http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55561
--- Comment #21 from Dmitry Vyukov <dvyukov at google dot com> 2012-12-29 10:21:06 UTC --- It is a known issue http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40362#c7 and Jakub said it's safe. I am not that sure. On Sat, Dec 29, 2012 at 2:13 PM, dvyukov at google dot com <gcc-bugzi...@gcc.gnu.org> wrote: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55561 > > --- Comment #20 from Dmitry Vyukov <dvyukov at google dot com> 2012-12-29 > 10:13:00 UTC --- > (In reply to comment #19) >> On Wed, Dec 26, 2012 at 12:23 AM, Joost.VandeVondele at mat dot >> ethz.ch <gcc-bugzi...@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: >> > >> > vjo...@nanosim-s01.ethz.ch:/data/vjoost/clean/cp2k/cp2k/src> ./a.out >> > vjo...@nanosim-s01.ethz.ch:/data/vjoost/clean/cp2k/cp2k/src> ./a.out >> > vjo...@nanosim-s01.ethz.ch:/data/vjoost/clean/cp2k/cp2k/src> ./a.out >> > vjo...@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. > > > Congratulations! We've found racy unsafe publication in libgomp with > ThreadSanitizer: > > gomp_loop_dynamic_start() uses the following functions to synchronize with > each > other. As you can see gomp_ptrlock_get() contains fast-and-dead unsafe > fast-path. > > libgomp/config/posix/ptrlock.h > > static inline void *gomp_ptrlock_get (gomp_ptrlock_t *ptrlock) > { > if (ptrlock->ptr != NULL) > return ptrlock->ptr; > > gomp_mutex_lock (&ptrlock->lock); > if (ptrlock->ptr != NULL) > { > gomp_mutex_unlock (&ptrlock->lock); > return ptrlock->ptr; > } > > return NULL; > } > > static inline void gomp_ptrlock_set (gomp_ptrlock_t *ptrlock, void *ptr) > { > ptrlock->ptr = ptr; > gomp_mutex_unlock (&ptrlock->lock); > } > > -- > Configure bugmail: http://gcc.gnu.org/bugzilla/userprefs.cgi?tab=email > ------- You are receiving this mail because: ------- > You are on the CC list for the bug.
