Processes launched during the NIC load is high may hang up.

[Hatt Maru]

1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu
❯ lsb_release -rd
Description: Ubuntu 21.04
Release: 21.04

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center
❯ LANG=C apt-cache policy linux-raspi
linux-raspi:
  Installed: 5.11.0.1009.7
  Candidate: 5.11.0.1009.7
  Version table:
 *** 5.11.0.1009.7 500
        500 http://ports.ubuntu.com/ubuntu-ports hirsute-updates/main arm64 Packages
        500 http://ports.ubuntu.com/ubuntu-ports hirsute-security/main arm64 Packages
        100 /var/lib/dpkg/status
     5.11.0.1007.5 500
        500 http://ports.ubuntu.com/ubuntu-ports hirsute/main arm64 Packages

3) What you expected to happen
Processes launched during the NIC load is high will exit normally.

4) What happened instead
I'm using hirsute on Raspberry Pi 4 model B(4GB RAM).
Some processes launched during the NIC load is high might not exit.

What "NIC load is high" means:
- I have configured crontab to run Ookla's speedtest-cli which generates heavy network traffic every 15 minites.
- During speedtest-cli, Softirq becomes higher.
- SoC(BCM2711) built-in NIC(driver is bcmgenet)

What "may not exit" means:
- Some processes launched during speedtest-cli is running will not exit. It remains with consuming CPU 100% and not accept any signals including SIGKILL.
- Those processes can't be attached by gdb or strace. Trying to do so, gdb and strace will freeze.

I could't terminate the processes in any way. But the system could be rebooted by "sudo reboot" command.

I configured RFS/RPS to distribute Softirq among CPU cores. It was quite effective, but did not prevent the problem completely.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Brian Murray (brian-murray)]

The Hirsute Hippo has reached End of Life, so this bug will not be fixed for that release.