[Bug dynamic-link/27111] pthread_create and tls access use link_map objects that may be concurrently freed by dlclose

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27111

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Szabolcs Nagy <nsz@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=572bd547d57a39b6cf0ea072545dc4048921f4c3

commit 572bd547d57a39b6cf0ea072545dc4048921f4c3
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Thu Dec 31 13:59:38 2020 +0000

    elf: Fix DTV gap reuse logic [BZ #27135]

    For some reason only dlopen failure caused dtv gaps to be reused.

    It is possible that the intent was to never reuse modids for a
    different module, but after dlopen failure all gaps are reused
    not just the ones caused by the unfinished dlopened.

    So the code has to handle reused modids already which seems to
    work, however the data races at thread creation and tls access
    (see bug 19329 and bug 27111) may be more severe if slots are
    reused so this is scheduled after those fixes. I think fixing
    the races are not simpler if reuse is disallowed and reuse has
    other benefits, so set GL(dl_tls_dtv_gaps) whenever entries are
    removed from the middle of the slotinfo list. The value does
    not have to be correct: incorrect true value causes the next
    modid query to do a slotinfo walk, incorrect false will leave
    gaps and new entries are added at the end.

    Fixes bug 27135.

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

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