Re: [Discuss-gnuradio] Segfault in volk_32fc_x2_multiply_32fc_a_avx2_fma

[West, Nathan]

On Mon, Mar 7, 2016 at 10:18 PM, West, Nathan <address@hidden> wrote:

On Mon, Mar 7, 2016 at 2:32 PM, devin kelly <address@hidden> wrote:

Hello,

I've built a flowgraph (grc, python attached) that usually (but not always) produces a segfaults in volk_32fc_x2_multiply_32fc_a_avx2_fma.  The segfault occurs in the FFT filter in correlation estimator block.  I'm not sure if it's the Volk code that's causing the segfault or the GR code calling it or what I'm putting into GR.  I've got a back trace below if that helps. 

Also, at the tag gate in my flowgraph I would usually have a USRP transmitter and a USRP receiver in a before the Correlation Estimate in a separate flowgraph but since I can re-create the segfault in the flowgraph I simplified.

I'm using GR 3.7.9, Volk 1.2.1 and UHD 3.9.2 (though I don't call any UHD code here).

Thanks for any help,

Devin

$ gdb /usr/bin/python core.13408
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-80.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/bin/python2.7...Reading symbols from /usr/bin/python2.7...(no debugging symbols found)...done.
(no debugging symbols found)...done.

[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Core was generated by `python2 ./segfault_test.py'.
Program terminated with signal 11, Segmentation fault.
#0  0x00007f11a4d064c0 in volk_32fc_x2_multiply_32fc_a_avx2_fma () from /local_disk/gr_3.7.9/lib/libvolk.so.1.2.1
Missing separate debuginfos, use: debuginfo-install python-2.7.5-34.el7.x86_64
(gdb) bt
#0  0x00007f11a4d064c0 in volk_32fc_x2_multiply_32fc_a_avx2_fma () at /local_disk/gr_3.7.9/lib/libvolk.so.1.2.1
#1  0x00007f119c1d0006 in gr::filter::kernel::fft_filter_ccc::filter(int, std::complex<float> const*, std::complex<float>*) ()
    at /local_disk/gr_3.7.9/lib64/libgnuradio-filter-3.7.9.so.0.0.0
#2  0x00007f119c4d724f in gr::digital::corr_est_cc_impl::work(int, std::vector<void const*, std::allocator<void const*> >&, std::vector<void*, std::allocator<void*> >&) () at /local_disk/gr_3.7.9/lib64/libgnuradio-digital-3.7.9.so.0.0.0
#3  0x00007f11a52b1f57 in gr::sync_block::general_work(int, std::vector<int, std::allocator<int> >&, std::vector<void const*, std::allocator<void const*> >&, std::vector<void*, std::allocator<void*> >&) () at /local_disk/gr_3.7.9/lib64/libgnuradio-runtime-3.7.9.so.0.0.0
#4  0x00007f11a527a6bd in gr::block_executor::run_one_iteration() () at /local_disk/gr_3.7.9/lib64/libgnuradio-runtime-3.7.9.so.0.0.0
#5  0x00007f11a52baf60 in gr::tpb_thread_body::tpb_thread_body(boost::shared_ptr<gr::block>, int) ()
    at /local_disk/gr_3.7.9/lib64/libgnuradio-runtime-3.7.9.so.0.0.0
#6  0x00007f11a52aebc1 in boost::detail::function::void_function_obj_invoker0<gr::thread::thread_body_wrapper<gr::tpb_container>, void>::invoke(boost::detail::function::function_buffer&) () at /local_disk/gr_3.7.9/lib64/libgnuradio-runtime-3.7.9.so.0.0.0
#7  0x00007f11a5260910 in boost::detail::thread_data<boost::function0<void> >::run() ()
    at /local_disk/gr_3.7.9/lib64/libgnuradio-runtime-3.7.9.so.0.0.0
#8  0x00007f11a40b824a in thread_proxy () at /lib64/libboost_thread-mt.so.1.53.0
#9  0x00007f11bfa38dc5 in start_thread () at /lib64/libpthread.so.0
#10 0x00007f11bf05d28d in clone () at /lib64/libc.so.6

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I couldn't reproduce this on my machine with avx2. Your GRC flowgraph didn't draw anything, so I replaced your FG with random source(0,255) -> const. modulator -> correlation est -> sinks.

I'm wondering if a bad vector length is getting passed in by accident. Can you get the parameters to the VOLK call when it crashes? If you're not familiar with gdb do something like the following:

gdb> f 0

gdb> info variables

Also, I'd like to know what processor you have. I don't think it has anything to do with this bug, but my processor (i7-4700MQ) doesn't generally see much benefit from AVX much less AVX2. What were the times volk_profile gives you for this kernel? (use volk_profile -R 32fc_x2_multiply)