Re: test_x86_64_hotplug_cpu.py times out frequently in CI

[Thomas Huth <thuth@redhat.com>]

On 06/01/2025 17.49, Peter Maydell wrote:
> On Mon, 6 Jan 2025 at 16:45, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>>
>> Hi Thomas,
>> test_x86_64_hotplug_cpu.py times out frequently in CI runs. Here is an example:
>> https://gitlab.com/qemu-project/qemu/-/jobs/8777540230#L1151
>>
>> The detailed test logs are here:
>> https://gitlab.com/qemu-project/qemu/-/jobs/8777540230/artifacts/browse/build/tests/functional/x86_64/test_x86_64_hotplug_cpu.HotPlugCPU.test_hotplug/
>>
>> I looked at this failure with Dan and Peter on IRC. It was pointed out
>> that the final command assumes that device_del takes effect
>> immediately. The console log shows that the CPU was still visible to
>> the guest when the final command executed.
>>
>> Could be a bug in QEMU, the test, or both?
>>
>> 2025-01-06 15:45:29,308: :/#
>> 2025-01-06 15:45:29,313: cd /sys/devices/system/cpu/cpu0
>> 2025-01-06 15:45:29,315: :/sys/devices/system/cpu/cpu0#
>> 2025-01-06 15:45:29,320: cd /sys/devices/system/cpu/cpu1
>> 2025-01-06 15:45:29,322: sh: cd: /sys/devices/system/cpu/cpu1: No such
>> file or directory
>> 2025-01-06 15:45:29,325:
>> 2025-01-06 15:45:29,330: :/sys/devices/system/cpu/cpu0# [    7.337146]
>> CPU1 has been hot-added
>> 2025-01-06 15:45:29,330:
>> 2025-01-06 15:45:29,335: cd /sys/devices/system/cpu/cpu1
>> 2025-01-06 15:45:29,337: :/sys/devices/system/cpu/cpu1#
>> 2025-01-06 15:45:29,342: cd /sys/devices/system/cpu/cpu1
> 
> Though the fact that there is no final shell prompt after
> the last 'cd' command is perhaps evidence against this being
> a simple race where the guest execution of the "cd" command
> beat the guest handling of the hot-unplug event.

Yes, sounds like a race ... I'll try to come up with a patch to fix it.

  Thomas