Hi! On 2022-01-31T19:13:09+0000, Hafiz Abid Qadeer <abid_qad...@mentor.com> wrote: > On 25/01/2022 10:32, Tobias Burnus wrote: >> On 25.01.22 10:19, Thomas Schwinge wrote: >>>> I am trying to figure out if the problem you observed >>>> is a general one or just specific to fortran testcase. >>> So, unless the '-fsanitize=thread' issues are bogus -- unlikely ;-) -- it >>> seems a latent issue generally, now fatal with >>> 'libgomp.fortran/allocate-1.f90'. >> >> There is one known issue with libgomp and TSAN (-fsanitize=thread) >> that I tend to forget about :-( >> >> That's according to Jakub, who wrote a while ago: >> >> "TSAN doesn't understand what libgomp is doing, unless built with >> --disable-linux-futex"
Uh. Anything that can reasonably be done to address this? At least, to make this obvious to the user of '-fsanitize=thread'? >> However, I now tried to disable futex and still get the following. >> (First result for libgomp.c-c++-common/allocate-1.c). >> >> On the other hand, I have the feeling that the configure option is >> a no op for libgomp. This can also be seen in the configure.ac script, >> which only for libstdc++ uses the result and the others have a no-op >> call to 'true' (alias ':'): >> >> libgomp/configure.ac:GCC_LINUX_FUTEX(:) >> libitm/configure.ac:GCC_LINUX_FUTEX(:) >> libstdc++-v3/configure.ac:GCC_LINUX_FUTEX([AC_DEFINE(HAVE_LINUX_FUTEX, 1, >> [Define if futex syscall >> is available.])]) >> >> (The check is not completely pointless as some checks are still done; >> e.g. 'SYS_gettid and SYS_futex required'.) Uh. That (make '--disable-linux-futex' work) should be fixed, I suppose? >> (TSAN did find issues in libgomp in the past, however. But those >> habe been fixed.) >> >> >> Thus, there might or might not be an issue when TSAN reports one. >> >> * * * >> >> Glancing at the Fortran testcase, I noted the following, >> which probably does not cause the problems. But still, >> I want to mention it: >> >> !$omp parallel private (y, v) firstprivate (x) allocate (x, y, v) >> if (x /= 42) then >> stop 1 >> end if >> >> v(1) = 7 >> if ( (and(fl, 2) /= 0) .and. & >> ((is_64bit_aligned(x) == 0) .or. & >> (is_64bit_aligned(y) == 0) .or. & >> (is_64bit_aligned(v(1)) == 0))) then >> stop 2 >> end if >> >> If one compares this with the C/C++ testcase, I note that there >> is a barrier before the alignment check in C/C++ but not in >> Fortran. Additionally, 'v(1) = 7' is set twice and the >> alignment check happens earlier than in C/C++. Not that that >> should really matter, but I just saw it. >> >> >> In C/C++: >> int v[x], w[x]; >> ... >> v[0] = 7; >> v[41] = 8; >> >> In Fortran: >> integer, dimension(x) :: v >> ... >> v(1) = 7 >> v(41) = 8 >> >> where 'x == 42'. The Fortran version is not really wrong, but I think >> the idea is to set the first and last array element - and that's here >> v(42) and not v(41). >> >> BTW: Fortran permits to specify a different lower bound. When converting >> C/C++ testcases, it can be useful to use the same lower bound also in >> Fortran: integer :: v(0:x-1) (or: 'integer, dimension(0:x-1) :: v') >> uses then 0 ... 41 for the indices instead of 1 ... 42. >> >> But one has to be careful as Fortran uses the upper bound and C uses the >> number of elements. (Same with OpenMP array sections in Fortran vs. C.) Abid, are you going to address these? I think it does make sense if the C/C++ and Fortran test cases match as much as feasible. >> PS: The promised data-race warning: >> ================== >> WARNING: ThreadSanitizer: data race (pid=4135381) >> Read of size 8 at 0x7ffc0888bdc0 by thread T10: >> #0 foo._omp_fn.2 libgomp.c-c++-common/allocate-1.c:47 (a.out+0x402c05) >> #1 gomp_thread_start ../../../repos/gcc/libgomp/team.c:129 >> (libgomp.so.1+0x1e5ed) >> >> Previous write of size 8 at 0x7ffc0888bdc0 by main thread: >> #0 foo._omp_fn.1 libgomp.c-c++-common/allocate-1.c:47 (a.out+0x402aee) >> #1 GOMP_teams_reg ../../../repos/gcc/libgomp/teams.c:51 >> (libgomp.so.1+0x3638c) >> #2 main libgomp.c-c++-common/allocate-1.c:366 (a.out+0x40273e) >> >> Location is stack of main thread. >> >> Location is global '<null>' at 0x000000000000 ([stack]+0x1ddc0) >> >> Thread T10 (tid=4135398, running) created by main thread at: >> #0 pthread_create >> ../../../../repos/gcc/libsanitizer/tsan/tsan_interceptors_posix.cpp:1001 >> (libtsan.so.2+0x62c76) >> #1 gomp_team_start ../../../repos/gcc/libgomp/team.c:858 >> (libgomp.so.1+0x1ec18) >> #2 main libgomp.c-c++-common/allocate-1.c:366 (a.out+0x40273e) >> >> SUMMARY: ThreadSanitizer: data race libgomp.c-c++-common/allocate-1.c:47 in >> foo._omp_fn.2 >> ================== >> > > Problem was with the pool_size trait. It has limited size which this testcase > exceeded. I have > removed it now which seems to fix the problem. Ok to commit the attached > patch? First, I do confirm that this (testing together with Tobias' patch "which silences the three kind of warnings and fixes the interface issue" plus my suggestion that the "early 'stop' [...] be backed out") does resolve the execution FAILs, thanks. However: really (a) remove 'omp_alloctrait (omp_atk_pool_size, 8192)' altogether, or instead: (b) increase its size (if that can be computed) -- and/or (c) limit the number of OpenMP threads executing in parallel? Due to unfamiliarity with all that, I don't know what's best here. Grüße Thomas > From 98b5493bd94520dd78b3963d3a4e67cba6bfb6aa Mon Sep 17 00:00:00 2001 > From: Hafiz Abid Qadeer <ab...@codesourcery.com> > Date: Mon, 31 Jan 2022 19:02:14 +0000 > Subject: [PATCH] [libgomp] Fix testcase to remove out of memory error. > > Thomas reported in > https://gcc.gnu.org/pipermail/gcc-patches/2022-January/589039.html > that this testcase is randomly failing. The problem was fixed pool > size which was exhausted when there were a lot of threads. Fixed it > by removing pool_size trait which causes default pool size to be used > which should be big enough. > > libgomp/ChangeLog: > > * testsuite/libgomp.fortran/allocate-1.f90: Remove pool_size trait. > --- > libgomp/testsuite/libgomp.fortran/allocate-1.f90 | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/libgomp/testsuite/libgomp.fortran/allocate-1.f90 > b/libgomp/testsuite/libgomp.fortran/allocate-1.f90 > index 35d1750b878..04bf2307462 100644 > --- a/libgomp/testsuite/libgomp.fortran/allocate-1.f90 > +++ b/libgomp/testsuite/libgomp.fortran/allocate-1.f90 > @@ -313,13 +313,12 @@ program main > integer, dimension(4) :: p > integer, dimension(4) :: q > > - type (omp_alloctrait) :: traits(3) > + type (omp_alloctrait) :: traits(2) > integer (omp_allocator_handle_kind) :: a > > traits = [omp_alloctrait (omp_atk_alignment, 64), & > - omp_alloctrait (omp_atk_fallback, omp_atv_null_fb), & > - omp_alloctrait (omp_atk_pool_size, 8192)] > - a = omp_init_allocator (omp_default_mem_space, 3, traits) > + omp_alloctrait (omp_atk_fallback, omp_atv_null_fb)] > + a = omp_init_allocator (omp_default_mem_space, 2, traits) > if (a == omp_null_allocator) stop 1 > > call omp_set_default_allocator (omp_default_mem_alloc); > -- > 2.25.1 ----------------- Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634 München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht München, HRB 106955
