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Subject: [Bug dynamic-link/19329] dl-tls.c assert failure at concurrent
 pthread_create and dlopen
Date: Mon, 04 Oct 2021 14:12:03 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D19329

--- Comment #43 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot g=
nu.org> ---
The master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=3Dglibc.git;h=3D83b5323261bb72313bf=
fcf37476c1b8f0847c736

commit 83b5323261bb72313bffcf37476c1b8f0847c736
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Wed Sep 15 15:16:19 2021 +0100

    elf: Avoid deadlock between pthread_create and ctors [BZ #28357]

    The fix for bug 19329 caused a regression such that pthread_create can
    deadlock when concurrent ctors from dlopen are waiting for it to finish.
    Use a new GL(dl_load_tls_lock) in pthread_create that is not taken
    around ctors in dlopen.

    The new lock is also used in __tls_get_addr instead of GL(dl_load_lock).

    The new lock is held in _dl_open_worker and _dl_close_worker around
    most of the logic before/after the init/fini routines.  When init/fini
    routines are running then TLS is in a consistent, usable state.
    In _dl_open_worker the new lock requires catching and reraising dlopen
    failures that happen in the critical section.

    The new lock is reinitialized in a fork child, to keep the existing
    behaviour and it is kept recursive in case malloc interposition or TLS
    access from signal handlers can retake it.  It is not obvious if this
    is necessary or helps, but avoids changing the preexisting behaviour.

    The new lock may be more appropriate for dl_iterate_phdr too than
    GL(dl_load_write_lock), since TLS state of an incompletely loaded
    module may be accessed.  If the new lock can replace the old one,
    that can be a separate change.

    Fixes bug 28357.

    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

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