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, 16 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 0f3a846ad3..19466c18db 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2018-10-17  Arjun Shankar  <arjun@redhat.com>
+
+	[BZ #22062]
+	* iconv/gconv_conf.c (__gconv_get_path): Remove locking and fix
+	indentation.
+	* (__gconv_read_conf): Mark function static.
+	* (once): New static variable.
+	* (__gconv_load_conf): New function.
+	* iconv/gconv_int.h (__gconv_load_conf): Likewise.
+	* iconv/gconv_db.c (once): Remove static variable.
+	* (__gconv_compare_alias): Use __gconv_load_conf instead of
+	__gconv_read_conf.
+	* (__gconv_find_transform): Likewise.
+	* iconv/tst-iconv-mt.c: New test.
+	* iconv/Makefile: Add tst-iconv_mt.
+
 2018-10-17  Joseph Myers  <joseph@codesourcery.com>
 
 	* sysdeps/unix/sysv/linux/Makefile (sysdep_headers): Add