Fix incorrect double-checked locking related to _res_hconf.initialized.

_res_hconf.initialized was not suitable for use in a multi-threaded
environment due to the lack of atomics and memory barriers.  Use of it was
also unnecessary because _res_hconf_init did the right thing by using
__libc_once.  This patch fixes the glibc-internal uses by just calling
_res_hconf_init unconditionally, and switches to a release MO atomic store
for _res_hconf.initialized to fix the glibc side of the synchronization
problem (which will maintain backward compatibility, but cannot fix the
lack of acquire MO on any glibc-external loads).

	[BZ #20477]
	* resolv/res_hconf.c (do_init): Use atomic access.
	* resolv/res_hconf.h: Add comments.
	* nscd/aicache.c (addhstaiX): Call _res_hconf_init unconditionally.
	* nss/getXXbyYY_r.c (REENTRANT_NAME): Likewise.
	* sysdeps/posix/getaddrinfo.c (gaih_inet): Likewise.

1 files changed, 2 insertions, 1 deletions

diff --git a/resolv/res_hconf.c b/resolv/res_hconf.c
index 5cd128916d..093c26837f 100644
--- a/resolv/res_hconf.c
+++ b/resolv/res_hconf.c
@@ -348,7 +348,8 @@ do_init (void)
       arg_trimdomain_list (ENV_TRIM_OVERR, 1, envval);
     }
 
-  _res_hconf.initialized = 1;
+  /* See comments on the declaration of _res_hconf.  */
+  atomic_store_release (&_res_hconf.initialized, 1);
 }