julia> FFTW.version # is that the linked library? How to change that?
v"3.3.9"

julia> versioninfo()
Julia Version 1.6.1
Commit 6aaedecc44 (2021-04-23 05:59 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: AMD Ryzen 5 5600X 6-Core Processor
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, generic)
Environment:
  JULIA_NUM_THREADS = 12
  JULIA_COPY_STACKS = yes

➜  ~ export JULIA_COPY_STACKS="yes"
➜  ~ julia --threads=2             
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.6.1 (2021-04-23)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> begin
           using FFTW
           FFTW.set_num_threads(12)
           x = randn((400, 400, 13))
           fft(x);
       end;

signal (11): Segmentation fault
in expression starting at REPL[1]:1
spawn_apply at /home/fxw/.julia/artifacts/81791030d1dcd08bf0c67b3e8224cb573d0f5a0a/lib/libfftw3.so (unknown line)
#2 at ./threadingconstructs.jl:169
unknown function (ip: 0x7f10e857072f)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2237 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2419
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1703 [inlined]
start_task at /buildworker/worker/package_linux64/build/src/task.c:839
jl_init_root_task at /buildworker/worker/package_linux64/build/src/task.c:1288
_julia_init at /buildworker/worker/package_linux64/build/src/init.c:800
repl_entrypoint at /buildworker/worker/package_linux64/build/src/jlapi.c:702
main at julia (unknown line)

signal (11): Segmentation fault
in expression starting at REPL[1]:1
spawn_apply at /home/fxw/.julia/artifacts/81791030d1dcd08bf0c67b3e8224cb573d0f5a0a/lib/libfftw3.so (unknown line)
#2 at ./threadingconstructs.jl:169
unknown function (ip: 0x7f10e857072f)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2237 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2419
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1703 [inlined]
start_task at /buildworker/worker/package_linux64/build/src/task.c:839
jl_init_root_task at /buildworker/worker/package_linux64/build/src/task.c:1288
jl_threadfun at /buildworker/worker/package_linux64/build/src/partr.c:264
start_thread at /lib/x86_64-linux-gnu/libpthread.so.0 (unknown line)
clone at /lib/x86_64-linux-gnu/libc.so.6 (unknown line)
Allocations: 2005171 (Pool: 2004448; Big: 723); GC: 4
[1]    5639 segmentation fault (core dumped)  julia --threads=2
➜  ~ export JULIA_COPY_STACKS="no" 
➜  ~ julia --threads=2            
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.6.1 (2021-04-23)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> begin
           using FFTW
           FFTW.set_num_threads(12)
           x = randn((400, 400, 13))
           fft(x);
       end;