sysconf: Use conservative default for _SC_NPROCESSORS_ONLN [BZ #21542]

ChangeLog

@@ -1,3 +1,11 @@
+2017-07-04  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #21542]
+	* sysdeps/unix/sysv/linux/getsysstats.c (__get_nprocs): Default to
+	two if no accurate information is available.
+	* posix/tst-sysconf-empty-chroot.c: New file.
+	* posix/Makefile (tests): Add it.
+
 2017-07-04  Florian Weimer  <fweimer@redhat.com>
 
 	* resolv/resolv_conf.c (resolv_conf_matches): Tighten check for name

posix/Makefile

@@ -92,7 +92,8 @@ tests		:= test-errno tstgetopt testfnm runtests runptests \
 		   tst-pathconf tst-getaddrinfo4 tst-rxspencer-no-utf8 \
 		   tst-fnmatch3 bug-regex36 tst-getaddrinfo5 \
 		   tst-posix_spawn-fd tst-posix_spawn-setsid \
-		   tst-posix_fadvise tst-posix_fadvise64
+		   tst-posix_fadvise tst-posix_fadvise64 \
+		   tst-sysconf-empty-chroot
 tests-internal	:= bug-regex5 bug-regex20 bug-regex33 \
 		   tst-rfc3484 tst-rfc3484-2 tst-rfc3484-3
 xtests		:= bug-ga2

posix/tst-sysconf-empty-chroot.c

@@ -0,0 +1,95 @@
+/* Test sysconf with an empty chroot.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+#include <unistd.h>
+
+/* Check for an SMP system in a forked process, so that the parent
+   process does not cache the value.  */
+static void
+is_smp_callback (void *closure)
+{
+  bool *result = closure;
+
+  long cpus = sysconf (_SC_NPROCESSORS_ONLN);
+  TEST_VERIFY_EXIT (cpus > 0);
+  *result = cpus != 1;
+}
+
+static bool
+is_smp (void)
+{
+  bool *result = support_shared_allocate (sizeof (*result));
+  support_isolate_in_subprocess (is_smp_callback, result);
+  bool result_copy = *result;
+  support_shared_free (result);
+  return result_copy;
+}
+
+static char *path_chroot;
+
+/* Prepare an empty directory, to be used as a chroot.  */
+static void
+prepare (int argc, char **argv)
+{
+  path_chroot = xasprintf ("%s/tst-resolv-res_init-XXXXXX", test_dir);
+  if (mkdtemp (path_chroot) == NULL)
+    FAIL_EXIT1 ("mkdtemp (\"%s\"): %m", path_chroot);
+  add_temp_file (path_chroot);
+}
+
+/* The actual test.  Run it in a subprocess, so that the test harness
+   can remove the temporary directory in --direct mode.  */
+static void
+chroot_callback (void *closure)
+{
+  xchroot (path_chroot);
+  long cpus = sysconf (_SC_NPROCESSORS_ONLN);
+  printf ("info: sysconf (_SC_NPROCESSORS_ONLN) in chroot: %ld\n", cpus);
+  TEST_VERIFY (cpus > 0);
+  TEST_VERIFY (cpus != 1);
+  _exit (0);
+}
+
+static int
+do_test (void)
+{
+  if (!is_smp ())
+    {
+      printf ("warning: test not supported on uniprocessor system\n");
+      return EXIT_UNSUPPORTED;
+    }
+
+  support_become_root ();
+  if (!support_can_chroot ())
+    return EXIT_UNSUPPORTED;
+
+  support_isolate_in_subprocess (chroot_callback, NULL);
+
+  return 0;
+}
+
+#define PREPARE prepare
+#include <support/test-driver.c>

sysdeps/unix/sysv/linux/getsysstats.c

@@ -188,7 +188,10 @@ __get_nprocs (void)
 
   cp = buffer_end;
   re = buffer_end;
-  result = 1;
+
+  /* Default to an SMP system in case we cannot obtain an accurate
+     number.  */
+  result = 2;
 
   /* The /proc/stat format is more uniform, use it by default.  */
   fd = open_not_cancel_2 ("/proc/stat", flags);