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Subject: Re: [OMPI devel] openib unloaded before last mem dereg
From: Ralph Castain (rhc_at_[hidden])
Date: 2013-01-28 12:48:17


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.

Thanks
Ralph

>
> Steve.
>
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