Cannot change MemoryKSM in systemd units

[Pierre-Olivier Vallès]

[Impact]

Units with MemoryKSM=yes setting will fail to start with an "Invalid argument" error. This makes the setting unusable on Noble.

[Test Plan]

On Noble, start a systemd service with MemoryKSM=yes:

$ systemd-run -u test-memory-ksm.service --wait -p MemoryKSM=yes /usr/bin/true

On an affected system, this will fail immediately. Inspecting the journal will show why, e.g.:

$ journalctl -u test-memory-ksm.service
Oct 17 10:37:20 six (sleep)[1494131]: test-memory-ksm.service: Failed to set KSM: Invalid argument
Oct 17 10:37:20 six systemd[1]: Started test-memory-ksm.service - /usr/bin/sleep infinity.
Oct 17 10:37:20 six systemd[1]: test-memory-ksm.service: Main process exited, code=exited, status=245/KSM
Oct 17 10:37:20 six systemd[1]: test-memory-ksm.service: Failed with result 'exit-code'.

On a patched system, the unit should start/exit normally.

[Where problems could occur]

This patch simply adds missing arguments to the prctl call for PR_SET_MEMORY_MERGE. Problems would be isolated to the MemoryKSM= setting.

[Other information]

The patch is from upstream: https://github.com/systemd/systemd/commit/9bb89a55a235a3c64ec099bb86296d7fd1bb3302

[Original Description]

In one of my working unit (service), I try to toggle the MemoryKSM boolean setting.

Using any of:

MemoryKSM=yes
MemoryKSM=on
MemoryKSM=true
MemoryKSM=1

Results in:

Sep 19 16:16:56 systemd[1]: Started XXX.service - XXX service.
Sep 19 16:16:56 (e_server)[4487]: XXX.service: Failed to set KSM: Invalid argument
Sep 19 16:16:56 systemd[1]: XXX.service: Main process exited, code=exited, status=245/KSM
Sep 19 16:16:56 systemd[1]: XXX.service: Failed with result 'exit-code'.

The following lines allow the service to start:

MemoryKSM="yes"
MemoryKSM="on"
MemoryKSM="true"
MemoryKSM="1"

but still, MemoryKSM stays off:

# systemctl show XXX.service | grep MemoryKSM
MemoryKSM=no

KSM is activated in my running kernel:
# cat /boot/config-$(uname -r) | grep KSM
CONFIG_KSM=y

Using prctl (libc6 2.39-0ubuntu8.3) to toggle KSM inside a running process also works. I can read and set the memory_merge switch.

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: systemd 255.4-1ubuntu8.4
ProcVersionSignature: Ubuntu 6.8.0-45.45-generic 6.8.12
Uname: Linux 6.8.0-45-generic x86_64
ApportVersion: 2.28.1-0ubuntu3.1
Architecture: amd64
CasperMD5CheckResult: unknown
CloudArchitecture: x86_64
CloudBuildName: server
CloudID: openstack
CloudName: openstack
CloudPlatform: openstack
CloudSerial: 20240612
CloudSubPlatform: metadata (http://169.254.169.254)
Date: Thu Sep 19 16:06:51 2024
Lsusb:
 Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd QEMU Tablet
 Bus 001 Device 003: ID 0627:0001 Adomax Technology Co., Ltd QEMU Tablet
Lsusb-t:
 /: Bus 001.Port 001: Dev 001, Class=root_hub, Driver=uhci_hcd/2p, 12M
     |__ Port 001: Dev 002, If 0, Class=Human Interface Device, Driver=usbhid, 12M
     |__ Port 002: Dev 003, If 0, Class=Human Interface Device, Driver=usbhid, 12M
MachineType: OpenStack Foundation OpenStack Nova
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-6.8.0-45-generic root=UUID=1c5e2fdc-a746-403d-9fc0-71af31bc9c19 ro console=tty1 console=ttyS0
SourcePackage: systemd
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 02/06/2015
dmi.bios.release: 0.0
dmi.bios.vendor: EFI Development Kit II / OVMF
dmi.bios.version: 0.0.0
dmi.chassis.type: 1
dmi.chassis.vendor: QEMU
dmi.chassis.version: pc-q35-4.2
dmi.modalias: dmi:bvnEFIDevelopmentKitII/OVMF:bvr0.0.0:bd02/06/2015:br0.0:svnOpenStackFoundation:pnOpenStackNova:pvr26.2.3:cvnQEMU:ct1:cvrpc-q35-4.2:sku:
dmi.product.family: Virtual Machine
dmi.product.name: OpenStack Nova
dmi.product.version: 26.2.3
dmi.sys.vendor: OpenStack Foundation

[Nick Rosbrook (enr0n)]

Thanks for reporting this. I can reproduce as well. It appears this was fixed upstream in https://github.com/systemd/systemd/pull/31683.

It should already be fixed in Oraculr, but we will backport this to Noble.

[Pierre-Olivier Vallès (povalles)]

Thank you very much for the quick reply and pointing to the PR.

We are launching hundreds of similar processes on this server ; we migrated to Noble especially for this new feature (MemoryKSM).

Any idea when the backport will occur? We're eager to try it out.

[Nick Rosbrook (enr0n)]

I have uploaded the proposed fix to noble-proposed. It needs to be reviewed by the SRU team, then tested, and eventually released to noble-updates. This process overall can take a couple of weeks depending on how busy the SRU team is.

[Timo Aaltonen (tjaalton)]

Hello Pierre-Olivier, or anyone else affected,

Accepted systemd into noble-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/systemd/255.4-1ubuntu8.5 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-noble to verification-done-noble. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-noble. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Nick Rosbrook (enr0n)]

I have verified the fix using systemd 255.4-1ubuntu8.5 from noble-proposed:

$ cat > /etc/apt/sources.list.d/proposed.sources << EOF
> Types: deb
URIs: http://archive.ubuntu.com/ubuntu/
Suites: noble-proposed
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
> EOF
$ apt update
Hit:1 http://us.archive.ubuntu.com/ubuntu noble InRelease
Get:2 http://us.archive.ubuntu.com/ubuntu noble-updates InRelease [126 kB]
Get:3 http://security.ubuntu.com/ubuntu noble-security InRelease [126 kB]
Get:4 http://archive.ubuntu.com/ubuntu noble-proposed InRelease [265 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu noble-backports InRelease [126 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu noble-updates/main amd64 Packages [663 kB]
Hit:7 https://ppa.launchpadcontent.net/enr0n/systemd/ubuntu noble InRelease
Get:8 http://us.archive.ubuntu.com/ubuntu noble-updates/main Translation-en [156 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu noble-updates/main amd64 Components [120 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu noble-updates/main Icons (48x48) [32.4 kB]
Get:11 http://us.archive.ubuntu.com/ubuntu noble-updates/main Icons (64x64) [47.0 kB]
Get:12 http://us.archive.ubuntu.com/ubuntu noble-updates/main amd64 c-n-f Metadata [10.4 kB]
Get:13 http://us.archive.ubuntu.com/ubuntu noble-updates/restricted amd64 Packages [473 kB]
Get:14 http://us.archive.ubuntu.com/ubuntu noble-updates/restricted Translation-en [91.2 kB]
Get:15 http://us.archive.ubuntu.com/ubuntu noble-updates/restricted amd64 Components [212 B]
Get:16 http://us.archive.ubuntu.com/ubuntu noble-updates/restricted amd64 c-n-f Metadata [424 B]
Get:17 http://us.archive.ubuntu.com/ubuntu noble-updates/universe amd64 Packages [718 kB]
Get:18 http://us.archive.ubuntu.com/ubuntu noble-updates/universe Translation-en [213 kB]
Get:19 http://us.archive.ubuntu.com/ubuntu noble-updates/universe amd64 Components [310 kB]
Get:20 http://us.archive.ubuntu.com/ubuntu noble-updates/universe Icons (48x48) [170 kB]
Get:21 http://us.archive.ubuntu.com/ubuntu noble-updates/universe Icons (64x64) [269 kB]
Get:22 http://us.archive.ubuntu.com/ubuntu noble-updates/universe amd64 c-n-f Metadata [19.9 kB]
Get:23 http://us.archive.ubuntu.com/ubuntu noble-updates/multiverse amd64 Packages [15.0 kB]
Get:24 http://us.archive.ubuntu.com/ubuntu noble-updates/multiverse amd64 Components [940 B]
Get:25 http://us.archive.ubuntu.com/ubuntu noble-updates/multiverse amd64 c-n-f Metadata [552 B]
Get:26 http://us.archive.ubuntu.com/ubuntu noble-backports/main amd64 Components [208 B]
Get:27 http://us.archive.ubuntu.com/ubuntu noble-backports/restricted amd64 Components [212 B]
Get:28 http://u...

[Pierre-Olivier Vallès (povalles)]

I have also verified the fix using systemd 255.4-1ubuntu8.5 from noble-proposed.

I was able to launch the transient unit with MemoryKSM=yes (this step used to fail without the fix) and now systemctl reports:

# systemctl show povalles-j | grep -i memoryksm
MemoryKSM=yes

Thank you! Now I can move on and test KSM itself :-)

[Ubuntu SRU Bot (ubuntu-sru-bot)]

All autopkgtests for the newly accepted systemd (255.4-1ubuntu8.5) for noble have finished running.
The following regressions have been reported in tests triggered by the package:

linux-nvidia/6.8.0-1020.22 (arm64)
linux-oem-6.8/unknown (amd64)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/noble/update_excuses.html#systemd

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

[Launchpad Janitor (janitor)]

This bug was fixed in the package systemd - 255.4-1ubuntu8.5

---------------
systemd (255.4-1ubuntu8.5) noble; urgency=medium

  [ Chengen Du ]
  * udev: Handle PTP device symlink properly on udev action 'change'
    (LP: #2077779)

  [ Nick Rosbrook ]
  * core/exec-invoke: Fix missing arguments for PR_SET_MEMORY_MERGE call
    (LP: #2081192)

 -- Nick Rosbrook <email address hidden> Thu, 17 Oct 2024 13:15:16 -0400

[Andreas Hasenack (ahasenack)]

The verification of the Stable Release Update for systemd has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.