Re: [patch, libfortran] Fix thead sanitizer issue with libgfortran

[Thomas Koenig <tkoenig@netcologne.de>]

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.

> 2) I think the mutex init stuff can remain in insert_unit, just the
> locking needs to move out and below freeing unit_lock like you have
> done.

I can change that one easily.

Any other comments?

Regards

	Thomas