/md.c          | 10 ++++--
 drivers/md/md.h          | 15 +++++++++
 drivers/md/raid1.c       | 73 ++++++++++++++++++++++++++++++----------
 drivers/md/raid1.h       |  2 ++
 drivers/md/raid10.c      | 66 +++++++++++++++++++++++++++---------
 drivers/md/raid10.h      |  2 ++
 drivers/nvme/host/rdma.c | 38 ++++++++++++---------
 8 files changed, 160 insertions(+), 52 deletions(-)


base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda
-- 
2.52.0