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https://bugzilla.redhat.com/show_bug.cgi?id=1047659 If a VM dies very early during an attempted connect to the guest agent while the locks are down the domain monitor object will be freed. The object is then accessed later as any failure during guest agent startup isn't considered fatal. In the current upstream version this doesn't lead to a crash as virObjectLock called when entering the monitor in qemuProcessDetectVcpuPIDs checks the pointer before attempting to dereference (lock) it. The NULL pointer is then caught in the monitor helper code. Before the introduction of virObjectLockable - observed on 0.10.2 - the pointer is locked directly via virMutexLock leading to a crash. To avoid this problem we need to differentiate between the guest agent not being present and the VM quitting when the locks were down. The fix reorganizes the code in qemuConnectAgent to add the check and then adds special handling to the callers.
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>