this deadlock just happened in CppunitTest_libreofficekit_tiledrendering:

#0  0x00007fa3811fb09d in __lll_lock_wait () at /lib64/libpthread.so.0
#1  0x00007fa3811f3e23 in pthread_mutex_lock () at /lib64/libpthread.so.0
#2  0x00007fa3822f5a16 in osl_acquireMutex(oslMutexImpl*) (pMutex=0x2d32f40) at /work/lo/master/sal/osl/unx/mutex.cxx:97
#3  0x00007fa37764b065 in osl::Mutex::acquire() (this=0x7fa36948f780 <rtl::Static<osl::Mutex, GrammarCheckingIterator::MyMutex>::get()::instance>) at /work/lo/master/include/osl/mutex.hxx:56
#4  0x00007fa3776629c2 in osl::ClearableGuard<osl::Mutex>::ClearableGuard(osl::Mutex&) (this=0x7fffcfc0df18, t=...) at /work/lo/master/include/osl/mutex.hxx:163
#5  0x00007fa3776610c5 in comphelper::OInterfaceContainerHelper2::disposeAndClear(com::sun::star::lang::EventObject const&) (this=0x7fa357bb3110, rEvt=...) at /work/lo/master/comphelper/source/container/interfacecontainer2.cxx:260
#6  0x00007fa369197174 in GrammarCheckingIterator::dispose() (this=0x7fa357bb2f50) at /work/lo/master/linguistic/source/gciterator.cxx:907
#7  0x00007fa351bd7191 in (anonymous namespace)::doDispose(com::sun::star::uno::Reference<com::sun::star::linguistic2::XProofreadingIterator> const&) (inst=uno::Reference to (GrammarCheckingIterator *) 0x7fa357bb2f78) at /work/lo/master/sw/source/core/bastyp/proofreadingiterator.cxx:34
#8  0x00007fa351bd7327 in sw::proofreadingiterator::dispose() () at /work/lo/master/sw/source/core/bastyp/proofreadingiterator.cxx:66
#9  0x00007fa351bd1d3e in FinitCore() () at /work/lo/master/sw/source/core/bastyp/init.cxx:672
#10 0x00007fa35284e394 in SwDLL::~SwDLL() (this=0x2b9b7e0, __in_chrg=<optimized out>) at /work/lo/master/sw/source/uibase/app/swdll.cxx:163
#11 0x00007fa35284f634 in std::default_delete<SwDLL>::operator()(SwDLL*) const (this=0x7fa353adea98 <rtl::Static<(anonymous namespace)::SwDLLInstance, (anonymous namespace)::theSwDLLInstance>::get()::instance+8>, __ptr=0x2b9b7e0) at /usr/include/c++/7/bits/unique_ptr.h:78
#12 0x00007fa35284f8e9 in std::unique_ptr<SwDLL, std::default_delete<SwDLL> >::reset(SwDLL*) (this=0x7fa353adea98 <rtl::Static<(anonymous namespace)::SwDLLInstance, (anonymous namespace)::theSwDLLInstance>::get()::instance+8>, __p=0x2b9b7e0) at /usr/include/c++/7/bits/unique_ptr.h:376
#13 0x00007fa35284f3a1 in comphelper::unique_disposing_ptr<SwDLL>::reset(SwDLL*) (this=0x7fa353adea90 <rtl::Static<(anonymous namespace)::SwDLLInstance, (anonymous namespace)::theSwDLLInstance>::get()::instance>, p=0x0) at /work/lo/master/include/comphelper/unique_disposing_ptr.hxx:42
#14 0x00007fa35284ec7e in comphelper::unique_disposing_solar_mutex_reset_ptr<SwDLL>::reset(SwDLL*) (this=0x7fa353adea90 <rtl::Static<(anonymous namespace)::SwDLLInstance, (anonymous namespace)::theSwDLLInstance>::get()::instance>, p=0x0) at /work/lo/master/include/comphelper/unique_disposing_ptr.hxx:171
#15 0x00007fa35284e5fa in comphelper::unique_disposing_solar_mutex_reset_ptr<SwDLL>::~unique_disposing_solar_mutex_reset_ptr() (this=0x7fa353adea90 <rtl::Static<(anonymous namespace)::SwDLLInstance, (anonymous namespace)::theSwDLLInstance>::get()::instance>, __in_chrg=<optimized out>) at /work/lo/master/include/comphelper/unique_disposing_ptr.hxx:177
#16 0x00007fa35284e460 in (anonymous namespace)::SwDLLInstance::~SwDLLInstance() (this=0x7fa353adea90 <rtl::Static<(anonymous namespace)::SwDLLInstance, (anonymous namespace)::theSwDLLInstance>::get()::instance>, __in_chrg=<optimized out>) at /work/lo/master/sw/source/uibase/app/swdll.cxx:57
#17 0x00007fa381647c68 in __run_exit_handlers () at /lib64/libc.so.6
#18 0x00007fa381647cba in  () at /lib64/libc.so.6
#19 0x00007fa38162d511 in __libc_start_main () at /lib64/libc.so.6
#20 0x000000000040a1ba in _start ()

actually it's not really a deadlock - the mutex being locked
is a global variable that has already been destroyed - usually
this only prints a warning like
"pthread_mutex_lock failed: Invalid argument"
but apparently sometimes the freed memory looks like a valid
mutex that is already locked.

this is a regression from:

commit a99707d2c4f65a6a5fe160ce2b614aca273f0d2d
Author:     Caolán McNamara <caolanm@redhat.com>
AuthorDate: Mon May 8 15:26:22 2017 +0100

    Resolves: rhbz#144437 make gnome-documents not crash the whole time
    
    accept that once initted that LibreOffice cannot be deinitted and reinited
    (without lots of work), but allow the main loop to quit and restart so LOKs
    thread can run and exit successfully, new LOK connections will restart the m
ain
    loop.
    
    The buckets of global state continues to be valid the whole time this way


... which turned framework::Desktop::terminate() into a no-op when
called from LOKit.

this is clearly the wrong solution to the problem - now there is no
way for a LibreOfficeKit client to actually destroy all the thousands
of global variables, so unless the client uses _exit(), they
will sometimes crash or deadlock during shutdown.

(i would not be opposed to requiring LOKit clients to use _exit(),
but that should be documented somewhere.)

really the problem is that in the LOKDocView the
"static void lok_doc_view_destroy (GtkWidget* widget)"
calls "priv->m_pOffice->pClass->destroy (priv->m_pOffice)"
- but this must be called only once per process, when
the process shuts down, not when just some view is destroyed.

because of this i'll disable the unit test on master now.