[Bug 2143080] [NEW] [Ubuntu 26.04] Running iperf3 client for longer duration causes OOM on guest

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Problem Description:
Brought up Ubuntu 26.04 guest with a single bridge interface, ran iperf3 in server mode on the host and started iperf3 client on the guest, connecting to the server on the host via the bridge IP, with 8000 sec test time on client. At some point in the first hour or two, OOM is observed on the guest, with sudden memory usage spike.

Guest bridge xml snippet:
<interface type='bridge'>
<mac address='52:54:00:08:0d:f8'/>
<source bridge='virbr0'/>
<model type='rtl8139'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
</interface>

System Information:
Linux ltcden6-lp4 6.18.0-8-generic #8-Ubuntu SMP PREEMPT_DYNAMIC Wed Dec 17 15:52:06 UTC 2025 ppc64le GNU/Linux
PRETTY_NAME="Ubuntu Resolute Raccoon (development branch)"
NAME="Ubuntu"
VERSION_ID="26.04"
VERSION="26.04 (Resolute Raccoon)"
VERSION_CODENAME=resolute
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=resolute
LOGO=ubuntu-logo

Steps to reproduce:
1. Start guest domain console with virsh start <domain name> --console
2. On a separate tab, start the iperf3 server on the host machine with the following command to use port 6969 (any port that is available is okay to use)
iperf3 -s -p 6969
3. Check the ip of virbr0 (or the bridge network in use by the guest)
ip addr
keep a note of the ip of virbr0 (or the bridge network in use), lets assume 192.168.122.1 at the moment
4. In the guest console tab, run the iperf3 client in background, attach the server IP as the IP address of the bridge noted above, with the port you started the iperf3 server at, specify the time as 8000 seconds, and monitor dmesg logs
- nohup iperf3 -c 192.198.122.1 -p 6969 -t 8000 > iperf3client.log &
- dmesg -w
5. Monitor the dmesg logs for OOM errors.

==
Here's a log from a previous run where we see OOM logs dumped on the console:

[ 5] 1339.00-1340.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1340.00-1341.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1341.00-1342.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[63842.605982] Out of memory: Killed process 1291 (systemd) total-vm:30016kB, anon-rss:4096kB, file-rss:6144kB, shmem-rss:0kB, UID:0 pgtables:32kB oom_score_adj:100
[63842.616019] Out of memory: Killed process 1293 ((sd-pam)) total-vm:33728kB, anon-rss:6208kB, file-rss:2048kB, shmem-rss:0kB, UID:0 pgtables:28kB oom_score_adj:100
[ 5] 1342.00-1343.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1343.00-1344.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1344.00-1345.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1345.00-1346.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1346.00-1347.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1347.00-1348.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1348.00-1349.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1349.00-1350.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1350.00-1351.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1351.00-1352.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1352.00-1353.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1353.00-1354.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1354.00-1355.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1355.00-1356.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1356.00-1357.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[63858.021746] Out of memory: Killed process 968 (named) total-vm:217088kB, anon-rss:77760kB, file-rss:6144kB, shmem-rss:0kB, UID:106 pgtables:42kB oom_score_adj:0
[ 5] 1357.00-1358.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1358.00-1359.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1359.00-1360.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes
[ 5] 1360.00-1361.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes

Some insight from recent tests:

1. This issue is not reproducible when the iperf3 guest and host are both run on the LPAR itself.
2. Issue is also not reproducible with virtio driver (All the previous tests have been with RTL8139 driver).

** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
Status: New


** Tags: architecture-ppc64le bugnameltc-217559 severity-high targetmilestone-inin---
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[Ubuntu 26.04] Running iperf3 client for longer duration causes OOM on guest
https://bugs.launchpad.net/bugs/2143080
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