[libvirt] Segfault in qemuDomainDefVcpusPostParse:2480

[Martin Kletzander]

On Sun, Nov 13, 2016 at 11:15:29PM +0530, Nehal J Wani wrote:
>The man page of qemu(2.6.2), states the following:
>
>       -smp
>[cpus=]n[,cores=cores][,threads=threads][,sockets=sockets][,maxcpus=maxcpus]
>           Simulate an SMP system with n CPUs. On the PC target, up to 255
>CPUs are supported. On Sparc32 target, Linux limits the number of usable
>CPUs to 4.  For the PC target, the number of cores per
>           socket, the number of threads per cores and the total number of
>sockets can be specified. Missing values will be computed. *If any on the
>three values is given, the total number of CPUs n can be
>           omitted*. maxcpus specifies the maximum number of hotpluggable
>CPUs.
>
>So, I built the master branch of libvirt and tested the following:
>
>Client:
>
>$ ./run ./tools/virsh domxml-from-native qemu-argv <(echo
>'/usr/bin/qemu-system-x86_64 -enable-kvm -smp cores=2,threads=1,sockets=1')
>error: Disconnected from qemu:///session due to I/O error
>error: Cannot recv data: Connection reset by peer
>
>Server:
>
>$ ./run gdb ./daemon/libvirtd
>GNU gdb (GDB) Fedora 7.11.1-86.fc24
>...
>Starting program: /home/wani/libvirt/daemon/.libs/lt-libvirtd
>[Thread debugging using libthread_db enabled]
>...
>[Thread 0x7fffc462c700 (LWP 16850) exited]
>...
>Thread 4 "lt-libvirtd" received signal SIGSEGV, Segmentation fault.
>[Switching to Thread 0x7fffe4cf1700 (LWP 16836)]
>qemuDomainDefVcpusPostParse (def=0x7fffb8000ec0) at qemu/qemu_domain.c:2480
>2480    if (!vcpu->online) {
>
>
>qemuDomainDefVcpusPostParse() calls vcpu = virDomainDefGetVcpu(def, 0),
>which returns NULL.
>
>I'd be happy to send a patch, but I am not sure what the right solution is.
>
>- Should not specifying n to -smp allowed?

I don't understand that ^^.

>- Should -cpus=n also be parsed in qemuParseCommandLineSmp()?
>

But the parsing code should be fixed.  Looks like the value could be
just computed.  But domxml-to-native is not very used I believe.

>Cheers!
>Nehal J Wani

>--
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>libvir-list at redhat.com
>https://www.redhat.com/mailman/listinfo/libvir-list
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