I have meet one issues while using snapshot-create-as with external file.

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 log is as bellow:

2021-08-12 10:27:38.373+0000: 4344: error : qemuDomainAgentAvailable:8125 : Guest agent is not responding: QEMU guest agent is not connected

2021-08-12 10:27:38.573+0000: 4340: error : qemuDomainAgentAvailable:8125 : Guest agent is not responding: QEMU guest agent is not connected

2021-08-12 10:27:38.757+0000: 128211: error : qemuDomainAgentAvailable:8125 : Guest agent is not responding: QEMU guest agent is not connected

2021-08-12 10:27:39.397+0000: 4341: error : qemuDomainAgentAvailable:8125 : Guest agent is not responding: QEMU guest agent is not connected

2021-08-12 10:27:39.887+0000: 4309: error : virNetSocketReadWire:1817 : End of file while reading data: Input/output error

2021-08-12 10:27:53.735+0000: 4340: error : qemuDomainAgentAvailable:8125 : Guest agent is not responding: QEMU guest agent is not connected

2021-08-12 10:27:54.822+0000: 4344: error : qemuDomainAgentAvailable:8125 : Guest agent is not responding: QEMU guest agent is not connected

2021-08-12 10:27:55.230+0000: 4340: error : qemuDomainAgentAvailable:8125 : Guest agent is not responding: QEMU guest agent is not connected

2021-08-12 10:46:40.994+0000: 4344: warning : qemuDomainObjTaint:6187 : Domain id=95 name='vm_6_135' uuid=b2812e01-331a-4e65-912b-73be5ace2271 is tainted: high-privileges

2021-08-12 10:48:05.785+0000: 4309: error : virNetSocketReadWire:1817 : End of file while reading data: Input/output error

2021-08-12 10:49:50.440+0000: 1643666: error : qemuMonitorIO:583 : internal error: End of file from qemu monitor

2021-08-12 10:50:13.809+0000: 4341: warning : qemuDomainObjTaint:6187 : Domain id=96 name='vm_6_135' uuid=b2812e01-331a-4e65-912b-73be5ace2271 is tainted: high-privileges

2021-08-12 10:51:21.587+0000: 1646757: error : qemuMonitorIO:583 : internal error: End of file from qemu monitor

2021-08-12 10:52:28.421+0000: 4342: warning : qemuDomainObjBeginJobInternal:953 : Cannot start job (none, none, start) for domain vm_6_135; current job is (none, none, snapshot) owned by (0 <null>, 0 <null>, 4340 remoteDispatchDomainSnapshotCreateXML (flags=0x280)) for (0s, 0s, 67s)

2021-08-12 10:52:28.421+0000: 4342: error : qemuDomainObjBeginJobInternal:975 : Timed out during operation: cannot acquire state change lock (held by monitor=remoteDispatchDomainSnapshotCreateXML)

2021-08-12 10:53:10.522+0000: 4342: warning : qemuDomainObjBeginJobInternal:953 : Cannot start job (none, none, start) for domain vm_6_135; current job is (none, none, snapshot) owned by (0 <null>, 0 <null>, 4340 remoteDispatchDomainSnapshotCreateXML (flags=0x280)) for (0s, 0s, 109s)

2021-08-12 10:53:10.522+0000: 4342: error : qemuDomainObjBeginJobInternal:975 : Timed out during operation: cannot acquire state change lock (held by monitor=remoteDispatchDomainSnapshotCreateXML)

2021-08-12 10:53:17.821+0000: 128211: warning : qemuDomainObjBeginJobInternal:953 : Cannot start job (none, none, start) for domain vm_6_135; current job is (none, none, snapshot) owned by (0 <null>, 0 <null>, 4340 remoteDispatchDomainSnapshotCreateXML (flags=0x280)) for (0s, 0s, 117s)

2021-08-12 10:53:17.821+0000: 128211: error : qemuDomainObjBeginJobInternal:975 : Timed out during operation: cannot acquire state change lock (held by monitor=remoteDispatchDomainSnapshotCreateXML)

... ...

2021-08-13 05:49:41.240+0000: 4342: warning : qemuDomainObjBeginJobInternal:953 : Cannot start job (none, none, start) for domain vm_6_135; current job is (none, none, snapshot) owned by (0 <null>, 0 <null>, 4340 remoteDispatchDomainSnapshotCreateXML (flags=0x280)) for (0s, 0s, 68300s)

Gdb attach the proces of the libvirt, found there are two suspicious threads, stack as below:

#0 0x00007f8f91a492fc in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0

#1 0x00007f8f9574ed7a in virCondWait () from /lib64/libvirt.so.0

#2 0x00007f8f95784ef5 in virDomainObjWait () from /lib64/libvirt.so.0

#3 0x00007f8f422eb26d in qemuMigrationSrcWaitForCompletion () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#4 0x00007f8f422ee5d3 in qemuMigrationSrcToFile () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#5 0x00007f8f42331caa in qemuSaveImageCreate () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#6 0x00007f8f42336ac0 in qemuSnapshotCreateXML () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#7 0x00007f8f422b6ac1 in qemuDomainSnapshotCreateXML () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#8 0x00007f8f9591f604 in virDomainSnapshotCreateXML () from /lib64/libvirt.so.0

#9 0x0000562390841b81 in remoteDispatchDomainSnapshotCreateXMLHelper ()

#10 0x00007f8f9580e807 in virNetServerProgramDispatch () from /lib64/libvirt.so.0

#11 0x00007f8f95813b26 in virNetServerHandleJob () from /lib64/libvirt.so.0

#12 0x00007f8f9574f85f in virThreadPoolWorker () from /lib64/libvirt.so.0

#13 0x00007f8f9574eecb in virThreadHelper () from /lib64/libvirt.so.0

#14 0x00007f8f91a4314a in start_thread () from /lib64/libpthread.so.0

#15 0x00007f8f941f1f23 in clone () from /lib64/libc.so.6

(gdb) bt

#0 0x00007f8f91a492fc in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0

#1 0x00007f8f9574ed7a in virCondWait () from /lib64/libvirt.so.0

#2 0x00007f8f95784ef5 in virDomainObjWait () from /lib64/libvirt.so.0

#3 0x00007f8f42257ac8 in qemuBlockStorageSourceCreateGeneric () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#4 0x00007f8f4225b88d in qemuBlockStorageSourceCreate () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#5 0x00007f8f423346ee in qemuSnapshotDiskPrepareOne () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so

#6 0x00007f8f423353f8 in qemuSnapshotCreateXML () from /usr/lib64/libvirt/connection-driver/libvirt_driver_qemu.so