nvme-multipath: set BIO_REMAPPED on bios remapped to per-path namespace disks

When nvme_ns_head_submit_bio() remaps a bio from the multipath head to a
per-path namespace, bio_set_dev() clears BIO_REMAPPED.  The remapped bio
is then resubmitted through submit_bio_noacct() which calls
bio_check_eod() because BIO_REMAPPED is not set.

This races with nvme_ns_remove() which zeroes the per-path capacity
before synchronize_srcu():

  CPU 0 (IO submission)
  ---------------------
  srcu_read_lock()
  nvme_find_path() -> ns
    [NVME_NS_READY is set]

  CPU 1 (namespace removal)
  -------------------------
  clear_bit(NVME_NS_READY)
  set_capacity(ns->disk, 0)
  synchronize_srcu()  <- blocks

  CPU 0 (IO submission)
  ---------------------
  bio_set_dev(bio, ns->disk->part0)
    [clears BIO_REMAPPED]
  submit_bio_noacct(bio)
    -> bio_check_eod() sees capacity=0
    -> bio fails with IO error

The SRCU read lock prevents synchronize_srcu() from completing, but does
not prevent set_capacity(0) from executing.  The bio fails the EOD check
before it reaches the NVMe driver, so nvme_failover_req() never gets a
chance to redirect it to another path of multipath.  IO errors are
reported to the application despite another path being available.

On older kernels (before commit 0b64682 "block: skip unnecessary
checks for split bio"), the same race was also reachable through split
remainders resubmitted via submit_bio_noacct().

Fix this by setting BIO_REMAPPED after bio_set_dev() in
nvme_ns_head_submit_bio().  This skips bio_check_eod() on the per-path
device; the EOD check already passed on the multipath head.

NVMe per-path namespace devices are always whole disks (bd_partno=0), so
the blk_partition_remap() skip also gated by BIO_REMAPPED is a no-op.
The flag does not persist across failover and cannot go stale if the
namespace geometry changes between attempts: nvme_failover_req() calls
bio_set_dev() to redirect the bio back to the multipath head, which
clears BIO_REMAPPED.  When nvme_requeue_work() resubmits through
submit_bio_noacct(), bio_check_eod() runs normally against the current
capacity.

Same approach as commit 3a905c3 ("block: skip bio_check_eod for
partition-remapped bios").

Fixes: a7c7f7b ("nvme: use bio_set_dev to assign ->bi_bdev")
Cc: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Igor Achkinazi <igor.achkinazi@dell.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

Author: Achkinazi, Igor

drivers/nvme/host/multipath.c

@@ -521,6 +521,12 @@ static void nvme_ns_head_submit_bio(struct bio *bio)
 	ns = nvme_find_path(head);
 	if (likely(ns)) {
 		bio_set_dev(bio, ns->disk->part0);
+		/*
+		 * Use BIO_REMAPPED to skip bio_check_eod() when this bio
+		 * enters submit_bio_noacct() for the per-path device. The EOD
+		 * check already passed on the multipath head.
+		 */
+		bio_set_flag(bio, BIO_REMAPPED);
 		bio->bi_opf |= REQ_NVME_MPATH;
 		trace_block_bio_remap(bio, disk_devt(ns->head->disk),
 				      bio->bi_iter.bi_sector);