Remove unnecessary locking when reading iconv configuration [BZ #22062]

In iconv/gconv_conf.c, __gconv_get_path unnecessarily obtains a lock when
populating the array pointed to by __gconv_path_elem. The locking is not
necessary because all calls to __gconv_read_conf (which in turn calls
__gconv_get_path) are serialized using __libc_once.

This patch:
- removes all locking in __gconv_get_path;
- replaces all explicitly serialized __gconv_read_conf calls with calls to
  __gconv_load_conf, a new wrapper that is serialized internally;
- adds a new test, iconv/tst-iconv_mt.c, to exercise iconv initialization,
  usage, and cleanup in a multi-threaded program;
- indents __gconv_get_path correctly, removing tab characters (which makes
  the patch look a little bigger than it really is).

After removing the unnecessary locking, it was confirmed that the test case
fails if the relevant __libc_once is removed. Additionally, four localedata
and iconvdata tests also fail. This gives confidence that the testsuite
sufficiently guards against some regressions relating to multi-threading
with iconv.

Tested on x86_64 and i686.

1 files changed, 142 insertions, 0 deletions

diff --git a/iconv/tst-iconv-mt.c b/iconv/tst-iconv-mt.c
new file mode 100644
index 0000000..aa91a98
--- /dev/null
+++ b/iconv/tst-iconv-mt.c
@@ -0,0 +1,142 @@
+/* Test that iconv works in a multi-threaded program.
+   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/>.  */
+
+/* This test runs several worker threads that perform the following three
+   steps in staggered synchronization with each other:
+   1. initialization (iconv_open)
+   2. conversion (iconv)
+   3. cleanup (iconv_close)
+   Having several threads synchronously (using pthread_barrier_*) perform
+   these routines exercises iconv code that handles concurrent attempts to
+   initialize and/or read global iconv state (namely configuration).  */
+
+#include <iconv.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <support/support.h>
+#include <support/xthread.h>
+#include <support/check.h>
+
+#define TCOUNT 16
+_Static_assert (TCOUNT %2 == 0,
+                "thread count must be even, since we need two groups.");
+
+
+#define CONV_INPUT "Hello, iconv!"
+
+
+pthread_barrier_t sync;
+pthread_barrier_t sync_half_pool;
+
+
+/* Execute iconv_open, iconv and iconv_close in a synchronized way in
+   conjunction with other sibling worker threads.  If any step fails, print
+   an error to stdout and return NULL to the main thread to indicate the
+   error.  */
+static void *
+worker (void * arg)
+{
+  long int tidx = (long int) arg;
+
+  iconv_t cd;
+
+  char ascii[] = CONV_INPUT;
+  char *inbufpos = ascii;
+  size_t inbytesleft = sizeof (CONV_INPUT);
+
+  char *utf8 = xcalloc (sizeof (CONV_INPUT), 1);
+  char *outbufpos = utf8;
+  size_t outbytesleft = sizeof (CONV_INPUT);
+
+  if (tidx < TCOUNT/2)
+    /* The first half of the worker thread pool synchronize together here,
+       then call iconv_open immediately after.  */
+    xpthread_barrier_wait (&sync_half_pool);
+  else
+    /* The second half wait for the first half to finish iconv_open and
+       continue to the next barrier (before the call to iconv below).  */
+    xpthread_barrier_wait (&sync);
+
+  /* The above block of code staggers all subsequent pthread_barrier_wait
+     calls in a way that ensures a high chance of encountering these
+     combinations of concurrent iconv usage:
+     1) concurrent calls to iconv_open,
+     2) concurrent calls to iconv_open *and* iconv,
+     3) concurrent calls to iconv,
+     4) concurrent calls to iconv *and* iconv_close,
+     5) concurrent calls to iconv_close.  */
+
+  cd = iconv_open ("UTF8", "ASCII");
+  TEST_VERIFY_EXIT (cd != (iconv_t) -1);
+
+  xpthread_barrier_wait (&sync);
+
+  TEST_VERIFY_EXIT (iconv (cd, &inbufpos, &inbytesleft, &outbufpos,
+                           &outbytesleft)
+                    != (size_t) -1);
+
+  *outbufpos = '\0';
+
+  xpthread_barrier_wait (&sync);
+
+  TEST_VERIFY_EXIT (iconv_close (cd) == 0);
+
+  /* The next conditional barrier wait is needed because we staggered the
+     threads into two groups in the beginning and at this point, the second
+     half of worker threads are waiting for the first half to finish
+     iconv_close before they can executing the same:  */
+  if (tidx < TCOUNT/2)
+    xpthread_barrier_wait (&sync);
+
+  if (strncmp (utf8, CONV_INPUT, sizeof CONV_INPUT))
+    {
+      printf ("FAIL: thread %lx: invalid conversion output from iconv\n", tidx);
+      pthread_exit ((void *) (long int) 1);
+    }
+
+  pthread_exit (NULL);
+}
+
+
+static int
+do_test (void)
+{
+  pthread_t thread[TCOUNT];
+  void * worker_output;
+  int i;
+
+  xpthread_barrier_init (&sync, NULL, TCOUNT);
+  xpthread_barrier_init (&sync_half_pool, NULL, TCOUNT/2);
+
+  for (i = 0; i < TCOUNT; i++)
+    thread[i] = xpthread_create (NULL, worker, (void *) (long int) i);
+
+  for (i = 0; i < TCOUNT; i++)
+    {
+      worker_output = xpthread_join (thread[i]);
+      TEST_VERIFY_EXIT (worker_output == NULL);
+    }
+
+  xpthread_barrier_destroy (&sync);
+  xpthread_barrier_destroy (&sync_half_pool);
+
+  return 0;
+}
+
+#include <support/test-driver.c>