On Mon, Feb 06, 2012 at 03:59:19PM +0100, Michal Privoznik wrote:
> On 06.02.2012 10:08, Guannan Ren wrote:
> >
> >
> > Hi,
> >
> > The Makefile.am in python forget to add probes.o if WITH_DTRACE
> > but after I added it and tried to connect, using
> > libvirt.open("qemu:///system")
> > in python , it reported: "segment fault"
> > I tried to figure out, but failed. If anyone can help this, thanks.
> >
> > The following is the backtrace:
> >
> > #0 0x0000003c62a810a4 in free () from /lib64/libc.so.6
> > #1 0x00007ffff1836f29 in virFree (ptrptr=0x6a6a28) at
> > util/memory.c:310
> > #2 0x00007ffff1849692 in virResetError (err=0x6a6a20) at
> > util/virterror.c:387
> > #3 0x00007ffff13e2761 in do_open (name=0x7ffff7ed6444
> > "qemu:///system", auth=0x0, flags=0) at libvirt.c:1093
> > #4 0x00007ffff13e4d44 in virConnectOpen (name=0x7ffff7ed6444
> > "qemu:///system") at libvirt.c:1350
> > #5 0x00007ffff1824879 in libvirt_virConnectOpen (self=<optimized
> > out>, args=<optimized out>) at libvirt.c:3637
> > #6 0x0000003c652dffbb in PyEval_EvalFrameEx () from
> > /usr/lib64/libpython2.7.so.1.0
> > #7 0x0000003c652e0580 in PyEval_EvalFrameEx () from
> > /usr/lib64/libpython2.7.so.1.0
> > #8 0x0000003c652e15a5 in PyEval_EvalCodeEx () from
> > /usr/lib64/libpython2.7.so.1.0
> > #9 0x0000003c652e16d2 in PyEval_EvalCode () from
> > /usr/lib64/libpython2.7.so.1.0
> > #10 0x0000003c652fb9ec in ?? () from /usr/lib64/libpython2.7.so.1.0
> > #11 0x0000003c652fc7f0 in PyRun_FileExFlags () from
> > /usr/lib64/libpython2.7.so.1.0
> > #12 0x0000003c652fd26f in PyRun_SimpleFileExFlags () from
> > /usr/lib64/libpython2.7.so.1.0
> > #13 0x0000003c6530e745 in Py_Main () from
> > /usr/lib64/libpython2.7.so.1.0
> > #14 0x0000003c62a2169d in __libc_start_main () from /lib64/libc.so.6
> > #15 0x0000000000400651 in _start ()
> >
> > Guannan Ren
> >
>
>
> Running git bisect showed it was caused by
> c700613b8d463212d142c97108b7a2352e23e559. However, I think it only
> exposed the design problem we are facing here.
>
> IMHO problem is when an application tries to call virConnectOpen() (or
> virConnectOpenAuth()) from two concurrent threads. This is what will happen:
>
> 1st thread:
> call virConnectOpen();
> global variable @initialized == zero; thus virInitialize() is called,
> error object is set up (via virErrorInitialize()) which is thread local
> variable. However, @initialized is set to 1 in the first place.
>
> 2nd thread:
> call virConnectOpen() as well;
> @initialized is already set, therefore no thread local variable is set
> and any error report will fail.
>
> Even if I am right, I am not sure how to fix this.
In a mulithreaded application, you should be calling virInitialize()
explicitly, instead of relying on lazy init. IMHO, the python module
should simply be calling virInitialize at time of import.
Regards,
Daniel
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