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Date: Fri, 29 Oct 2021 10:41:57 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: Linux kernel: powerpc: KVM guest can trigger host crash on Power8
To: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>, Michael Ellerman
 <mpe@ellerman.id.au>
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Excerpts from John Paul Adrian Glaubitz's message of October 29, 2021 12:05=
 am:
> Hi Michael!
>=20
> On 10/28/21 13:20, John Paul Adrian Glaubitz wrote:
>> It seems I also can no longer reproduce the issue, even when building th=
e most problematic
>> packages and I think we should consider it fixed for now. I will keep mo=
nitoring the server,
>> of course, and will let you know in case the problem shows again.
>=20
> The host machine is stuck again but I'm not 100% sure what triggered the =
problem:
>=20
> [194817.984249] watchdog: BUG: soft lockup - CPU#80 stuck for 246s! [CPU =
2/KVM:1836]
> [194818.012248] watchdog: BUG: soft lockup - CPU#152 stuck for 246s! [CPU=
 3/KVM:1837]
> [194825.960164] watchdog: BUG: soft lockup - CPU#24 stuck for 246s! [khug=
epaged:318]
> [194841.983991] watchdog: BUG: soft lockup - CPU#80 stuck for 268s! [CPU =
2/KVM:1836]
> [194842.011991] watchdog: BUG: soft lockup - CPU#152 stuck for 268s! [CPU=
 3/KVM:1837]
> [194849.959906] watchdog: BUG: soft lockup - CPU#24 stuck for 269s! [khug=
epaged:318]
> [194865.983733] watchdog: BUG: soft lockup - CPU#80 stuck for 291s! [CPU =
2/KVM:1836]
> [194866.011733] watchdog: BUG: soft lockup - CPU#152 stuck for 291s! [CPU=
 3/KVM:1837]
> [194873.959648] watchdog: BUG: soft lockup - CPU#24 stuck for 291s! [khug=
epaged:318]
> [194889.983475] watchdog: BUG: soft lockup - CPU#80 stuck for 313s! [CPU =
2/KVM:1836]
> [194890.011475] watchdog: BUG: soft lockup - CPU#152 stuck for 313s! [CPU=
 3/KVM:1837]
> [194897.959390] watchdog: BUG: soft lockup - CPU#24 stuck for 313s! [khug=
epaged:318]
> [194913.983218] watchdog: BUG: soft lockup - CPU#80 stuck for 335s! [CPU =
2/KVM:1836]
> [194914.011217] watchdog: BUG: soft lockup - CPU#152 stuck for 335s! [CPU=
 3/KVM:1837]
> [194921.959133] watchdog: BUG: soft lockup - CPU#24 stuck for 336s! [khug=
epaged:318]

Soft lockup should mean it's taking timer interrupts still, just not=20
scheduling. Do you have the hard lockup detector enabled as well? Is
there anything stuck spinning on another CPU?

Do you have the full dmesg / kernel log for this boot?

Could you try a sysrq+w to get a trace of blocked tasks?

Are you able to shut down the guests and exit qemu normally?

Thanks,
Nick