[libvirt] Segfault in qemuDomainDefVcpusPostParse:2480
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? - Should -cpus=n also be parsed in qemuParseCommandLineSmp()? Cheers! Nehal J Wani
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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On Mon, Nov 14, 2016 at 09:50:02 +0100, Martin Kletzander wrote:
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')
This command line is parsed as having 0 online cpus and 0 maximum cpus in libvirt as we did not update the code for a while.
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.
This happens as the code happily sets vcpus to 0. The post parse code expects at least 1 vcpu.
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.
There are three issues with the code: 1: if the total calculated vcpu count is 0 libvirt does not reject it - this causes the crash 2: qemu now supports the cpus= parameter which libvirt does not parse 3: qemu accepts topology as a valid way how to specify maximum cpu count I'll post patches in a while.
participants (3)
-
Martin Kletzander -
Nehal J Wani -
Peter Krempa