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Signaling the condition before vm->def->id is reset to -1 is dangerous:
in case a waiting thread wakes up, it does not see anything interesting
(the domain is still marked as running) and just enters virDomainObjWait
where it waits forever because the condition will never be signalled
again.
Originally it was impossible to get into such situation because the vm
object was locked all the time between signaling the condition and
resetting vm->def->id, but after commit 860a999802 released in 6.8.0,
qemuDomainObjStopWorker called in qemuProcessStop between
virDomainObjBroadcast and setting vm->def->id to -1 unlocks the vm
object giving other threads a chance to wake up and possibly hang.
In real world, this can be easily reproduced by killing, destroying, or
just shutting down (from the guest OS) a domain while it is being
migrated somewhere else. The migration job would never finish.
So let's make sure we delay signaling the domain condition to the point
when a woken up thread can detect the domain is not active anymore.
https://bugzilla.redhat.com/show_bug.cgi?id=1949869
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
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==============================
Libvirt API for virtualization
==============================
Libvirt provides a portable, long term stable C API for managing the
virtualization technologies provided by many operating systems. It
includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware
vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER
Hypervisor.
For some of these hypervisors, it provides a stateful management
daemon which runs on the virtualization host allowing access to the
API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other
languages including Python, Perl, PHP, Go, Java, OCaml, as well as
mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the
website:
https://libvirt.org
License
=======
The libvirt C API is distributed under the terms of GNU Lesser General
Public License, version 2.1 (or later). Some parts of the code that are
not part of the C library may have the more restrictive GNU General
Public License, version 2.0 (or later). See the files ``COPYING.LESSER``
and ``COPYING`` for full license terms & conditions.
Installation
============
Instructions on building and installing libvirt can be found on the website:
https://libvirt.org/compiling.html
Contributing
============
The libvirt project welcomes contributions in many ways. For most components
the best way to contribute is to send patches to the primary development
mailing list. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
Contact
=======
The libvirt project has two primary mailing lists:
* libvirt-users@redhat.com (**for user discussions**)
* libvir-list@redhat.com (**for development only**)
Further details on contacting the project are available on the website:
https://libvirt.org/contact.html