Bug#737675: openblas: openmp change deadlocks python-scipy

[Sébastien Villemot]

[re-adding the bug in CC]

Le mercredi 12 février 2014 à 18:19 +0100, Julian Taylor a écrit :
> On Wed, Feb 12, 2014 at 6:09 PM, Sébastien Villemot
> <sebastien at debian.org> wrote:
>         Control: tags -1 + upstream
>         Control: forwarded -1
>         https://github.com/xianyi/OpenBLAS/issues/294
>         
>         Le mardi 04 février 2014 à 22:58 +0100, Julian Taylor a
>         écrit :
>         > On 04.02.2014 22:52, Sébastien Villemot wrote:
>         > > Le mardi 04 février 2014 à 22:42 +0100, Julian Taylor a
>         écrit :
>         > >
>         > >> it will deadlock eating all cpu in gomp at the end.
>         > >> This is the typical failure pattern caused by forks
>         combined with gnu
>         > >> openmp (see
>         https://github.com/xianyi/OpenBLAS/issues/294)
>         > >>
>         > >> But the weird part is this testsuite does not fork at
>         all, so it might
>         > >> be a different issue.
>         > >> It did not occur when openblas was still using pthreads.
>         
>         
>         My understanding of the issue is that Python violates the
>         POSIX API when
>         forking, and that GCC does not handle that case as well as
>         some
>         proprietary compilers. A proposal to change the behavior of
>         GCC has been
>         posted at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60035
>         
>         Until GCC is modified (if it is ever), the OpenBLAS maintainer
>         is trying
>         to implement a solution at its level (see the github issue at
>         the top of
>         this message).
>         
>         Julian: does that seem an accurate summary of the situation to
>         you?
> 
> 
> no, too my knowledge python forks correctly, fork without execve is
> allowed.
> gnu openmp simply does not support this type of forking.
> R seems to fork in the same way see
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=684344#35
> 
> 
> The weird thing in the scipy test case is that no forking is done.
> 
> This could be an bug in openmp itself or scipy corrupting some memory
> as I don't see openblas doing anything weird when using openmp.

So we don't even know at this stage if the present bug is a bug in GCC,
scipy or openmp. It would help if you could clarify this.

-- 
 .''`.    Sébastien Villemot
: :' :    Debian Developer
`. `'     http://www.dynare.org/sebastien
  `-      GPG Key: 4096R/381A7594

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