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Bug 1530358

Summary: Running "vdo remove" for a non-existent device creates zero-byte regular file in old device path
Product: Red Hat Enterprise Linux 7 Reporter: Bryan Gurney <bgurney>
Component: vdoAssignee: Joseph Chapman <jochapma>
Status: CLOSED ERRATA QA Contact: Jakub Krysl <jkrysl>
Severity: unspecified Docs Contact:
Priority: high    
Version: 7.5CC: awalsh, jkrysl, jochapma, limershe, salmy
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: 6.1.0.137 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2018-04-10 15:49:25 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Bryan Gurney 2018-01-02 18:22:44 UTC
Description of problem:
If a VDO volume is created on a device, and that VDO volume is stopped, and the device is later removed from the system (perhaps because the VDO volume is not needed anymore, but the administrator forgot to run the "vdo remove" command prior to removing the backing storage device), a zero-byte regular file will be created with the same name of the device previously used to create the now-removed VDO volume.

Version-Release number of selected component (if applicable):
vdo-6.1.0.98-13.x86_64

How reproducible:
100% so far

Steps to Reproduce:
1. Create a VDO volume on a test device (example: /dev/sdb) using the command "vdo create --name=vdo1 --device=/dev/sdb".
2. Stop the VDO volume using the command "vdo stop --name=vdo1".
3. Remove the backing device from the system
4. Run "vdo remove --name=vdo1 --verbose".

Actual results:
The VDO volume is successfully removed, but a zero-byte regular file is left over in the path of the previous backing device:
# vdo remove --name=vdo1 --verbose
Removing VDO vdo1
Stopping VDO vdo1
    dmsetup status vdo1
    dd if=/dev/zero of=/dev/sdb oflag=direct bs=4096 count=1
vdo: ERROR - dd: failed to open ‘/dev/sdb’: Invalid argument

# ls -l /dev/sdb
-rw-r--r--. 1 root root 0 Jan  2 13:08 /dev/sdb

# vdo remove --name=vdo1 --verbose
vdo: ERROR - VDO volume vdo1 not found


Expected results:
The VDO volume is successfully removed.  No device file is created if it doesn't already exist.

Additional info:
If this regular file still exists, and the device (or another device) is reattached to the system without removing the zero-byte regular file, it will result in the failure to create a node for the device.  (This can be worked around by removing the zero-byte regular file, and running mknod to recreate it, or rebooting the system.)

Comment 2 Jakub Krysl 2018-01-03 10:29:28 UTC
Reproduced using VDO on LVM:
# vgcreate vg /dev/sde
  Physical volume "/dev/sde" successfully created.
  Volume group "vg" successfully created
# lvcreate --name lv vg -L 10G
  Logical volume "lv" created.
# vdo create --name vdo --device /dev/mapper/vg-lv
Creating VDO vdo
Starting VDO vdo
Starting compression on VDO vdo
VDO instance 137 volume is ready at /dev/mapper/vdo
# vdo stop --name vdo
Stopping VDO vdo
# vgremove vg -ff
  Logical volume "lv" successfully removed
  Volume group "vg" successfully removed
# vdo remove --name vdo --verbose
Removing VDO vdo
Stopping VDO vdo
    dmsetup status vdo
    dd if=/dev/zero of=/dev/mapper/vg-lv oflag=direct bs=4096 count=1
vdo: ERROR - dd: failed to open ‘/dev/mapper/vg-lv’: Invalid argument
# ll /dev/mapper
total 0
crw-------. 1 root root 10, 236 Jan  2 03:31 control
lrwxrwxrwx. 1 root root       7 Jan  2 05:42 storageqe_24-root -> ../dm-0
lrwxrwxrwx. 1 root root       7 Jan  2 05:42 storageqe_24-swap -> ../dm-1
-rw-r--r--. 1 root root       0 Jan  3 05:27 vg-lv

Acking...

Comment 3 Joseph Chapman 2018-02-06 16:54:22 UTC
Fixed with change 132391, merged as change 132632.

The bug was caused by a cleanup routine that zeros the first block of a vdo device on remove to prevent accidental re-use. The fix checks to make sure there's still a device present and skips the zeroing step if the device is missing.

Comment 5 Jakub Krysl 2018-02-09 10:53:58 UTC
tested with vdo-6.1.0.146-16, the dd step is not run when the device is missing.

# vgcreate vg /dev/sdb
  Physical volume "/dev/sdb" successfully created.
  Volume group "vg" successfully created
# lvcreate --name lv vg -L 10G
  Logical volume "lv" created.
# vdo create --name vdo --device /dev/mapper/vg-lv
Creating VDO vdo
Starting VDO vdo
Starting compression on VDO vdo
VDO instance 11 volume is ready at /dev/mapper/vdo
# vdo stop --name vdo
Stopping VDO vdo
# vgremove vg -ff
  Logical volume "lv" successfully removed
  Volume group "vg" successfully removed
# vdo remove --name vdo --verbose
Removing VDO vdo
Stopping VDO vdo
    dmsetup status vdo
# ll /dev/mapper/ | grep vdo
#

Comment 8 errata-xmlrpc 2018-04-10 15:49:25 UTC
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2018:0871