Re: BUG: soft lockup - CPU#0 stuck for 26s! with nested KVM on 5.19.x

František Šumšal
2022-09-07T15:12:05Z

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On 9/7/22 17:08, Sean Christopherson wrote:
> On Wed, Sep 07, 2022, František Šumšal wrote:
>> Hello!
>>
>> In our Arch Linux part of the upstream systemd CI I recently noticed an
>> uptrend in CPU soft lockups when running one of our tests. This test runs
>> several systemd-nspawn containers in succession and sometimes the underlying
>> VM locks up due to a CPU soft lockup
>
> By "underlying VM", do you mean L1 or L2? Where
>
> L0 == Bare Metal
> L1 == Arch Linux (KVM, 5.19.5-arch1-1/5.19.7-arch1-1)
> L2 == Arch Linux (nested KVM or QEMU TCG, 5.19.5-arch1-1/5.19.7-arch1-1)

I mean L2.

>
>> (just to clarify, the topology is: CentOS Stream 8 (baremetal,
>> 4.18.0-305.3.1.el8) -> Arch Linux (KVM, 5.19.5-arch1-1/5.19.7-arch1-1) ->
>> Arch Linux (nested KVM or QEMU TCG, happens with both,
>> 5.19.5-arch1-1/5.19.7-arch1-1) -> nspawn containers).
>
> Since this repros with TCG, that rules out nested KVM as the cuplrit.\

Ah, that's a good point, thanks.

>
>> I did some further testing, and it reproduces even when the baremetal is my
>> local Fedora 36 machine (5.17.12-300.fc36.x86_64).
>>
>> Unfortunately, I can't provide a simple and reliable reproducer, as I can
>> reproduce it only with that particular test and not reliably (sometimes it's
>> the first iteration, sometimes it takes an hour or more to reproduce).
>> However, I'd be more than glad to collect more information from one such
>> machine, if possible.
>
> ...
>
>> Also, in one instance, the machine died with:
>
> Probably unrelated, but same question as above: which layer does "the machine"
> refer to?

Same as in the previous case - it's the L2.