Comment 9 for bug 1872945

Test via https://people.ubuntu.com/~wgrant/riscv64/

Talking with Wgrant there also was an atomic fix that he has on his build.
The upstream version of it is [1] and some other bits in that series.
That is in since 4.0.

Another testcase (unsure if it is the same root cause, but easier to test for now).
Start via:
$ qemu-system-riscv64 -machine virt -m 8192 -smp 4 -kernel bbl-vmlinuz-5.4.0-23-generic -initrd initrd.img-5.4.0-23-generic -append "console=ttyS0 rw noquiet root=/dev/vda1" -device virtio-blk-device,drive=vda -drive file=focal-riscv64-20200411.qcow2,id=vda -device virtio-net-device,netdev=eth0 -netdev user,id=eth0,hostfwd=tcp::22222-:22

Check SSH which will hang:
$ ssh -v root@localhost -p 22222
...
debug1: SSH2_MSG_SERVICE_ACCEPT received

Wgrant reports that this also worked with his patched 3.1 but fails with 4.2 as in Ubuntu.

I tried that with:
- qemu 4.2 Ubuntu archive - failing
- git master (5.0-rc) - working
- git 4.0 - working
- git 4.1 - working
- git 4.2 - failing

So it is not in the Ubuntu Delta but between 5.1 and 4.2.
I think I can bisect from here - once we know what it is we can cross check if it is the same root case that also caused ckings failure.

[1]: https://git.qemu.org/?p=qemu.git;a=commit;h=c13b169f1a3dd158d6c75727cdc388f95988db39