[patch, libfortran] Fix thead sanitizer issue with libgfortran

[Janne Blomqvist]

On Fri, Sep 29, 2017 at 9:53 PM, Thomas Koenig <tkoenig@netcologne.de> wrote:
> Am 29.09.2017 um 10:03 schrieb Janne Blomqvist:
>
>>
>> 1) I'm confused why fbuf_destroy is modified. The fbuf structure is
>> part of gfc_unit, and should be accessed with the same locking rules
>> as the rest of the gfc_unit components. When closing the unit, I think
>> the same should apply here, no?
>
>
> It is to avoid a data race for
>
> program main
>   use omp_lib
>   !$OMP PARALLEL NUM_THREADS(2)
>   call file_open(OMP_get_thread_num())
>   !$OMP END PARALLEL
> contains
>   recursive subroutine file_open(i)
>   integer :: i
>   integer :: nunit
>   nunit = i + 20
>   write (nunit,*) 'asdf'
>   end subroutine file_open
> end program main
>
> which leads to
>
>   Read of size 4 at 0x7b580000ff30 by main thread (mutexes: write M16):
>     #0 close_unit_1 ../../../trunk/libgfortran/io/unit.c:699
> (libgfortran.so.5+0x000000283ba6)
>     #1 _gfortrani_close_units ../../../trunk/libgfortran/io/unit.c:767
> (libgfortran.so.5+0x000000283f59)
>     #2 cleanup ../../../trunk/libgfortran/runtime/main.c:113
> (libgfortran.so.5+0x00000001fe22)
>     #3 _dl_fini <null> (ld-linux-x86-64.so.2+0x00000000fb62)
>
>   Previous write of size 4 at 0x7b580000ff30 by thread T1 (mutexes: write
> M17):
>     #0 finalize_transfer ../../../trunk/libgfortran/io/transfer.c:3934
> (libgfortran.so.5+0x000000281aa1)
>     #1 _gfortran_st_write_done ../../../trunk/libgfortran/io/transfer.c:4125
> (libgfortran.so.5+0x000000281e35)
>     #2 file_open.3528 <null> (a.out+0x000000400c1b)
>     #3 MAIN__._omp_fn.0 <null> (a.out+0x000000400d27)
>     #4 gomp_thread_start ../../../trunk/libgomp/team.c:120
> (libgomp.so.1+0x00000001756f)
>
> Note that not all problems with implicit close at the end are resolved
> so far, but that is a different problem.

I'm still confused. If gfc_unit->fbuf needs to be protected by holding
gfc_unit->lock when closing, surely the same applies to other
gfc_units fields as well? How if gfc_unit->fbuf special? AFAICS it
isn't..


-- 
Janne Blomqvist