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Bug 2123648 - Stale devlink device units are not cleaned up while dispatching UDEV change events
Summary: Stale devlink device units are not cleaned up while dispatching UDEV change e...
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 9
Classification: Red Hat
Component: systemd
Version: 9.0
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: systemd-maint
QA Contact: Frantisek Sumsal
URL:
Whiteboard:
Depends On: 2138081
Blocks:
TreeView+ depends on / blocked
 
Reported: 2022-09-02 09:33 UTC by Neil Wilson
Modified: 2023-05-09 10:33 UTC (History)
3 users (show)

Fixed In Version: systemd-252-3.el9
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2023-05-09 08:21:58 UTC
Type: Bug
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Github systemd systemd issues 24518 0 None closed Stale devlink device units are not cleaned up while dispatching UDEV change events 2022-12-07 13:46:59 UTC
Red Hat Issue Tracker RHELPLAN-133121 0 None None None 2022-09-02 09:40:17 UTC
Red Hat Product Errata RHBA-2023:2531 0 None None None 2023-05-09 08:22:25 UTC

Description Neil Wilson 2022-09-02 09:33:47 UTC 
Description of problem:

dangling device units are not unloaded properly, which leads to increased memory usage by subsequent calls to systemctl. 


Version-Release number of selected component (if applicable):

systemd-239-58.el8_6.4
systemd-250-6.el9

How reproducible:


Steps to Reproduce:
1.$ sudo lvcreate -n test-a-1 -L1G test
  Logical volume "test-a-1" created.
2.$ systemctl list-units --all 'dev-disk-by\x2did-dm*'
  UNIT                                                                                                           LOAD   ACTIVE SUB     DESCRIPTION                                                                >
  dev-disk-by\x2did-dm\x2dname\x2dtest\x2dtest\x2d\x2da\x2d\x2d1.device                                          loaded active plugged /dev/disk/by-id/dm-name-test-test--a--1
  dev-disk-by\x2did-dm\x2duuid\x2dLVM\x2dUOSUxz2ZQYd27F1vpz3bAZFukcNK3aQeKgxkfRkc06BhYHctCHcIUhMgQEW1dlIF.device loaded active plugged /dev/disk/by-id/dm-uuid-LVM-UOSUxz2ZQYd27F1vpz3bAZFukcNK3aQeKgxkfRkc06BhYHc>

3.$ sudo lvrename /dev/test/test-a-1 test-a-2
  Renamed "test-a-1" to "test-a-2" in volume group "test"
4.$ systemctl list-units --all 'dev-disk-by\x2did-dm*'
  UNIT                                                                                                           LOAD   ACTIVE SUB     DESCRIPTION                                                                >
  dev-disk-by\x2did-dm\x2dname\x2dtest\x2dtest\x2d\x2da\x2d\x2d1.device                                          loaded active plugged /dev/disk/by-id/dm-name-test-test--a--1
  dev-disk-by\x2did-dm\x2dname\x2dtest\x2dtest\x2d\x2da\x2d\x2d2.device                                          loaded active plugged /dev/disk/by-id/dm-name-test-test--a--2
  dev-disk-by\x2did-dm\x2duuid\x2dLVM\x2dUOSUxz2ZQYd27F1vpz3bAZFukcNK3aQeKgxkfRkc06BhYHctCHcIUhMgQEW1dlIF.device loaded active plugged /dev/disk/by-id/dm-uuid-LVM-UOSUxz2ZQYd27F1vpz3bAZFukcNK3aQeKgxkfRkc06BhYHc>


Actual results:
Currently systemd will create new device units for any new paths appearing in devlinks in a UDEV change event, but will not remove previously-created device units for paths which are no longer present in devlinks. This leaves device units for non-existent paths hanging around until the parent device is removed.

Further in RHEL-8 systemd if a daemon-reload is issued before the parent device unit is removed, the stale devlinks units lose their association with the parent device (through matching syspath) during device enumeration because the paths no longer exist, leaving them hanging around for ever (until rebooting).

Expected results:
Systemd should remove stale devlinks device units while dispatching UDEV "change" events for the parent device (e.g. when renaming an LVM Logical Volume).


Additional info:

Impacts RHEL-8 the most as systemctl enumerates device units when running - causing ever increasing use of memory. 

Similar on RHEL-9 but can be cleared by daemon-reload. 

relevant PRs for the fixes upstream are
https://github.com/systemd/systemd/pull/16968, https://github.com/systemd/systemd/pull/24522
and https://github.com/systemd/systemd-stable/pull/203
Comment 1 David Tardon 2022-09-05 09:13:42 UTC 
I'd expect such device renames and removals should be pretty rare in production, hence the impact of this should be low. Code-wise, the fix hasn't even been merged upstream yet (although it seems to be on the track). I think we could consider this for RHEL-9 (later, after v. 252 with the fix has been released and has got some real-life testing), but backport to RHEL-8 would be non-trivial and IMHO not worth the risk.
Comment 5 errata-xmlrpc 2023-05-09 08:21:58 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 (systemd bug fix and enhancement update), 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/RHBA-2023:2531
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