[Bug sanitizer/55561] TSAN: Fortran/OMP yields false positives

["dvyukov at google dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55561

--- Comment #19 from Dmitry Vyukov <dvyukov at google dot com> 2012-12-29 09:38:13 UTC ---
On Wed, Dec 26, 2012 at 12:23 AM, Joost.VandeVondele at mat dot
ethz.ch <gcc-bugzilla@gcc.gnu.org> wrote:
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55561
>
> --- Comment #16 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> 2012-12-25 20:23:07 UTC ---
> many things appear to work fine, but seemingly parallel do loops with a dynamic
> schedule generate warnings in libgomp. I also seem to observe that they are not
> strictly deterministic, sometimes these warnings happen, sometimes not.
>
> Testcase:
>
> !$OMP PARALLEL PRIVATE(j)
>
> j=OMP_GET_THREAD_NUM()
>
> ! no warnings without the dynamic schedule
> !$OMP DO SCHEDULE(DYNAMIC,2)
> DO i=1,10
> ENDDO
>
> !$OMP END PARALLEL
> END
>
> Result:
>
> vjoost@nanosim-s01.ethz.ch:/data/vjoost/clean/cp2k/cp2k/src> ./a.out
> vjoost@nanosim-s01.ethz.ch:/data/vjoost/clean/cp2k/cp2k/src> ./a.out
> vjoost@nanosim-s01.ethz.ch:/data/vjoost/clean/cp2k/cp2k/src> ./a.out
> vjoost@nanosim-s01.ethz.ch:/data/vjoost/clean/cp2k/cp2k/src> ./a.out
> ==================
> WARNING: ThreadSanitizer: data race (pid=35190)
>   Read of size 8 at 0x7d3000027290 by main thread:
>     #0 gomp_iter_dynamic_next
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/iter.c:190
> (libgomp.so.1+0x000000006678)
>     #1 GOMP_loop_dynamic_start
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/loop.c:128
> (libgomp.so.1+0x000000007a03)
>     #2 MAIN__._omp_fn.0 test.f90:0 (exe+0x000000000d7d)
>     #3 MAIN__ test.f90:0 (exe+0x000000000ccb)
>     #4 main ??:0 (exe+0x000000000d1a)
>
>   Previous write of size 8 at 0x7d3000027290 by thread 1:
>     #0 gomp_loop_init
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/loop.c:41
> (libgomp.so.1+0x000000007a96)
>     #1 MAIN__._omp_fn.0 test.f90:0 (exe+0x000000000d7d)
>     #2 gomp_thread_start
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/team.c:116
> (libgomp.so.1+0x00000000d012)
>
>   Location is heap block of size 1568 at 0x7d3000027100 allocated by main
> thread:
>     #0 malloc ??:0 (libtsan.so.0+0x00000001896e)
>     #1 gomp_malloc
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/alloc.c:36
> (libgomp.so.1+0x00000000417a)
>     #2 gomp_new_team
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/team.c:145
> (libgomp.so.1+0x00000000d27a)
>     #3 GOMP_parallel_start
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/parallel.c:108
> (libgomp.so.1+0x00000000afc7)
>     #4 MAIN__ test.f90:0 (exe+0x000000000cc1)
>     #5 main ??:0 (exe+0x000000000d1a)
>
>   Thread 1 (tid=35191, running) created at:
>     #0 pthread_create ??:0 (libtsan.so.0+0x00000001a868)
>     #1 gomp_team_start
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/team.c:440
> (libgomp.so.1+0x00000000d908)
>     #2 GOMP_parallel_start
> /data/vjoost/gnu/gcc_trunk/obj/x86_64-unknown-linux-gnu/libgomp/../../../gcc/libgomp/parallel.c:108
> (libgomp.so.1+0x00000000afd7)
>     #3 MAIN__ test.f90:0 (exe+0x000000000cc1)
>     #4 main ??:0 (exe+0x000000000d1a)


Looks like unsafe publication of gomp_work_share data.

Can you show disassembly of
>     #2 MAIN__._omp_fn.0 test.f90:0 (exe+0x000000000d7d)
?
How does it choose between calling gomp_loop_init() and
GOMP_loop_dynamic_start()?

Humm... do omp generated functions (like MAIN__._omp_fn.0) pass
through tsan pass? Perhaps it contains some atomic op that tsan does
not see.