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Re: [libvirt] segment fault from libvirtmod



On 06.02.2012 15:59, 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.
> 
> Michal
> 

Sorry for mystification. Here's the debug output which shows what's wrong:

http://fpaste.org/6pBs/

However, I am not sure what is causing it.


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