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[Bug nptl/19402] Deadlock with robust shared mutex and asynchronous termination

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- Log -----------------------------------------------------------------;h=8e31cafb268938729a1314806a924d73fb1991c5

commit 8e31cafb268938729a1314806a924d73fb1991c5
Author: Torvald Riegel <>
Date:   Wed Dec 21 13:37:19 2016 +0100

    Clear list of acquired robust mutexes in the child process after forking.

    Robust mutexes acquired at the time of a call to fork() do not remain
    acquired by the forked child process.  We have to clear the list of
    acquired robust mutexes before registering this list with the kernel;
    otherwise, if some of the robust mutexes are process-shared, the parent
    process can alter the child's robust mutex list, which can lead to
    deadlocks or even modification of memory that may not be occupied by a
    mutex anymore.

        [BZ #19402]
        * sysdeps/nptl/fork.c (__libc_fork): Clear list of acquired robust

commit 65810f0ef05e8c9e333f17a44e77808b163ca298
Author: Torvald Riegel <>
Date:   Thu Dec 22 10:20:43 2016 +0100

    robust mutexes: Fix broken x86 assembly by removing it

    lll_robust_unlock on i386 and x86_64 first sets the futex word to
    FUTEX_WAITERS|0 before calling __lll_unlock_wake, which will set the
    futex word to 0.  If the thread is killed between these steps, then the
    futex word will be FUTEX_WAITERS|0, and the kernel (at least current
    upstream) will not set it to FUTEX_OWNER_DIED|FUTEX_WAITERS because 0 is
    not equal to the TID of the crashed thread.

    The lll_robust_lock assembly code on i386 and x86_64 is not prepared to
    deal with this case because the fastpath tries to only CAS 0 to TID and
    not FUTEX_WAITERS|0 to TID; the slowpath simply waits until it can CAS 0
    to TID or the futex_word has the FUTEX_OWNER_DIED bit set.

    This issue is fixed by removing the custom x86 assembly code and using
    the generic C code instead.  However, instead of adding more duplicate
    code to the custom x86 lowlevellock.h, the code of the lll_robust*
    is inlined into the single call sites that exist for each of these
    in the pthread_mutex_* functions.  The robust mutex paths in the latter
    have been slightly reorganized to make them simpler.

    This patch is meant to be easy to backport, so C11-style atomics are not

        [BZ #20985]
        * nptl/Makefile: Adapt.
        * nptl/pthread_mutex_cond_lock.c (LLL_ROBUST_MUTEX_LOCK): Remove.
        * nptl/pthread_mutex_lock.c (LLL_ROBUST_MUTEX_LOCK): Remove.
        (__pthread_mutex_lock_full): Inline lll_robust* functions and adapt.
        * nptl/pthread_mutex_timedlock.c (pthread_mutex_timedlock): Inline
        lll_robust* functions and adapt.
        * nptl/pthread_mutex_unlock.c (__pthread_mutex_unlock_full): Likewise.
        * sysdeps/nptl/lowlevellock.h (__lll_robust_lock_wait,
        __lll_robust_lock, lll_robust_cond_lock, __lll_robust_timedlock_wait,
        __lll_robust_timedlock, __lll_robust_unlock): Remove.
        * sysdeps/unix/sysv/linux/i386/lowlevellock.h (lll_robust_lock,
        lll_robust_cond_lock, lll_robust_timedlock, lll_robust_unlock): Remove.
        * sysdeps/unix/sysv/linux/x86_64/lowlevellock.h (lll_robust_lock,
        lll_robust_cond_lock, lll_robust_timedlock, lll_robust_unlock): Remove.
        * sysdeps/unix/sysv/linux/sparc/lowlevellock.h (__lll_robust_lock_wait,
        __lll_robust_lock, lll_robust_cond_lock, __lll_robust_timedlock_wait,
        __lll_robust_timedlock, __lll_robust_unlock): Remove.
        * nptl/lowlevelrobustlock.c: Remove file.
        * nptl/lowlevelrobustlock.sym: Likewise.
        * sysdeps/unix/sysv/linux/i386/lowlevelrobustlock.S: Likewise.
        * sysdeps/unix/sysv/linux/x86_64/lowlevelrobustlock.S: Likewise.


Summary of changes:
 ChangeLog                                          |   33 ++
 nptl/Makefile                                      |    4 +-
 nptl/lowlevelrobustlock.c                          |  136 ---------
 nptl/lowlevelrobustlock.sym                        |    6 -
 nptl/pthread_mutex_cond_lock.c                     |    6 +-
 nptl/pthread_mutex_lock.c                          |   79 ++++--
 nptl/pthread_mutex_timedlock.c                     |  106 ++++++--
 nptl/pthread_mutex_unlock.c                        |   18 +-
 sysdeps/nptl/fork.c                                |   20 +-
 sysdeps/nptl/lowlevellock.h                        |   68 -----
 sysdeps/unix/sysv/linux/i386/lowlevellock.h        |   60 ----
 sysdeps/unix/sysv/linux/i386/lowlevelrobustlock.S  |  232 ---------------
 sysdeps/unix/sysv/linux/sparc/lowlevellock.h       |   40 ---
 sysdeps/unix/sysv/linux/x86_64/lowlevellock.h      |   74 -----
 .../unix/sysv/linux/x86_64/lowlevelrobustlock.S    |  306 --------------------
 15 files changed, 205 insertions(+), 983 deletions(-)
 delete mode 100644 nptl/lowlevelrobustlock.c
 delete mode 100644 nptl/lowlevelrobustlock.sym
 delete mode 100644 sysdeps/unix/sysv/linux/i386/lowlevelrobustlock.S
 delete mode 100644 sysdeps/unix/sysv/linux/x86_64/lowlevelrobustlock.S

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