semantic: 0.217
device: 0.172
other: 0.158
files: 0.082
graphic: 0.062
PID: 0.059
performance: 0.043
socket: 0.037
vnc: 0.035
debug: 0.033
network: 0.031
permissions: 0.029
boot: 0.026
KVM: 0.015
debug: 0.440
other: 0.113
network: 0.098
files: 0.058
performance: 0.058
socket: 0.056
PID: 0.037
semantic: 0.035
device: 0.023
permissions: 0.018
vnc: 0.017
KVM: 0.017
boot: 0.016
graphic: 0.014

qemu-ga fsfreeze crashes the kernel

Hello,

Still required your attention, duplicate from:
https://bugs.launchpad.net/bugs/1807073
https://bugs.launchpad.net/bugs/1813045

We use mainly Cloudlinux, Debian and Centos.
We experienced many crashes on our qemu instances based on Cloudlinux during a snapshot.
The issue is not related to CloudLinux directly, but to Qemu agent, which does not freeze the file system(s) correctly. What is actually happening:

When VM backup is invoked, Qemu agent freezes the file systems, so no single change will be made during the backup. But Qemu agent does not respect the loop* devices in freezing order (we have checked its sources), which leads to the next situation:
1) freeze loopback fs
              ---> send async reqs to loopback thread
2) freeze main fs
3) loopback thread wakes up and trying to write data to the main fs, which is still frozen, and this finally leads to the hung task and kernel crash.

Moreover, a lot of Proxmox users are complaining about the issue as well:
https://forum.proxmox.com/threads/error-vm-100-qmp-command-guest-fsfreeze-thaw-failed-got-timeout.68082/
https://forum.proxmox.com/threads/problem-with-fsfreeze-freeze-and-qemu-guest-agent.65707/

We are currently in progress of retiring this bug tracker here... could you please open a new ticket on gitlab instead:

 https://gitlab.com/qemu-project/qemu/-/issues

Thanks and sorry for the inconvenience.

https://gitlab.com/qemu-project/qemu/-/issues/520
... thanks!