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FS#55231 - [linux] OpenBSD running under QEMU freezes

Attached to Project: Arch Linux
Opened by viq (viq) - Monday, 21 August 2017, 22:12 GMT
Last edited by Evangelos Foutras (foutrelis) - Thursday, 19 April 2018, 20:08 GMT
Task Type Bug Report
Category Packages: Core
Status Assigned
Assigned To Tobias Powalowski (tpowa)
Evangelos Foutras (foutrelis)
Jan Alexander Steffens (heftig)
Levente Polyak (anthraxx)
Architecture All
Severity High
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 0%
Votes 0
Private No


After upgrading linux to 4.12.8-2 from 4.12.8-1 OpenBSD-current in qemu driven by libvirt freezes before or shortly after login is reached. I see the same behaviour with linux-hardened 4.12.8-2, I did not try with previous versions of it.

I was seeing random freezes previously, but they were random - now, the box usually doesn't manage to fully boot before the freeze.

Additional info:
* package versions:
$ pacmatic -Q | egrep '(^linux |qemu|virt)'
libvirt 3.6.0-1
libvirt-python2 3.6.0-1
linux 4.12.8-1
qemu-headless 2.9.0-3

* config and/or log files etc.
not sure what to paste here. Those are just normal OpenBSD-current amd64 machines. Some are bridged, some aren't, some have 2 CPUs, some 1, I gave them 1 or 2 GB RAM, all have LVM-backed disks. No logs are generated, VM simply stops responding to anything and qemu process uses 100% of one core.

Steps to reproduce:
Upgrade kernel to 4.12.8-2, try to run OpenBSD in qemu (I did not try with other systems, as that's what I have)
This task depends upon

Comment by viq (viq) - Tuesday, 22 August 2017, 07:32 GMT
Sorry, I remembered I did not try the non-bridged VM with 4.12.8-2, since that VM requires others for networking and those were not working.
Comment by revel (revel) - Monday, 04 September 2017, 05:12 GMT
It looks like linux-4.12.8-1 is built with GCC: (GNU) 7.1.1 20170630, whereas linux-4.12.8-2 with GCC: (GNU) 7.2.0 (which apparently is still in testing)
Comment by Doug Newgard (Scimmia) - Monday, 04 September 2017, 05:31 GMT
Which has nothing to do with this ticket. Don't hijack.
Comment by Finke Lamein (Quattro) - Tuesday, 05 September 2017, 13:41 GMT looks like it might be related? even though on Xen it doesn't boot at all?
Comment by Frank Denis (jedisct1) - Wednesday, 13 September 2017, 11:41 GMT
Just a "me too".

Same symptoms, also running OpenBSD-current on KVM.

Had to go back to the -lts kernel as a workaround.
Comment by Frank Denis (jedisct1) - Wednesday, 13 September 2017, 11:54 GMT
"Which has nothing to do with this ticket". Actually, it may have something to do with it.

The changes between linux-4.12.8-1 and linux-4.12.8-2 are minor and are unlikely to be related to the KVM/Xen issues.

linux-4.13* kernels exhibit the same symptoms.

What they have in common is indeed the compiler version. gcc 7.2 introduced some new optimizations that may have triggered something unexpected in the compiled kernels.

Comment by viq (viq) - Monday, 25 September 2017, 21:54 GMT
I've moved to linux-hardened, and now had the same thing happen on update from 4.13.1.b-1 to 4.13.3.a-1
Comment by Evangelos Foutras (foutrelis) - Monday, 16 April 2018, 23:13 GMT
Is this still an issue with current QEMU and kernel?
Comment by viq (viq) - Thursday, 19 April 2018, 20:03 GMT
Yes, very much so. OpenBSD guests regularly hang, but while it is happening "every so often" on 4.15.17-1-hardened or 4.15.15-1-hardened, on 4.15.16-1-hardened a machine was failing to get to login prompt before hanging.

$ pacman -Q linux-hardened qemu-headless
linux-hardened 4.15.17.a-1
qemu-headless 2.11.1-2