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[Qemu-devel] Livelock with qemu 2.5.0


From: Brian Candler
Subject: [Qemu-devel] Livelock with qemu 2.5.0
Date: Fri, 2 Dec 2016 14:19:45 +0000
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0) Gecko/20100101 Thunderbird/45.5.1

I am running a VM under qemu 2.5.0/Ubuntu 16.04. The guest VM is also Ubuntu 16.04, with ZFS and LXD, and I am hitting it hard with I/O, concurrently building multiple LXD containers. Previously it was serialized to build one container at a time, and it was fine.

With the concurrent builds I got to a point where the VM livelocked:

- CPU utilisation on the host is 100%:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM TIME+ COMMAND
20321 libvirt+ 20 0 18.864g 0.014t 23032 S 100.3 45.7 603:33.30 qemu-system-x86

(host has 32GB of RAM, plenty of headroom there)

- VM does not respond to ping

- I can connect to VM's VNC console, and it shows the login prompt, but keystrokes are ignored

I attached gdb and took backtraces (attached)

I imagine I could have hit a problem either with qemu, or with the guest kernel itself. So next I'm going to try to replicate this with qemu 2.7.0. But I thought I'd post the backtraces here first to see if anyone has any comments/thoughts about what's going on.

Thanks,

Brian.

P.S. I'm not subscribed to qemu-devel so please CC me directly.

Attachment: qemu-2.5.0-livelock.txt
Description: Text document


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