/usr/lib/qubes/cleanup-dispvms hangs

[DemiMarie]

How to file a helpful issue

Qubes OS release

R4.2

Brief summary

/usr/lib/qubes/cleanup-dispvms hangs

Steps to reproduce

Not sure. This happened once for me.

Expected behavior

It doesn’t hang, or at least does not hang the boot process.

Actual behavior

Freezes and hangs the boot process.

[marmarek]

Which dom0 kernel? If 6.5, it might be #8575

[DemiMarie]

Which dom0 kernel? If 6.5, it might be #8575

uname -r gives 6.1.57-1.qubes.fc37.x86_64.

[rustybird]

Did you by any chance boot with preempt=full when it happened?

[DemiMarie]

Did you by any chance boot with preempt=full when it happened?

Yes, why do you ask?

[rustybird]

Just a hunch. No smoking gun yet :)

I've had what might have been a similar kind of hang like @marmarek's in #8575 a week or two ago, on shutting down a VM while lots of I/O was going on elsewhere. Unfortunately I didn't trigger a sysrq "Show Blocked State" back then to compare. His does involve dm-crypt. My system (which is on the newest kernel-latest 6.5.x) uses Btrfs not LVM; maybe LVM is just a bit more likely, if even that, to trigger some bug in the device-mapper or a lower layer of the storage stack?

And so I've been wondering if the scheduling change in kernel-latest v6.5.5+ could make this hypothetical bug more likely to cause an actual hang. Although that's probably because the recent LWN article series on reworking the kernel's preemption code (part 1, part 2) has primed me to see it as a potential source of trouble.

[DemiMarie]

@rustybird I don’t think this was a kernel deadlock. systemctl restart qubesd.service solved the problem.

[rustybird]

So qubes-core.service was hanging during boot before login, and running systemctl restart qubesd.service (how?) unwedged it?

[DemiMarie]

Duplicate of #8754 which has more information as to the actual cause.

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