Add reproducer test for crash after fork

See #2993 for an analysis

utest/CMakeLists.txt

@@ -27,13 +27,17 @@ endif ()
 
 # known to hang with the native Windows and Android threads
 # FIXME needs checking if this works on any of the other platforms
-if (NOT USE_OPENMP)
 if (OS_CYGWIN_NT OR OS_LINUX)
+if (NOT USE_OPENMP)
 set(OpenBLAS_utest_src
   ${OpenBLAS_utest_src}
   test_fork.c
   )
 endif()
+set(OpenBLAS_utest_src
+  ${OpenBLAS_utest_src}
+  test_post_fork.c
+  )
 endif()
 
 if (NOT NO_LAPACK)

utest/Makefile

@@ -25,10 +25,11 @@ endif
 
 #this does not work with OpenMP nor with native Windows or Android threads
 # FIXME TBD if this works on OSX, SunOS, POWER and zarch
-ifndef USE_OPENMP
 ifeq ($(OSNAME), $(filter $(OSNAME),Linux CYGWIN_NT))
+ifneq ($(USE_OPENMP), 1)
 OBJS += test_fork.o
 endif
+OBJS += test_post_fork.o
 endif
 
 ifeq ($(C_COMPILER), PGI)

utest/test_fork.c

@@ -36,7 +36,7 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <cblas.h>
 #include "openblas_utest.h"
 
-void* xmalloc(size_t n)
+static void* xmalloc(size_t n)
 {
     void* tmp;
     tmp = malloc(n);
@@ -49,7 +49,7 @@ void* xmalloc(size_t n)
 }
 
 #ifdef BUILD_DOUBLE
-void check_dgemm(double *a, double *b, double *result, double *expected, blasint n)
+static void check_dgemm(double *a, double *b, double *result, double *expected, blasint n)
 {
     char trans1 = 'T';
     char trans2 = 'N';

utest/test_post_fork.c

@@ -0,0 +1,131 @@
+/*****************************************************************************
+Copyright (c) 2011-2020, The OpenBLAS Project
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   1. Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+   2. Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in
+      the documentation and/or other materials provided with the
+      distribution.
+   3. Neither the name of the OpenBLAS project nor the names of
+      its contributors may be used to endorse or promote products
+      derived from this software without specific prior written
+      permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+**********************************************************************************/
+
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <cblas.h>
+#ifdef USE_OPENMP
+#include <omp.h>
+#endif
+#include "openblas_utest.h"
+
+static void* xmalloc(size_t n)
+{
+    void* tmp;
+    tmp = malloc(n);
+    if (tmp == NULL) {
+        fprintf(stderr, "You are about to die\n");
+        exit(1);
+    } else {
+        return tmp;
+    }
+}
+
+#ifdef BUILD_DOUBLE
+static void check_dgemm(double *a, double *b, double *result, double *expected, blasint n)
+{
+    char trans1 = 'T';
+    char trans2 = 'N';
+    double zerod = 0, oned = 1;
+    int i;
+    BLASFUNC(dgemm)(&trans1, &trans2, &n, &n, &n, &oned, a, &n, b, &n, &zerod, result, &n);
+    for(i = 0; i < n * n; ++i) {
+        ASSERT_DBL_NEAR_TOL(expected[i], result[i], DOUBLE_EPS);
+    }
+}
+#endif
+
+CTEST(fork, safety_after_fork_in_parent)
+{
+#ifndef BUILD_DOUBLE
+exit(0);
+#else
+    blasint n = 100;
+    int i, nthreads_omp;
+
+    double *a, *b, *c, *d;
+    size_t n_bytes;
+
+    pid_t fork_pid;
+
+    n_bytes = sizeof(*a) * n * n;
+
+    a = xmalloc(n_bytes);
+    b = xmalloc(n_bytes);
+    c = xmalloc(n_bytes);
+    d = xmalloc(n_bytes);
+
+    // Put ones in a, b and n in c (result)
+    for(i = 0; i < n * n; ++i) {
+        a[i] = 1;
+        b[i] = 1;
+        c[i] = 1 * n;
+    }
+
+    // Test that OpenBLAS works after a fork.
+    // This situation routinely happens with Pythons numpy where a
+    // `sys.platform` calls `uname` in a forked process.
+    // So we simulate this situation here.
+
+    // There was an issue where a different number of OpenBLAS and OpenMP
+    // threads triggered a memory leak. So run this multiple times
+    // with different number of threads set.
+#ifdef USE_OPENMP
+    nthreads_omp = omp_get_max_threads();
+    // Run with half the max OMP threads, the max threads and twice that
+    for(i = (nthreads_omp + 1) / 2; i <= nthreads_omp * 2; i *= 2) {
+        omp_set_num_threads(i);
+#endif
+
+        fork_pid = fork();
+        if (fork_pid == -1) {
+            CTEST_ERR("Failed to fork process.");
+        } else if (fork_pid == 0) {
+            // Just pretend to do something, e.g. call `uname`, then exit
+            exit(0);
+        } else {
+            // Wait for the child to finish and check the exit code.
+            int child_status = 0;
+            pid_t wait_pid = wait(&child_status);
+            ASSERT_EQUAL(wait_pid, fork_pid);
+            ASSERT_EQUAL(0, WEXITSTATUS (child_status));
+
+            // Now OpenBLAS has to work
+            check_dgemm(a, b, d, c, n);
+        }
+#ifdef USE_OPENMP
+    }
+#endif
+
+#endif
+}