> Application: kwin_x11 (5.8.9)

Hmm, this is quite old KDE Plasma version. Can you reproduce the crash in more modern versions?

Apparently the crash happens somewhere in libxcb, though it would be great to have a backtrace with debug symbols.

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This VM was working without incident when I stopped using it after creating an updated guest in Kubuntu 18.04. Occasionally I still start the old machine to extract some data. Generally I apply any updates which are pending on the old 16.04 machine. Since the initial report, I get a kwin error every time it starts. No such problems occur on the replacement 18.04 VM.

This is today's backtrace:
Application: KWin (kwin_x11), signal: Aborted
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
[Current thread is 1 (Thread 0x7fb3b9b1a940 (LWP 2690))]

Thread 5 (Thread 0x7fb38f5ef700 (LWP 2791)):
[KCrash Handler]
#6  0x00007fb3b9549428 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
#7  0x00007fb3b954b02a in __GI_abort () at abort.c:89
#8  0x00007fb3b7241f41 in QMessageLogger::fatal(char const*, ...) const () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#9  0x00007fb39e58d1b4 in ?? () from /usr/lib/x86_64-linux-gnu/qt5/plugins/org.kde.kwin.platforms/KWinX11Platform.so
#10 0x00007fb3b745bc24 in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#11 0x00007fb3b74680b8 in QTimer::timerEvent(QTimerEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#12 0x00007fb3b745c6d3 in QObject::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#13 0x00007fb3b7d64afc in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#14 0x00007fb3b7d6a036 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#15 0x00007fb3b742f2a8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#16 0x00007fb3b748324e in QTimerInfoList::activateTimers() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#17 0x00007fb3b7481b04 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#18 0x00007fb3b742cffa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#19 0x00007fb3b72559e4 in QThread::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#20 0x00007fb3b725a808 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#21 0x00007fb3b32cb6ba in start_thread (arg=0x7fb38f5ef700) at pthread_create.c:333
#22 0x00007fb3b961b41d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 4 (Thread 0x7fb39d1f0700 (LWP 2780)):
#0  0x00007fb3b7252949 in QMutex::lock() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#1  0x00007fb3b7430f5c in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#2  0x00007fb3b7481a02 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007fb3b742cffa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007fb3b72559e4 in QThread::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007fb3b24256b5 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#6  0x00007fb3b725a808 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#7  0x00007fb3b32cb6ba in start_thread (arg=0x7fb39d1f0700) at pthread_create.c:333
#8  0x00007fb3b961b41d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 3 (Thread 0x7fb39efac700 (LWP 2750)):
#0  0x00007fb3b96115d3 in select () at ../sysdeps/unix/syscall-template.S:84
#1  0x00007fb3b747fbcf in qt_safe_select(int, fd_set*, fd_set*, fd_set*, timespec const*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#2  0x00007fb3b748160e in QEventDispatcherUNIXPrivate::doSelect(QFlags<QEventLoop::ProcessEventsFlag>, timespec*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007fb3b7481b22 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007fb3b742cffa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007fb3b72559e4 in QThread::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#6  0x00007fb3b9c42515 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5DBus.so.5
#7  0x00007fb3b725a808 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#8  0x00007fb3b32cb6ba in start_thread (arg=0x7fb39efac700) at pthread_create.c:333
#9  0x00007fb3b961b41d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 2 (Thread 0x7fb3a0aa4700 (LWP 2734)):
#0  0x00007fb3b960f74d in poll () at ../sysdeps/unix/syscall-template.S:84
#1  0x00007fb3b8774c62 in ?? () from /usr/lib/x86_64-linux-gnu/libxcb.so.1
#2  0x00007fb3b87768d7 in xcb_wait_for_event () from /usr/lib/x86_64-linux-gnu/libxcb.so.1
#3  0x00007fb3a1751d29 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#4  0x00007fb3b725a808 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007fb3b32cb6ba in start_thread (arg=0x7fb3a0aa4700) at pthread_create.c:333
#6  0x00007fb3b961b41d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 1 (Thread 0x7fb3b9b1a940 (LWP 2690)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x00007fb3b8774eb9 in ?? () from /usr/lib/x86_64-linux-gnu/libxcb.so.1
#2  0x00007fb3b8776617 in ?? () from /usr/lib/x86_64-linux-gnu/libxcb.so.1
#3  0x00007fb3b8776721 in xcb_wait_for_reply () from /usr/lib/x86_64-linux-gnu/libxcb.so.1
#4  0x00007fb3b914b3df in ?? () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#5  0x00007fb3b914d049 in ?? () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#6  0x00007fb3b914dca1 in ?? () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#7  0x00007fb3b9198b85 in KWin::Toplevel::getShadow() () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#8  0x00007fb3b919eed8 in KWin::Scene::windowAdded(KWin::Toplevel*) () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#9  0x00007fb3b9191407 in KWin::Toplevel::setupCompositing() () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#10 0x00007fb3b91937bd in KWin::Compositor::startupWithWorkspace() () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#11 0x00007fb3b9194253 in KWin::Compositor::slotCompositingOptionsInitialized() () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#12 0x00007fb3b9194792 in KWin::Compositor::setup() () from /usr/lib/x86_64-linux-gnu/libkwin.so.5
#13 0x00007fb3b745c719 in QObject::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#14 0x00007fb3b7d64afc in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#15 0x00007fb3b7d6a036 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#16 0x00007fb3b742f2a8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#17 0x00007fb3b743116a in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#18 0x00007fb3b7481a02 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#19 0x00007fb3a17c58fd in ?? () from /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#20 0x00007fb3b742cffa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#21 0x00007fb3b74356bc in QCoreApplication::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#22 0x00007fb3b98e7226 in kdemain () from /usr/lib/x86_64-linux-gnu/libkdeinit5_kwin_x11.so
#23 0x00007fb3b9534830 in __libc_start_main (main=0x400730, argc=3, argv=0x7ffcc7ad9848, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffcc7ad9838) at ../csu/libc-start.c:291
#24 0x0000000000400769 in _start ()

Update: Today I applied 52 updates to the old 16.04 VM. After doing so, the system booted normally and without any KWin errors.

Distribution issue.