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

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

[schwab@linux-m68k.org]

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

            Bug ID: 25942
           Summary: Deadlock on stack_cache_lock between __nptl_setxid and
                    exiting detached thread
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: nptl
          Assignee: unassigned at sourceware dot org
          Reporter: schwab@linux-m68k.org
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

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, but for detached threads it goes on to deallocate the
stack right away.

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

[schwab@linux-m68k.org]

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

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |2.32

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> ---
Fixed in 2.32.

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[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
----------------------------------------------------------------------------
                 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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