[Bug 1381968] [NEW] Fstrim destroys data on loopback device

[JDownloader]

Public bug reported:

I've upgraded Ubuntu Server 12.04 LTS to 14.04 LTS.

The setup contains a loopback device (/dev/loop3) mounted into a
software raid 1 (/dev/md2).

After the weekly cronjob (/etc/cron.weekly/fstrim) ran, I've discovered
that it wiped all data on the loopback device from the raid.

fstrim-all skips check because the loopback device is part of device mapper raid.
if [ "${REALDEV#/dev/dm-}" != "$REALDEV" ]; then
        echo "device $DEV is on devmapper, skipping TRIM feature check"

Issue can be reproduced on raid setup and plain loopback mount setup!

Here is step-by-step how to reproduce the issue:

1.) create sparse image file
dd of=/sparse-file bs=1k seek=1024000

2.) losetup loopback device
losetup /dev/loop3 /sparse-file

3.) create raid1
mdadm --create /dev/md2 --auto md --level=1 --raid-devices=1 /dev/loop3

4.) create fs
mkfs.ext4 /dev/md2

4.1.) check sparse-file size
ls -lash /sparse-file

5.) mount and copy data
mount /dev/md2 /mnt
copy some random files on /mnt

5.1.) check sparse-file size again
ls -lash /sparse-file -> size indicates it contains the copied data

6.) destroy loopback via fstrim
fstrim -v /mnt

7.) data is wiped
umount /mnt
ls -lash /sparse-file -> size indicates that all data is wiped out!
fsck -v -f /dev/md2 -> will report infinite errors on filesystem

I could not find any similiar bugreport.

Best Regards
Daniel

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Confirmed


** Tags: dataloss fstrim kernel-bug loopback

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https://bugs.launchpad.net/bugs/1381968

Title:
  Fstrim destroys data on loopback device

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  I've upgraded Ubuntu Server 12.04 LTS to 14.04 LTS.

  The setup contains a loopback device (/dev/loop3) mounted into a
  software raid 1 (/dev/md2).

  After the weekly cronjob (/etc/cron.weekly/fstrim) ran, I've
  discovered that it wiped all data on the loopback device from the
  raid.

  fstrim-all skips check because the loopback device is part of device mapper raid.
  if [ "${REALDEV#/dev/dm-}" != "$REALDEV" ]; then
          echo "device $DEV is on devmapper, skipping TRIM feature check"

  Issue can be reproduced on raid setup and plain loopback mount setup!

  Here is step-by-step how to reproduce the issue:

  1.) create sparse image file
  dd of=/sparse-file bs=1k seek=1024000

  2.) losetup loopback device
  losetup /dev/loop3 /sparse-file

  3.) create raid1
  mdadm --create /dev/md2 --auto md --level=1 --raid-devices=1 /dev/loop3

  4.) create fs
  mkfs.ext4 /dev/md2

  4.1.) check sparse-file size
  ls -lash /sparse-file

  5.) mount and copy data
  mount /dev/md2 /mnt
  copy some random files on /mnt

  5.1.) check sparse-file size again
  ls -lash /sparse-file -> size indicates it contains the copied data

  6.) destroy loopback via fstrim
  fstrim -v /mnt

  7.) data is wiped
  umount /mnt
  ls -lash /sparse-file -> size indicates that all data is wiped out!
  fsck -v -f /dev/md2 -> will report infinite errors on filesystem

  I could not find any similiar bugreport.

  Best Regards
  Daniel

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