[Bug nptl/25942] Deadlock on stack_cache_lock between __nptl_setxid and exiting detached thread

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=25942

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |fweimer at redhat dot com
              Flags|                            |security-

--- Comment #2 from Florian Weimer <fweimer at redhat dot com> ---
Commit:

commit 4cab20fa49b3ea3e3454fdc4f13bf3828d8efd19
Author: Andreas Schwab <schwab@suse.de>
Date:   Thu May 7 15:50:09 2020 +0200

    nptl: wait for pending setxid request also in detached thread (bug 25942)

    There is a race between __nptl_setxid and exiting detached thread, which
    causes a deadlock on stack_cache_lock.  The deadlock happens in this
    state:

    T1: setgroups -> __nptl_setxid (holding stack_cache_lock, waiting on
cmdp->cntr == 0)
    T2 (detached, exiting): start_thread -> __deallocate_stack (waiting on
stack_cache_lock)
    more threads waiting on stack_cache_lock in pthread_create

    For non-detached threads, start_thread waits for its own setxid handler to
    finish before exiting.  Do this for detached threads as well.

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