Application: kwin_x11 (5.9.4)
 (Compiled from sources)
Qt Version: 5.8.0
Frameworks Version: 5.33.0
Operating System: Linux 4.10.10-1-ck x86_64
Distribution (Platform): Archlinux Packages

-- Information about the crash:
- Unusual behavior I noticed:
Just after login via LightDM I've got this crash, resulting in KWin falling back to no-effects mode. Also, Latte-Dock was not able to autostart (though I think it's because of not having OpenGL compositing and stuff). If I go to systemsettings and re-enable OpenGL, everything works fine.
I think that may be related to Plasma 5 crashes with QT 5.8.0, as I've seen patches in Arch's repos with their name suggesting that something's wrong with "latest Plasma + QT 5.8" combo.
I have my KDE apps compiled via makepkg with -O2 and -{march,mtune}=native optimisation flags it matters.
This issue happens randomly, although I've encountered it a few times in the last four days.

The crash can be reproduced sometimes.

-- Backtrace:
Application: KWin (kwin_x11), signal: Segmentation fault
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[Current thread is 1 (Thread 0x7f55d9b83840 (LWP 947))]

Thread 11 (Thread 0x7f5587fff700 (LWP 1248)):
#0  0x00007f55d2779756 in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007f55d5b00234 in  () at /usr/lib/libQt5Script.so.5
#2  0x00007f55d5b00279 in  () at /usr/lib/libQt5Script.so.5
#3  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#4  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 10 (Thread 0x7f559da35700 (LWP 1174)):
#0  0x00007f55d2779756 in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007f55a362665c in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#2  0x00007f55a3626337 in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#3  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#4  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 9 (Thread 0x7f559e236700 (LWP 1173)):
#0  0x00007f55d2779756 in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007f55a362665c in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#2  0x00007f55a3626337 in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#3  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#4  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 8 (Thread 0x7f559ea37700 (LWP 1172)):
#0  0x00007f55d2779756 in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007f55a362665c in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#2  0x00007f55a3626337 in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#3  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#4  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 7 (Thread 0x7f559f238700 (LWP 1171)):
#0  0x00007f55d2779756 in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007f55a362665c in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#2  0x00007f55a3626337 in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#3  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#4  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 6 (Thread 0x7f559fc3e700 (LWP 1170)):
#0  0x00007f55d2779756 in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007f55a362665c in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#2  0x00007f55a3626337 in  () at /usr/lib/xorg/modules/dri/radeonsi_dri.so
#3  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#4  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 5 (Thread 0x7f55b61f8700 (LWP 1161)):
[KCrash Handler]
#6  0x00007f55d6b208bb in  () at /usr/lib/libQt5Core.so.5
#7  0x00007f55d6ab866f in QLockFile::tryLock(int) () at /usr/lib/libQt5Core.so.5
#8  0x00007f55d893bf09 in  () at /usr/lib/libKF5ConfigCore.so.5
#9  0x00007f55d89220e8 in KConfig::sync() () at /usr/lib/libKF5ConfigCore.so.5
#10 0x00007f55bd37b52a in  () at /usr/lib/qt/plugins/org.kde.kwin.platforms/KWinX11Platform.so
#11 0x00007f55d6bc450c in QMetaObject::activate(QObject*, int, int, void**) () at /usr/lib/libQt5Core.so.5
#12 0x00007f55d6bd173c in QTimer::timerEvent(QTimerEvent*) () at /usr/lib/libQt5Core.so.5
#13 0x00007f55d6bc5103 in QObject::event(QEvent*) () at /usr/lib/libQt5Core.so.5
#14 0x00007f55d78ab5ac in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#15 0x00007f55d78b335c in QApplication::notify(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#16 0x00007f55d6b94d80 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/libQt5Core.so.5
#17 0x00007f55d6bedd90 in QTimerInfoList::activateTimers() () at /usr/lib/libQt5Core.so.5
#18 0x00007f55d6bebaec in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#19 0x00007f55d6b92b23 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#20 0x00007f55d699a9d6 in QThread::exec() () at /usr/lib/libQt5Core.so.5
#21 0x00007f55d699fcc4 in  () at /usr/lib/libQt5Core.so.5
#22 0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#23 0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 4 (Thread 0x7f55b7289700 (LWP 1133)):
#0  0x00007f55d95da76b in ppoll () at /usr/lib/libc.so.6
#1  0x00007f55d6bea043 in qt_safe_poll(pollfd*, unsigned long, timespec const*) () at /usr/lib/libQt5Core.so.5
#2  0x00007f55d6beb87b in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#3  0x00007f55d6b92b23 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#4  0x00007f55d699a9d6 in QThread::exec() () at /usr/lib/libQt5Core.so.5
#5  0x00007f55d148b025 in  () at /usr/lib/libQt5Qml.so.5
#6  0x00007f55d699fcc4 in  () at /usr/lib/libQt5Core.so.5
#7  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#8  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 3 (Thread 0x7f55bdd9f700 (LWP 1043)):
#0  0x00007f55d95da76b in ppoll () at /usr/lib/libc.so.6
#1  0x00007f55d6bea043 in qt_safe_poll(pollfd*, unsigned long, timespec const*) () at /usr/lib/libQt5Core.so.5
#2  0x00007f55d6beb87b in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#3  0x00007f55d6b92b23 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#4  0x00007f55d699a9d6 in QThread::exec() () at /usr/lib/libQt5Core.so.5
#5  0x00007f55d062f834 in  () at /usr/lib/libQt5DBus.so.5
#6  0x00007f55d699fcc4 in  () at /usr/lib/libQt5Core.so.5
#7  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#8  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 2 (Thread 0x7f55bfef6700 (LWP 1022)):
#0  0x00007f55d95da67d in poll () at /usr/lib/libc.so.6
#1  0x00007f55d86e78df in  () at /usr/lib/libxcb.so.1
#2  0x00007f55d86e98a9 in xcb_wait_for_event () at /usr/lib/libxcb.so.1
#3  0x00007f55c0fd208a in  () at /usr/lib/libQt5XcbQpa.so.5
#4  0x00007f55d699fcc4 in  () at /usr/lib/libQt5Core.so.5
#5  0x00007f55d27732e7 in start_thread () at /usr/lib/libpthread.so.0
#6  0x00007f55d95e454f in clone () at /usr/lib/libc.so.6

Thread 1 (Thread 0x7f55d9b83840 (LWP 947)):
#0  0x00007f55d2779756 in pthread_cond_wait@@GLIBC_2.3.2 () at /usr/lib/libpthread.so.0
#1  0x00007f55d69a0c9c in QWaitCondition::wait(QMutex*, unsigned long) () at /usr/lib/libQt5Core.so.5
#2  0x00007f55d699f7f7 in QThread::wait(unsigned long) () at /usr/lib/libQt5Core.so.5
#3  0x00007f55bd37b201 in KWin::X11StandalonePlatform::createOpenGLSafePoint(KWin::Platform::OpenGLSafePoint) () at /usr/lib/qt/plugins/org.kde.kwin.platforms/KWinX11Platform.so
#4  0x00007f55d913eb44 in KWin::Compositor::performCompositing() () at /usr/lib/libkwin.so.5
#5  0x00007f55d6bc5103 in QObject::event(QEvent*) () at /usr/lib/libQt5Core.so.5
#6  0x00007f55d78ab5ac in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#7  0x00007f55d78b335c in QApplication::notify(QObject*, QEvent*) () at /usr/lib/libQt5Widgets.so.5
#8  0x00007f55d6b94d80 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/libQt5Core.so.5
#9  0x00007f55d6bedd90 in QTimerInfoList::activateTimers() () at /usr/lib/libQt5Core.so.5
#10 0x00007f55d6bebaec in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#11 0x00007f55c103783d in  () at /usr/lib/libQt5XcbQpa.so.5
#12 0x00007f55d6b92b23 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#13 0x00007f55d6b9bac7 in QCoreApplication::exec() () at /usr/lib/libQt5Core.so.5
#14 0x00007f55d98a4c38 in kdemain () at /usr/lib/libkdeinit5_kwin_x11.so
#15 0x00007f55d9518511 in __libc_start_main () at /usr/lib/libc.so.6
#16 0x0000563317dee80a in _start ()

Reported using DrKonqi