[libvirt] libvirtd segfault

[Michal Privoznik]

On 28.12.2012 20:23, Scott Sullivan wrote:
<snip/>
> I have just now received another SIGSEGV, with your patch applied.
> 
> Here's the info from the GDB session:
> 
> Detaching after fork from child process 11266.
> 2012-12-28 18:56:53.261+0000: 29943: error : qemuMonitorIO:614 :
> internal error End of file from monitor
> 
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7fffec0cd700 (LWP 29955)]
> qemuDomainObjBeginJobInternal (driver=0x7fffe4013520,
> driver_locked=true, obj=0x7fff7801fc80, job=QEMU_JOB_DESTROY,
> asyncJob=QEMU_ASYNC_JOB_NONE) at qemu/qemu_domain.c:780
> 780         priv->jobs_queued++;
> (gdb) bt
> #0  qemuDomainObjBeginJobInternal (driver=0x7fffe4013520, driver_locked=true, obj=0x7fff7801fc80, job=QEMU_JOB_DESTROY, asyncJob=QEMU_ASYNC_JOB_NONE) at qemu/qemu_domain.c:780
> #1  0x00007fffea599f46 in qemuDomainDestroyFlags (dom=<value optimized out>, flags=<value optimized out>) at qemu/qemu_driver.c:2189
> #2  0x00007ffff7a83587 in virDomainDestroy (domain=0x7fffe414a510) at libvirt.c:2215
> #3  0x00000000004296e2 in remoteDispatchDomainDestroy (server=<value optimized out>, client=<value optimized out>, msg=<value optimized out>, rerr=0x7fffec0ccbc0, args=<value optimized out>, ret=<value optimized out>) at remote_dispatch.h:1277
> #4  remoteDispatchDomainDestroyHelper (server=<value optimized out>, client=<value optimized out>, msg=<value optimized out>, rerr=0x7fffec0ccbc0, args=<value optimized out>, ret=<value optimized out>) at remote_dispatch.h:1255
> #5  0x00007ffff7ad0d02 in virNetServerProgramDispatchCall (prog=0x6814d0, server=0x678df0, client=0x693a80, msg=0x6986d0) at rpc/virnetserverprogram.c:431
> #6  virNetServerProgramDispatch (prog=0x6814d0, server=0x678df0, client=0x693a80, msg=0x6986d0) at rpc/virnetserverprogram.c:304
> #7  0x00007ffff7aceaa6 in virNetServerProcessMsg (srv=<value optimized out>, client=0x693a80, prog=<value optimized out>, msg=0x6986d0) at rpc/virnetserver.c:173
> #8  0x00007ffff7acf5e3 in virNetServerHandleJob (jobOpaque=<value optimized out>, opaque=0x678df0) at rpc/virnetserver.c:194
> #9  0x00007ffff79e8fdc in virThreadPoolWorker (opaque=<value optimized out>) at util/threadpool.c:144
> #10 0x00007ffff79e88c9 in virThreadHelper (data=<value optimized out>) at util/threads-pthread.c:161
> #11 0x000000300a2077f1 in start_thread () from /lib64/libpthread.so.0
> #12 0x0000003009ae570d in clone () from /lib64/libc.so.6
> (gdb)

This means, even though we successfully incremented reference counter on
virDomainObjPtr object, somebody free()d it anyway (well, the
privateData at least). Looks like a locking/concurrent access issue to
me then. Unfortunately, I don't have any suggestions yet, as the domain
object is supposed to be locked when entering the
qemuDomainObjBeginJobInternal() function so it shouldn't get free()d
meanwhile.

Michal