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, 2 insertions, 6 deletions

diff --git a/iconv/gconv_db.c b/iconv/gconv_db.c
index 66e095d8c7..86acfc7d74 100644
--- a/iconv/gconv_db.c
+++ b/iconv/gconv_db.c
@@ -687,10 +687,6 @@ find_derivation (const char *toset, const char *toset_expand,
 }
 
 
-/* Control of initialization.  */
-__libc_once_define (static, once);
-
-
 static const char *
 do_lookup_alias (const char *name)
 {
@@ -709,7 +705,7 @@ __gconv_compare_alias (const char *name1, const char *name2)
   int result;
 
   /* Ensure that the configuration data is read.  */
-  __libc_once (once, __gconv_read_conf);
+  __gconv_load_conf ();
 
   if (__gconv_compare_alias_cache (name1, name2, &result) != 0)
     result = strcmp (do_lookup_alias (name1) ?: name1,
@@ -729,7 +725,7 @@ __gconv_find_transform (const char *toset, const char *fromset,
   int result;
 
   /* Ensure that the configuration data is read.  */
-  __libc_once (once, __gconv_read_conf);
+  __gconv_load_conf ();
 
   /* Acquire the lock.  */
   __libc_lock_lock (__gconv_lock);