[PATCH Fix incorrect double-checked locking related to _res_hconf.initialized. [BZ #20477]

[Florian Weimer]

On 08/17/2016 02:15 PM, Torvald Riegel wrote:
> _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.

Looks good to me.  Please commit.

Thanks,
Florian