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Message #03719
[Bug 2078347] Proposed package upload rejected
An upload of s390-tools to noble-proposed has been rejected from the
upload queue for the following reason: "As requested by uploader".
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https://bugs.launchpad.net/bugs/2078347
Title:
[UBUNTU 24.04] Udev/rules: Missing rules causes newly added CPUs to
stay offline
Status in Ubuntu on IBM z Systems:
In Progress
Status in s390-tools package in Ubuntu:
Fix Released
Status in s390-tools-signed package in Ubuntu:
Fix Released
Status in s390-tools source package in Noble:
In Progress
Status in s390-tools-signed source package in Noble:
In Progress
Status in s390-tools source package in Plucky:
In Progress
Status in s390-tools-signed source package in Plucky:
In Progress
Status in s390-tools source package in Questing:
Fix Released
Status in s390-tools-signed source package in Questing:
Fix Released
Bug description:
SRU Justification:
[ Impact ]
* Newly (online) CPUs that are hotpluggable and that are added to a
live system, are not immediately used and stay offline.
* They only become online after a reboot.
But the reason to add CPUs is usually an immediate need for more
capacity, so that a reboot with downtime is not wanted.
* This can be addressed by a udev rule in /etc/udev/rules.d/ like:
SUBSYSTEM=="cpu", ACTION=="add", CONST{arch}=="s390*", \
ATTR{configure}=="1", TEST=="online", ATTR{online}!="1", ATTR{online}="1"
that automatically hotplugs any (new) CPUs added to the system to
configured state.
[ Fix ]
* 8dc06d14d769 ("udev: Introduce a rule to set newly hotplugged CPUs online")
https://github.com/ibm-s390-linux/s390-tools/commit/\
8dc06d14d76940b3059cd6063fc7d8e7f0150271
[ Test Plan ]
* Adding CPU to a system in online and configured state is possible
in LPARs, z/VM guests or KVM virtual machines.
It's easiest to test this with the help of KVM.
* Setup an Ubuntu Server 24.04 LPAR with KVM vrt-stack.
* Define a KVM guest with hotpluggable and non-hotpluggable CPUs
whereas the amount of used (current) CPUs is lower than the
overall amount (let's say 6 out of 8):
virsh dumpxml vm
<domain type='kvm' id='106'>
...
<vcpu placement='static' current='6'>8</vcpu>
<vcpus>
<vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
<vcpu id='1' enabled='yes' hotpluggable='no' order='2'/>
<vcpu id='2' enabled='yes' hotpluggable='yes' order='3'/>
<vcpu id='3' enabled='yes' hotpluggable='yes' order='4'/>
<vcpu id='4' enabled='yes' hotpluggable='yes' order='5'/>
<vcpu id='5' enabled='yes' hotpluggable='yes' order='6'/>
<vcpu id='6' enabled='no' hotpluggable='yes'/>
<vcpu id='7' enabled='no' hotpluggable='yes'/>
</vcpus>
* Now attempt to add CPUs to the guest in a live "running" state.
$ virsh setvcpus vm 8 --live
* The KVM guest XML is updated :
...
<vcpu placement='static'>8</vcpu>
<vcpus>
<vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
<vcpu id='1' enabled='yes' hotpluggable='no' order='2'/>
<vcpu id='2' enabled='yes' hotpluggable='yes' order='3'/>
<vcpu id='3' enabled='yes' hotpluggable='yes' order='4'/>
<vcpu id='4' enabled='yes' hotpluggable='yes' order='5'/>
<vcpu id='5' enabled='yes' hotpluggable='yes' order='6'/>
<vcpu id='6' enabled='yes' hotpluggable='yes' order='7'/>
<vcpu id='7' enabled='yes' hotpluggable='yes' order='8'/>
</vcpus>
* But the CPUs inside of the guest still stay offline:
$ lscpu -e
CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS
0 0 0 0 0 0 0:0:0 yes yes horizontal 0
1 0 0 0 1 1 1:1:1 yes yes horizontal 1
2 0 0 0 2 2 2:2:2 yes yes horizontal 2
3 0 0 0 3 3 3:3:3 yes yes horizontal 3
4 0 0 0 4 4 4:4:4 yes yes horizontal 4
5 0 0 0 5 5 5:5:5 yes yes horizontal 5
6 - - - - - - no yes horizontal 6
7 - - - - - - no yes horizontal 7
* The desired result, achieved with the help of the new udev rule
is like this:
$ lscpu -e
CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS
0 0 0 0 0 0 0:0:0 yes yes horizontal 0
1 0 0 0 1 1 1:1:1 yes yes horizontal 1
2 0 0 0 2 2 2:2:2 yes yes horizontal 2
3 0 0 0 3 3 3:3:3 yes yes horizontal 3
4 0 0 0 4 4 4:4:4 yes yes horizontal 4
5 0 0 0 5 5 5:5:5 yes yes horizontal 5
6 0 0 0 6 6 6:6:6 yes yes horizontal 6
7 0 0 0 7 7 7:7:7 yes yes horizontal 7
* Without the udev rule, this can only be achieved with a reboot.
But it's not desired, since in cases where immediately new CPU
capacity is needed, a downtime (caused by a reboot) is counterproductive.
[ Where problems could occur ]
* This is only a configuration change and not a code change.
However, things could still go wrong:
- No or not desired functionality in case the udev rules
is installed in a wrong folder.
- The udev rule itself could be wrong.
- wrong subsystem would lead to listen to a wrong event
- wrong action would lead to wrong behavior
- wrong architecture would run the rule not on s390x
(as architecture constant "s390*" is used here,
which covers s390x and s390, but Ubuntu supports
s390x (64-bit) only, but since it's upstream like this
it should be kept)
- wrong attribute would lead to wrong behavior, action
or status.
* Since the architecture constant is s390(x), this affects
IBM Z and LinuxONE only, and has no impact on other architectures.
[ Other Info ]
* Since this is the same for all Linux distros,
this udev rule was added to the s390-tools in general.
(The s390-tools package already ships udev rules for other purposes.)
* It's already included in questing, with the updated s390-tools
version 2.38.0 (as part of LP: #2115416).
__________
---Problem Description----------------------------------------------------------------------------------
Adding a configured CPU to a system (LPAR, ZVM or KVM) leaves that CPU configured but hotplugged off.
# lscpu -e
CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS
0 0 0 0 0 0 0:0:0 yes yes horizontal 0
1 0 0 0 1 1 1:1:1 yes yes horizontal 1
2 0 0 0 2 2 2:2:2 yes yes horizontal 2
3 0 0 0 3 3 3:3:3 yes yes horizontal 3
4 0 0 0 4 4 4:4:4 yes yes horizontal 4
5 0 0 0 5 5 5:5:5 yes yes horizontal 5
6 - - - - - - no yes horizontal 6
7 - - - - - - no yes horizontal 7
---Debugger---
A debugger is not configured
Machine Type = z/VM, LPAR
---uname output---
6.8.0-41-generic #41-Ubuntu SMP Fri Aug 2 19:51:49 UTC 2024 s390x s390x s390x GNU/Linux
---Steps to Reproduce---
Easiest way to reproduce is using a KVM guest to add new CPUs.
1. Before adding CPUs:
$ virsh dumpxml vm
<domain type='kvm' id='106'>
...
<vcpu placement='static' current='6'>8</vcpu>
<vcpus>
<vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
<vcpu id='1' enabled='yes' hotpluggable='no' order='2'/>
<vcpu id='2' enabled='yes' hotpluggable='yes' order='3'/>
<vcpu id='3' enabled='yes' hotpluggable='yes' order='4'/>
<vcpu id='4' enabled='yes' hotpluggable='yes' order='5'/>
<vcpu id='5' enabled='yes' hotpluggable='yes' order='6'/>
<vcpu id='6' enabled='no' hotpluggable='yes'/>
<vcpu id='7' enabled='no' hotpluggable='yes'/>
2. Attempt to add CPUs to the guest in a "running" state.
$ virsh setvcpus vm 8 --live
3. The guest XML is updated :
...
<vcpu placement='static'>8</vcpu>
<vcpus>
<vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
<vcpu id='1' enabled='yes' hotpluggable='no' order='2'/>
<vcpu id='2' enabled='yes' hotpluggable='yes' order='3'/>
<vcpu id='3' enabled='yes' hotpluggable='yes' order='4'/>
<vcpu id='4' enabled='yes' hotpluggable='yes' order='5'/>
<vcpu id='5' enabled='yes' hotpluggable='yes' order='6'/>
<vcpu id='6' enabled='yes' hotpluggable='yes' order='7'/>
<vcpu id='7' enabled='yes' hotpluggable='yes' order='8'/>
</vcpus>
4. But inside the guest, the CPUs are in offline state:
$ lscpu -e
CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS
0 0 0 0 0 0 0:0:0 yes yes horizontal 0
1 0 0 0 1 1 1:1:1 yes yes horizontal 1
2 0 0 0 2 2 2:2:2 yes yes horizontal 2
3 0 0 0 3 3 3:3:3 yes yes horizontal 3
4 0 0 0 4 4 4:4:4 yes yes horizontal 4
5 0 0 0 5 5 5:5:5 yes yes horizontal 5
6 - - - - - - no yes horizontal 6
7 - - - - - - no yes horizontal 7
5. Post rebooting the guest, the CPUs are online:
$ virsh reboot vm
Inside the guest:
$ lscpu -e
CPU NODE DRAWER BOOK SOCKET CORE L1d:L1i:L2 ONLINE CONFIGURED POLARIZATION ADDRESS
0 0 0 0 0 0 0:0:0 yes yes horizontal 0
1 0 0 0 1 1 1:1:1 yes yes horizontal 1
2 0 0 0 2 2 2:2:2 yes yes horizontal 2
3 0 0 0 3 3 3:3:3 yes yes horizontal 3
4 0 0 0 4 4 4:4:4 yes yes horizontal 4
5 0 0 0 5 5 5:5:5 yes yes horizontal 5
6 0 0 0 6 6 6:6:6 yes yes horizontal 6
7 0 0 0 7 7 7:7:7 yes yes horizontal 7
The CPUs should be online after adding them to the system.
Other distros already have a udev rule to circumvent this under;
/etc/udev/rules.d/
The rule does a check if a newly added CPUs are configured but not
online, then hotplugs it to make it online. If CPUs are NOT configured
then they should stay offline.
Contact Information = mete.durlu@xxxxxxx
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