[Bug 2036467] Re: Resizing cloud-images occasionally fails due to superblock checksum mismatch in resize2fs

[Krister Johansen]

Hi Matthew,
Thanks for the update. I'm glad this finally reproduced in your environment.  I don't have a great explanation for why it took so much longer there.  I did observe that it seemed more likely to occur in us-west-2 during the 9a-5p window in the local timezone. The timing may be subtly affected by overall EBS utilization.  Just a guess, though.

Thanks again,

-K

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https://bugs.launchpad.net/bugs/2036467

Title:
  Resizing cloud-images occasionally fails due to superblock checksum
  mismatch in resize2fs

Status in cloud-images:
  New
Status in e2fsprogs package in Ubuntu:
  In Progress
Status in e2fsprogs source package in Trusty:
  Won't Fix
Status in e2fsprogs source package in Xenial:
  Won't Fix
Status in e2fsprogs source package in Bionic:
  Won't Fix
Status in e2fsprogs source package in Focal:
  In Progress
Status in e2fsprogs source package in Jammy:
  In Progress
Status in e2fsprogs source package in Lunar:
  Won't Fix
Status in e2fsprogs source package in Mantic:
  In Progress

Bug description:
  [Impact]

  This is a long running bug plaguing cloud-images, where on a rare
  occasion resize2fs would fail and the image would not resize to fit
  the entire disk.

  Online resizes would fail due to a superblock checksum mismatch, where
  the superblock in memory differs from what is currently on disk due to
  changes made to the image.

  $ resize2fs /dev/nvme1n1p1
  resize2fs 1.47.0 (5-Feb-2023)
  resize2fs: Superblock checksum does not match superblock while trying to open /dev/nvme1n1p1
  Couldn't find valid filesystem superblock.

  Changing the read of the superblock to Direct I/O solves the issue.

  [Testcase]

  Start an c5.large instance on AWS, and attach a 60gb gp3 volume for
  use as a scratch disk.

  Run the following script, courtesy of Krister Johansen and his team:

     #!/usr/bin/bash
     set -euxo pipefail

     while true
     do
             parted /dev/nvme1n1 mklabel gpt mkpart primary 2048s 2099200s
             sleep .5
             mkfs.ext4 /dev/nvme1n1p1
             mount -t ext4 /dev/nvme1n1p1 /mnt
             stress-ng --temp-path /mnt -D 4 &
             STRESS_PID=$!
             sleep 1
             growpart /dev/nvme1n1 1
             resize2fs /dev/nvme1n1p1
             kill $STRESS_PID
             wait $STRESS_PID
             umount /mnt
             wipefs -a /dev/nvme1n1p1
             wipefs -a /dev/nvme1n1
     done

  Test packages are available in the following ppa:

  https://launchpad.net/~mruffell/+archive/ubuntu/lp2036467-test

  If you install the test packages, the race no longer occurs.

  [Where problems could occur]

  We are changing how resize2fs reads the superblock from underlying
  disks.

  If a regression were to occur, resize2fs could fail to resize offline
  or online volumes. As all cloud-images are online resized during their
  initial boot, this could have a large impact to public and private
  clouds should a regression occur.

  [Other info]

  Upstream mailing list discussion:
  https://lore.kernel.org/linux-ext4/20230605225221.GA5737@templeofstupid.com/
  https://lore.kernel.org/linux-ext4/20230609042239.GA1436857@mit.edu/

  This was fixed in the below commit upstream:

  commit 43a498e938887956f393b5e45ea6ac79cc5f4b84
  Author: Theodore Ts'o <tytso at mit.edu>
  Date: Thu, 15 Jun 2023 00:17:01 -0400
  Subject: resize2fs: use Direct I/O when reading the superblock for
   online resizes
  Link: https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/commit/?id=43a498e938887956f393b5e45ea6ac79cc5f4b84

  The commit has not been tagged to any release. All supported Ubuntu
  releases require this fix, and need to be published in standard non-
  ESM archives to be picked up in cloud images.

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