This bug cannot be reproduced again after I update qemu-kvm-1.4.0-3.el7 to qemu-kvm-1.5.0-2.el7. And downgrade the qemu-kvm also will not reproduce it.
the steps like:
1.
# virsh start r7
Domain r7 started
2.
# virsh dompmsuspend r7 --target disk
Domain r7 successfully suspended
3.
# virsh start r7
Domain r7 started
4.
# virsh dompmsuspend r7 --target disk
Domain r7 successfully suspended
5.
# virsh start r7
Domain r7 started
6.
# virsh setmem --live r7 2048000
7.
# virsh dompmsuspend r7 --target disk
error: Domain r7 could not be suspended
error: internal error unable to execute QEMU agent command 'guest-suspend-disk': child process has failed to suspend
the step 7 should hang for this bug, but not.