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Subject: Re: [OMPI devel] openib unloaded before last mem dereg
From: Steve Wise (swise_at_[hidden])
Date: 2013-01-28 14:25:40


On 1/28/2013 12:48 PM, Ralph Castain wrote:
> Hmmm...afraid I cannot replicate this using the current state of the 1.6 branch (which is the 1.6.4rcN) on the only IB-based cluster I can access.
>
> Can you try it with a 1.6.4 tarball and see if you still see the problem? Could be someone already fixed it.

I still hit it on 1.6.4rc2.

Note iWARP != IB so you may not have this issue on IB systems for
various reasons. Did you use the same mpirun line? Namely using this:

  --mca btl_openib_ipaddr_include "192.168.170.0/24"

(adjusted to your network config).

Because if I don't use ipaddr_include, then I don't see this issue on my
setup.

Also, did you see these logged:

Right after starting the job:

--------------------------------------------------------------------------
No OpenFabrics connection schemes reported that they were able to be
used on a specific port. As such, the openib BTL (OpenFabrics
support) will be disabled for this port.

   Local host: hpc-hn1.ogc.int
   Local device: cxgb4_0
   Local port: 2
   CPCs attempted: oob, xoob, rdmacm
--------------------------------------------------------------------------
...

At the end of the job:

[hpc-hn1.ogc.int:07850] 5 more processes have sent help message
help-mpi-btl-openib-cpc-base.txt / no cpcs for port

I think these are benign, but prolly indicate a bug: the mpirun is
restricting the job to use port 1 only, so the CPCs shouldn't be
attempting port 2...

Steve.

>
> On Jan 28, 2013, at 10:03 AM, Steve Wise <swise_at_[hidden]> wrote:
>
>> On 1/28/2013 11:48 AM, Ralph Castain wrote:
>>> On Jan 28, 2013, at 9:12 AM, Steve Wise <swise_at_[hidden]> wrote:
>>>
>>>> On 1/25/2013 12:19 PM, Steve Wise wrote:
>>>>> Hello,
>>>>>
>>>>> I'm tracking an issue I see in openmpi-1.6.3. Running this command on my chelsio iwarp/rdma setup causes a seg fault every time:
>>>>>
>>>>> /usr/mpi/gcc/openmpi-1.6.3-dbg/bin/mpirun --np 2 --host hpc-hn1,hpc-cn2 --mca btl openib,sm,self --mca btl_openib_ipaddr_include "192.168.170.0/24" /usr/mpi/gcc/openmpi-1.6.3/tests/IMB-3.2/IMB-MPI1 pingpong
>>>>>
>>>>> The segfault is during finalization, and I've debugged this to the point were I see a call to dereg_mem() after the openib blt is unloaded via dlclose(). dereg_mem() dereferences a function pointer to call the btl-specific dereg function, in this case it is openib_dereg_mr(). However, since that btl has already been unloaded, the deref causes a seg fault. Happens every time with the above mpi job.
>>>>>
>>>>> Now, I tried this same experiment with openmpi-1.7rc6 and I don't see the seg fault, and I don't see a call to dereg_mem() after the openib btl is unloaded. That's all well good. :) But I'd like to get this fix pushed into 1.6 since that is the current stable release.
>>>>>
>>>>> Question: Can someone point me to the fix in 1.7?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Steve.
>>>> It appears that in ompi_mpi_finalize(), mca_pml_base_close() is called which unloads the openib btl. Then further down in ompi_mpi_finalize(), mca_mpool_base_close() is called which ends up calling dereg_mem() which seg faults trying to call into the unloaded openib btl.
>>>>
>>> That definitely sounds like a bug
>>>
>>>> Anybody have thoughts? Anybody care? :)
>>> I care! It needs to be fixed - I'll take a look. Probably something that forgot to be cmr'd.
>> Great! If you want me to try out a fix or gather more debug, just hollar.
>>
>> Thanks,
>>
>> Steve.
>>