Segmentation fault with threaded FFTW FFTW.set_num_threads(n) and julia --threads=k where k, n > 1

[JakobAsslaender]

Hi,
I am getting a segfault error when multithreading both julia and FFTW, but I do not think this is the same bug as reported in #200. Forgive me if I am wrong.

The segfault occurs when writing a script with this content

using FFTW
FFTW.set_num_threads(20)
tmpVec = Array{Complex{Float64},3}(undef, (1024,1024,1024))
FP = plan_fft!(tmpVec; flags = FFTW.MEASURE)

and calling it with julia --threads 20 my_script.jl. The error message is

signal (11): Segmentation fault
in expression starting at .../tmp_debug.jl:9
spawn_apply at .../.julia/artifacts/e95ca94c82899616429924e9fdc7eccda275aa38/lib/libfftw3.so (unknown line)
#2 at ./threadingconstructs.jl:178
unknown function (ip: 0x7e7dc004ba0f)
_jl_invoke at /buildworker/worker/package_linux64/build/src/gf.c:2247 [inlined]
jl_apply_generic at /buildworker/worker/package_linux64/build/src/gf.c:2429
jl_apply at /buildworker/worker/package_linux64/build/src/julia.h:1788 [inlined]
start_task at /buildworker/worker/package_linux64/build/src/task.c:877
Allocations: 1439093 (Pool: 1438431; Big: 662); GC: 2
Segmentation fault

The error does not occur when using a smaller array size (e.g. 512 x 512 x 512), when executing this script in a (multi-threaded) REPL, or when calling julia --threads 1 my_script.jl. Further, I get this error only on our server with large memory:

julia> versioninfo(verbose=true)
Julia Version 1.7.2
Commit bf53498635 (2022-02-06 15:21 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
      "Red Hat Enterprise Linux Server release 7.9 (Maipo)"
  uname: Linux 3.10.0-1160.31.1.el7.x86_64 #1 SMP Wed May 26 20:18:08 UTC 2021 x86_64 x86_64
  CPU: Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz: 
                 speed         user         nice          sys         idle          irq
       #1-40  2400 MHz  124012989 s        151 s    2988670 s  400355468 s          0 s
       
  Memory: 1510.5959396362305 GB (1.20248398046875e6 MB free)
  Uptime: 1.31918749e6 sec
  Load Avg:  76.13  75.18  74.3
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, skylake-avx512)

And not on a server with less memory, but otherwise (AFAIK) equivalent hard- and software:

julia> versioninfo(verbose=true)
Julia Version 1.7.2
Commit bf53498635 (2022-02-06 15:21 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
      "Red Hat Enterprise Linux Server release 7.9 (Maipo)"
  uname: Linux 3.10.0-1160.31.1.el7.x86_64 #1 SMP Wed May 26 20:18:08 UTC 2021 x86_64 x86_64
  CPU: Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz: 
                 speed         user         nice          sys         idle          irq
       #1-40  2400 MHz   21218022 s      22320 s    1268911 s  508883968 s          0 s
       
  Memory: 376.60246658325195 GB (341804.1875 MB free)
  Uptime: 1.32906989e6 sec
  Load Avg:  20.26  11.21  4.94
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, skylake-avx512)

Both machines are using

julia> FFTW.version
v"3.3.10"

(they are using a central julia installation and central config files etc.)

Note that JULIA_COPY_STACKS="yes/no" did not change the behavior, hence I do not believe it is a duplicate of #200.