[PATCH v6 0/2] Don't set MD_BROKEN on failfast bio failure

Changes from V5:
- Prevent md being broken when rdev has FailFast, regardless of the bios flag.
  Thanks to Xiao for the advice:
  https://lore.kernel.org/linux-raid/CALTww2_nJqyA99cG9YNarXEB4wimFK=pKy=qrxdkfB60PaUa1w@mail.gmail.com/#t (local)
- Dropping preparation refactor, flag rename, error logging improvement
  commits
Changes from V4:
- Use device_lock to serialize md_error() instead of adding a new
  spinlock_t.
- Rename new function md_bio_failure_error() to md_cond_error().
- Add helper function pers->should_error() to determine whether to fail
  rdev in failfast bio failure, instead of using the LastDev flag.
- Avoid changing the behavior of the LastDev flag.
- Drop fix for R{1,10}BIO_Uptodate not being set despite successful
  retry; this will be sent separately after Nan's refactor.
- Drop fix for the message 'Operation continuing on 0 devices'; as it is
  outside the scope of this patch, it will be sent separately.
- Improve logging when metadata writing fails.
- Rename LastDev to RetryingSBWrite.
Changes from V3:
- The error handling in md_error() is now serialized, and a new helper
  function, md_bio_failure_error, has been introduced.
- MD_FAILFAST bio failures are now processed by md_bio_failure_error
  instead of signaling via FailfastIOFailure.
- RAID10: Fix missing reschedule of failfast read bio failure
- Regardless of failfast, in narrow_write_error, writes that succeed
  in retry are returned to the higher layer as success
Changes from V2:
- Fix to prevent the array from being marked broken for all
  Failfast IOs, not just metadata.
- Reflecting the review, update raid{1,10}_error to clear
  FailfastIOFailure so that devices are properly marked Faulty.
Changes from V1:
- Avoid setting MD_BROKEN instead of clearing it
- Add pr_crit() when setting MD_BROKEN
- Fix the message may shown after all rdevs failure:
  "Operation continuing on 0 devices"

v5: https://lore.kernel.org/linux-raid/20251027150433.18193-1-k@mgml.me/ (local)
v4: https://lore.kernel.org/linux-raid/20250915034210.8533-1-k@mgml.me/ (local)
v3: https://lore.kernel.org/linux-raid/20250828163216.4225-1-k@mgml.me/ (local)
v2: https://lore.kernel.org/linux-raid/20250817172710.4892-1-k@mgml.me/ (local)
v1: https://lore.kernel.org/linux-raid/20250812090119.153697-1-k@mgml.me/ (local)

When multiple MD_FAILFAST bios fail simultaneously on Failfast-enabled
rdevs in RAID1/RAID10, the following issues can occur:
* MD_BROKEN is set and the array halts, even though this should not occur
  under the intended Failfast design.
* Writes retried through narrow_write_error succeed, but the I/O is still
  reported as BLK_STS_IOERR
  * NOTE: a fix for this was removed in v5, will be send separetely
    https://lore.kernel.org/linux-raid/6f0f9730-4bbe-7f3c-1b50-690bb77d5d90@huaweicloud.com/ (local)
* RAID10 only: If a Failfast read I/O fails, it is not retried on any
  remaining rdev, and as a result, the upper layer receives an I/O error.

Simultaneous bio failures across multiple rdevs are uncommon; however,
rdevs serviced via nvme-tcp can still experience them due to something as
simple as an Ethernet fault. The issue can be reproduced using the
following steps.

# prepare nvmet/nvme-tcp and md array 
sh-5.2# cat << 'EOF' > loopback-nvme.sh
set -eu
nqn="nqn.2025-08.io.example:nvmet-test-$1"
back=$2
cd /sys/kernel/config/nvmet/
mkdir subsystems/$nqn
echo 1 > subsystems/${nqn}/attr_allow_any_host
mkdir subsystems/${nqn}/namespaces/1
echo -n ${back} > subsystems/${nqn}/namespaces/1/device_path
echo 1 > subsystems/${nqn}/namespaces/1/enable
ports="ports/1"
if [ ! -d $ports ]; then
        mkdir $ports
        cd $ports
        echo 127.0.0.1 > addr_traddr
        echo tcp       > addr_trtype
        echo 4420      > addr_trsvcid
        echo ipv4      > addr_adrfam
        cd ../../
fi
ln -s /sys/kernel/config/nvmet/subsystems/${nqn} ${ports}/subsystems/
nvme connect -t tcp -n $nqn -a 127.0.0.1 -s 4420
EOF

sh-5.2# chmod +x loopback-nvme.sh
sh-5.2# modprobe -a nvme-tcp nvmet-tcp
sh-5.2# truncate -s 1g a.img b.img
sh-5.2# losetup --show -f a.img
/dev/loop0
sh-5.2# losetup --show -f b.img
/dev/loop1
sh-5.2# ./loopback-nvme.sh 0 /dev/loop0
connecting to device: nvme0
sh-5.2# ./loopback-nvme.sh 1 /dev/loop1
connecting to device: nvme1
sh-5.2# mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 \
--failfast /dev/nvme0n1 --failfast /dev/nvme1n1
...
mdadm: array /dev/md0 started.

# run fio 
sh-5.2# fio --name=test --filename=/dev/md0 --rw=randrw --rwmixread=50 \
--bs=4k --numjobs=9 --time_based --runtime=300s --group_reporting --direct=1 &

# It can reproduce the issue by block nvme traffic during fio
sh-5.2# iptables -A INPUT -m tcp -p tcp --dport 4420 -j DROP;
sh-5.2# sleep 10; # twice the default KATO value
sh-5.2# iptables -D INPUT -m tcp -p tcp --dport 4420 -j DROP


Patch 1 prevent array broken when FailFast is set on rdev
Patch 2 adds the missing retry path for Failfast read errors in RAID10.

Kenta Akagi (2):
  md: Don't set MD_BROKEN for RAID1 and RAID10 when using FailFast
  md/raid10: fix failfast read error not rescheduled

 drivers/md/md.c     |  6 ++++--
 drivers/md/raid1.c  |  8 +++++++-
 drivers/md/raid10.c | 15 ++++++++++++++-
 3 files changed, 25 insertions(+), 4 deletions(-)

-- 
2.50.1