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[Bug 1813045] Re: qemu-ga fsfreeze crashes the kernel
From: |
Thomas Huth |
Subject: |
[Bug 1813045] Re: qemu-ga fsfreeze crashes the kernel |
Date: |
Mon, 09 Aug 2021 09:43:53 -0000 |
See also https://gitlab.com/qemu-project/qemu/-/issues/520
** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #520
https://gitlab.com/qemu-project/qemu/-/issues/520
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https://bugs.launchpad.net/bugs/1813045
Title:
qemu-ga fsfreeze crashes the kernel
Status in QEMU:
Expired
Bug description:
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.
I believe this is the culprit:
/dev/loop0 /tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0
/dev/loop0 /var/tmp ext3 rw,nosuid,noexec,relatime,data=ordered 0 0
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