[Bug network/20477] resolv: incorrect double-checked locking related to _res_hconf

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https://sourceware.org/bugzilla/show_bug.cgi?id=20477

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6f9d4f595e4073807ad0e844cbb3b3d7158b76d5

commit 6f9d4f595e4073807ad0e844cbb3b3d7158b76d5
Author: Torvald Riegel <triegel@redhat.com>
Date:   Wed Aug 17 13:56:11 2016 +0200

    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.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                   |    9 +++++++++
 nscd/aicache.c              |    3 +--
 nss/getXXbyYY_r.c           |    3 +--
 resolv/res_hconf.c          |    3 ++-
 resolv/res_hconf.h          |    9 +++++++++
 sysdeps/posix/getaddrinfo.c |    3 +--
 6 files changed, 23 insertions(+), 7 deletions(-)

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