https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100144
Bug ID: 100144
Summary: [OpenMP] Data race with "omp parallel master taskloop
... shared(scalar)"
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Keywords: openmp
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
CC: jakub at gcc dot gnu.org
Target Milestone: ---
That's SOLLVE_VV's
https://github.com/SOLLVE/sollve_vv/blob/master/tests/5.0/parallel_master_taskloop/test_parallel_master_taskloop.c#L31
The code uses:
int num_threads = -1;
...
#pragma omp parallel master taskloop num_threads(OMPVV_NUM_THREADS_HOST)
shared(x, y, z, num_threads)
for (int i = 0; i < N; i++) {
x[i] += y[i]*z[i];
if (omp_get_thread_num() == 0) {
num_threads = omp_get_num_threads();
}
}
Here: N = 1024, OMPVV_NUM_THREADS_HOST = 8 - and, hence,
"omp_get_thread_num() == 0" → 128 times true.
For num_threads:
* Result: -1 (initial value) or 8
* Expected: always >= 0, in particular == 8
The race also occurs when the assignment is surrounded by 'omp atomic write' or
'omp critical' surrounding the assignment (occurs quickly) or around the whole
for-block (did not see it, but TSAN reports this).
