Hello, I recently backported the following patches into the Ubuntu stable kernels: md: add md_submit_discard_bio() for submitting discard bio md/raid10: extend r10bio devs to raid disks md/raid10: pull codes that wait for blocked dev into one function md/raid10: improve raid10 discard request md/raid10: improve discard request for far layout dm raid: fix discard limits for raid1 and raid10 dm raid: remove unnecessary discard limits for raid10 and this morning, a user reported the following downstream bug: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1907262/ Their weekly cronjob that runs fstrim had run, and their raid10 array has extensive data corruption. The issue is reproducible on the latest 5.10-rc7 mainline kernel, steps are below. I used a m5d.4xlarge instance on AWS to ultilise 2x 300GB SSDs that support block discard. You will want to select small disks to lower the time needed to reproduce. $ uname -rv 5.10.0-rc7+ #1 SMP Wed Dec 9 01:15:27 UTC 2020 Create a raid10 array, with LVM: $ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT nvme0n1 259:0 0 8G 0 disk └─nvme0n1p1 259:1 0 8G 0 part / nvme1n1 259:2 0 279.4G 0 disk nvme2n1 259:3 0 279.4G 0 disk $ sudo -s # mdadm -C -v -l10 -n2 -N "lv-raid" -R /dev/md0 /dev/nvme1n1 /dev/nvme2n1 mdadm: layout defaults to n2 mdadm: layout defaults to n2 mdadm: chunk size defaults to 512K mdadm: size set to 292836352K mdadm: automatically enabling write-intent bitmap on large array mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md0 started. # pvcreate -ff -y /dev/md0 Physical volume "/dev/md0" successfully created. # vgcreate -f -y VolGroup /dev/md0 Volume group "VolGroup" successfully created # lvcreate -n root -L 100G -ay -y VolGroup Logical volume "root" created. # mkfs.ext4 /dev/VolGroup/root mke2fs 1.44.1 (24-Mar-2018) Discarding device blocks: done Creating filesystem with 26214400 4k blocks and 6553600 inodes Filesystem UUID: d7be2e14-fa4d-4489-884b-3bef63b1e1db Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000, 23887872 Allocating group tables: done Writing inode tables: done Creating journal (131072 blocks): done Writing superblocks and filesystem accounting information: done # mount /dev/VolGroup/root /mnt Next, wait for the disk check to complete, 25 minutes on m5d.4xlarge instance. # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 nvme2n1[1] nvme1n1[0] 292836352 blocks super 1.2 2 near-copies [2/2] [UU] [==>..................] resync = 12.0% (35211392/292836352) finish=21.4min speed=200340K/sec bitmap: 3/3 pages [12KB], 65536KB chunk unused devices: <none> # cat /sys/block/md0/md/mismatch_cnt 76918016 # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 nvme2n1[1] nvme1n1[0] 292836352 blocks super 1.2 2 near-copies [2/2] [UU] bitmap: 0/3 pages [0KB], 65536KB chunk unused devices: <none> # cat /sys/block/md0/md/mismatch_cnt 582330240 Now that the check is complete, create a file, sync and delete it: # dd if=/dev/zero of=/mnt/data.raw bs=4K count=1M 1048576+0 records in 1048576+0 records out 4294967296 bytes (4.3 GB, 4.0 GiB) copied, 3.95974 s, 1.1 GB/s # sync # rm /mnt/data.raw Perform a check: # echo check > /sys/block/md0/md/sync_action Again, wait 25 minutes for it to complete: # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 nvme1n1[1] nvme2n1[0] 292836352 blocks super 1.2 2 near-copies [2/2] [UU] [==>..................] check = 13.7% (40356224/292836352) finish=20.8min speed=201707K/sec bitmap: 0/3 pages [0KB], 65536KB chunk unused devices: <none> # cat /sys/block/md0/md/mismatch_cnt 1469696 # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 nvme1n1[1] nvme2n1[0] 292836352 blocks super 1.2 2 near-copies [2/2] [UU] bitmap: 0/3 pages [0KB], 65536KB chunk unused devices: <none> # cat /sys/block/md0/md/mismatch_cnt 1469696 Now, perform the fstrim: # fstrim /mnt --verbose /mnt: 97.9 GiB (105089236992 bytes) trimmed Go for another check: # echo check >/sys/block/md0/md/sync_action # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 nvme1n1[1] nvme2n1[0] 292836352 blocks super 1.2 2 near-copies [2/2] [UU] [========>............] check = 40.3% (118270848/292836352) finish=14.4min speed=200963K/sec bitmap: 0/3 pages [0KB], 65536KB chunk unused devices: <none> # cat /sys/block/md0/md/mismatch_cnt 205324928 # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid10 nvme1n1[1] nvme2n1[0] 292836352 blocks super 1.2 2 near-copies [2/2] [UU] bitmap: 0/3 pages [0KB], 65536KB chunk unused devices: <none> # cat /sys/block/md0/md/mismatch_cnt 205324928 Now, we need to take the raid10 array down, and perform a fsck on one disk at a time: # umount /mnt # vgchange -a n /dev/VolGroup 0 logical volume(s) in volume group "VolGroup" now active # mdadm --stop /dev/md0 mdadm: stopped /dev/md0 Let's do first disk; # mdadm --assemble /dev/md127 /dev/nvme1n1 mdadm: /dev/md1 assembled from 1 drive - need all 2 to start it (use --run to insist). # mdadm --run /dev/md127 mdadm: started array /dev/md/lv-raid # vgchange -a y /dev/VolGroup 1 logical volume(s) in volume group "VolGroup" now active # fsck.ext4 -n -f /dev/VolGroup/root e2fsck 1.44.1 (24-Mar-2018) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/VolGroup/root: 11/6553600 files (0.0% non-contiguous), 557848/26214400 blocks # vgchange -a n /dev/VolGroup 0 logical volume(s) in volume group "VolGroup" now active # mdadm --stop /dev/md127 mdadm: stopped /dev/md127 The second disk: # mdadm --assemble /dev/md127 /dev/nvme2n1 mdadm: /dev/md1 assembled from 1 drive - need all 2 to start it (use --run to insist). # mdadm --run /dev/md127 mdadm: started array /dev/md/lv-raid # vgchange -a y /dev/VolGroup 1 logical volume(s) in volume group "VolGroup" now active # fsck.ext4 -n -f /dev/VolGroup/root e2fsck 1.44.1 (24-Mar-2018) Resize inode not valid. Recreate? no Pass 1: Checking inodes, blocks, and sizes Inode 7 has illegal block(s). Clear? no Illegal indirect block (1714656753) in inode 7. IGNORED. Error while iterating over blocks in inode 7: Illegal indirect block found /dev/VolGroup/root: ********** WARNING: Filesystem still has errors ********** e2fsck: aborted /dev/VolGroup/root: ********** WARNING: Filesystem still has errors ********** # vgchange -a n /dev/VolGroup 0 logical volume(s) in volume group "VolGroup" now active # mdadm --stop /dev/md127 mdadm: stopped /dev/md127 There are no panics or anything in dmesg. The directory structure of the first disk is intact, but the second disk only has Lost+Found present. I can confirm it is the patches listed at the top of the email, but I have not had an opportunity to bisect to find the exact root cause. I will do that once we confirm what Ubuntu stable kernels are affected and begin reverting the patches. Let me know if you need any more details. Thanks, Matthew Ruffell
