Comment 0 for bug 1813727

Starting with kernel 4.15.0-44 ext4 filesystem with meta_bg feature enabled can no longer be mounted.

Steps to reproduce:

- create two empty file and setup loopback devices on these files
dd if=/dev/zero of=/loop1 bs=1M count=50
losetup /dev/loop1 /loop1
dd if=/dev/zero of=/loop2 bs=1M count=50
losetup /dev/loop2 /loop2

- create a ext4 fs with meta_bg enabled on loop1:

mkfs.ext4 -O ^resize_inode,+meta_bg /dev/loop1

- create a ext4 fs without any options on loop2:

mkfs.ext4 /dev/loop2

- try to mount the filesystems

mkdir /mnt/loop1
mkdir /mnt/loop2
mount /dev/loop1 /mnt/loop1
mount /dev/loop1 /mnt/loop2

Expected behaviour:
All mounts succeed without error.

Actual behaviour:

root@xubu-18-04:~# mount /dev/loop1 /mnt/loop1
mount: /mnt/loop1: mount(2) system call failed: Structure needs cleaning.

See also a similar bug in fedora and debian:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903838

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903838

with a suspected patch by Theodore Ts'o to fix the issue: (Not tested)

https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=903838;filename=ext4-fix-false-negatives-and-false-positives-in-ext4.patch;msg=26

Additional info:

root@xubu-18-04:~# lsb_release -rd
Description: Ubuntu 18.04.1 LTS
Release: 18.04

root@xubu-18-04:~# apt-cache policy linux-image-generic
linux-image-generic:
  Installed: 4.15.0.44.46
  Candidate: 4.15.0.44.46
  Version table:
 *** 4.15.0.44.46 500
        500 http://de.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages
        100 /var/lib/dpkg/status
     4.15.0.20.23 500
        500 http://de.archive.ubuntu.com/ubuntu bionic/main amd64 Packages