Issue report: Snapshot-create-as block while the vm's process is killed out.

[Peter Krempa]

On Mon, Aug 16, 2021 at 11:04:12 +0800, 13520781732 at 189.cn wrote:
> 
> Hello, 
> 
> I have meet one issues while using snapshot-create-as with external file.
> 
> Centos 8, 
> Libivirt 7.0.0
> Qemu: 5.2.0
> 
> While making one snapshot with  memory and disk extaernal file,  and killing the process of the vm qemu same time mostly,  the snapshot-create-as command blocked.
> So it will failed to  start the vm again for "cannot acquire state change lock (held by monitor=remoteDispatchDomainSnapshotCreateXML)".

[...]

> 
> 
> The call work flow one is: 
> qemuSnapshotCreateActiveExternal -> qemuSaveImageCreate -> qemuMigrationSrcToFile -> qemuMigrationSrcWaitForCompletion -> virDomainObjWait 
> 
> The others is similar :
>  qemuSnapshotCreateXML 　－＞　．．．
> 
> 
> It may be resume after the restart libvirtd.service.
> 
> Is it correct that the stat change lock should be unlocked while the vm is terminal or shutdown and how to fix it?

The function handling the shutdown of the monitor is supposed to wake up
all waiting threads, which should prevent such a problem.

In this case the log attached is not enough to see what's really
happening, so please attach a full debug log and ideally report the
issue in our gitlab issue tracker:

https://gitlab.com/libvirt/libvirt/-/issues/new

Guidance on how to setup logging for debugging can be found at:

https://libvirt.org/kbase/debuglogs.html#less-verbose-logging-for-qemu-vms