Hi All,
I've been investigating a hang/freeze of some of our VM's when running a
snapshot on them.
The cause seems to be that the fsFreeze call before the snapshot gets
locked forever due to the use of a loop device.
There are multiple reports about this, like [1] or [2].
Also there is a quite easy way to simulate it, see [3].
Now this seems to happen when you do a ioctl FIFREEZE on a mount point
that is backed by a loop device.
For ex:
/dev/loop0 3.9G 508K 3.7G 1% /tmp
And loop0 is:
/dev/loop0: [2052]:25308501 (/usr/tmpDSK)
Now if you lock the disk/partition that has /usr, and then you want to
lock /tmp, it will hang forever (or until you thaw the /usr disk).
You would expect that the call returns -EBUSY like the others, but that
is not the case.
Is this something we want to solve? Or does somebody have better idea's
on how to resolve this?
The Qemu issue is already a long standing issue, which I want to get
resolved :)
Thanks
Jean-Louis
[1]: https://gitlab.com/qemu-project/qemu/-/issues/592
[2]:
https://forum.proxmox.com/threads/snapshot-backup-not-working-guest-agent-fs-freeze-gets-timeout.99887/
[3]: https://gitlab.com/qemu-project/qemu/-/issues/520#note_1879103020
