Application: kwin_x11 (5.3.90)
 (Compiled from sources)
Qt Version: 5.4.1
Operating System: Linux 4.0.1-040001-generic x86_64
Distribution: Ubuntu 15.04

-- Information about the crash:
- What I was doing when the application crashed:
I pressed Ctrl+O in QtCreator to bring up the Open File dialog. For some reason it doesn't always show up (I think there was/is a bug in QDialog that was fixed and broke again a couple of times), when I press Escape a couple of times to quit the event loop spawned by the dialog, KWin usually crashes.

The crash can be reproduced sometimes.

-- Backtrace:
Application: KWin (kwin_x11), signal: Segmentation fault
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[Current thread is 1 (Thread 0x7ff293278800 (LWP 26015))]

Thread 4 (Thread 0x7ff2730dc700 (LWP 26018)):
#0  0x00007ff292d5a743 in select () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007ff291217101 in qt_safe_select(int, fd_set*, fd_set*, fd_set*, timespec const*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#2  0x00007ff291218cd2 in QEventDispatcherUNIXPrivate::doSelect(QFlags<QEventLoop::ProcessEventsFlag>, timespec*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007ff291219275 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007ff2911c03e2 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007ff290f7fb44 in QThread::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#6  0x00007ff28afdff65 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#7  0x00007ff290f84b0e in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#8  0x00007ff2924e16aa in start_thread (arg=0x7ff2730dc700) at pthread_create.c:333
#9  0x00007ff292d63eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 3 (Thread 0x7ff267fff700 (LWP 26020)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x00007ff28fd0a644 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Script.so.5
#2  0x00007ff28fd0a689 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Script.so.5
#3  0x00007ff2924e16aa in start_thread (arg=0x7ff267fff700) at pthread_create.c:333
#4  0x00007ff292d63eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 2 (Thread 0x7ff2791c9700 (LWP 27688)):
#0  0x00007ff292d5a743 in select () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007ff291217101 in qt_safe_select(int, fd_set*, fd_set*, fd_set*, timespec const*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#2  0x00007ff291218cd2 in QEventDispatcherUNIXPrivate::doSelect(QFlags<QEventLoop::ProcessEventsFlag>, timespec*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007ff291219275 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007ff2911c03e2 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007ff290f7fb44 in QThread::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#6  0x00007ff28afdff65 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#7  0x00007ff290f84b0e in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#8  0x00007ff2924e16aa in start_thread (arg=0x7ff2791c9700) at pthread_create.c:333
#9  0x00007ff292d63eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 1 (Thread 0x7ff293278800 (LWP 26015)):
[KCrash Handler]
#6  0x0000000003972fb0 in ?? ()
#7  0x00007ff292899919 in KWin::EffectsHandlerImpl::EffectsHandlerImpl(KWin::Compositor*, KWin::Scene*)::{lambda(KWin::AbstractClient*, int)#5}::operator()(KWin::AbstractClient*, int) const () at /home/kaiuwe/Projekte/kf5/src/kde/workspace/kwin/effects.cpp:238
#8  0x00007ff2928a48a2 in QtPrivate::FunctorCall<QtPrivate::IndexesList<0, 1>, QtPrivate::List<KWin::AbstractClient*, int>, void, KWin::EffectsHandlerImpl::EffectsHandlerImpl(KWin::Compositor*, KWin::Scene*)::<lambda(KWin::AbstractClient*, int)> >::call(KWin::EffectsHandlerImpl::<lambda(KWin::AbstractClient*, int)>, void **) (f=..., arg=0x7ffcf1251120) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs_impl.h:494
#9  0x00007ff2928a457d in QtPrivate::Functor<KWin::EffectsHandlerImpl::EffectsHandlerImpl(KWin::Compositor*, KWin::Scene*)::<lambda(KWin::AbstractClient*, int)>, 2>::call<QtPrivate::List<KWin::AbstractClient*, int>, void>(KWin::EffectsHandlerImpl::<lambda(KWin::AbstractClient*, int)> &, void *, void **) (f=..., arg=0x7ffcf1251120) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs_impl.h:551
#10 0x00007ff2928a3bc7 in QtPrivate::QFunctorSlotObject<KWin::EffectsHandlerImpl::EffectsHandlerImpl(KWin::Compositor*, KWin::Scene*)::<lambda(KWin::AbstractClient*, int)>, 2, QtPrivate::List<KWin::AbstractClient*, int>, void>::impl(int, QtPrivate::QSlotObjectBase *, QObject *, void **, bool *) (which=1, this_=0x31105f0, r=0x3109360, a=0x7ffcf1251120, ret=0x0) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject_impl.h:192
#11 0x00007ff2911f335a in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#12 0x00007ff2929606ad in KWin::Workspace::desktopPresenceChanged (this=0x2311980, _t1=0x3ae7f80, _t2=0) at /home/kaiuwe/Projekte/kf5/build/kde/workspace/kwin/moc_workspace.cpp:658
#13 0x00007ff29279139a in QtPrivate::FunctorCall<QtPrivate::IndexesList<0, 1>, QtPrivate::List<KWin::AbstractClient*, int>, void, void (KWin::Workspace::*)(KWin::AbstractClient*, int)>::call (f=(void (KWin::Workspace::*)(KWin::Workspace * const, KWin::AbstractClient *, int)) 0x7ff292960644 <KWin::Workspace::desktopPresenceChanged(KWin::AbstractClient*, int)>, o=0x2311980, arg=0x39842c0) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs_impl.h:500
#14 0x00007ff29278f95e in QtPrivate::FunctionPointer<void (KWin::Workspace::*)(KWin::AbstractClient*, int)>::call<QtPrivate::List<KWin::AbstractClient*, int>, void> (f=(void (KWin::Workspace::*)(KWin::Workspace * const, KWin::AbstractClient *, int)) 0x7ff292960644 <KWin::Workspace::desktopPresenceChanged(KWin::AbstractClient*, int)>, o=0x2311980, arg=0x39842c0) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobjectdefs_impl.h:519
#15 0x00007ff29278d10f in QtPrivate::QSlotObject<void (KWin::Workspace::*)(KWin::AbstractClient*, int), QtPrivate::List<KWin::AbstractClient*, int>, void>::impl (which=1, this_=0x32c0680, r=0x2311980, a=0x39842c0, ret=0x0) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject_impl.h:143
#16 0x00007ff2911f473a in QObject::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#17 0x00007ff291accb2c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#18 0x00007ff291ad2000 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#19 0x00007ff2927d800f in KWin::Application::notify (this=0x7ffcf1251750, o=0x2311980, e=0x32bfc80) at /home/kaiuwe/Projekte/kf5/src/kde/workspace/kwin/main.cpp:241
#20 0x00007ff2911c2c2b in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#21 0x00007ff2911c4c9b in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#22 0x00007ff291219112 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#23 0x00007ff27c94d96d in ?? () from /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so
#24 0x00007ff2911c03e2 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#25 0x00007ff2911c802c in QCoreApplication::exec() () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#26 0x00007ff29302c461 in kdemain (argc=2, argv=0x7ffcf12518b8) at /home/kaiuwe/Projekte/kf5/src/kde/workspace/kwin/main_x11.cpp:302
#27 0x00000000004008d8 in main (argc=2, argv=0x7ffcf12518b8) at /home/kaiuwe/Projekte/kf5/build/kde/workspace/kwin/kwin_x11_dummy.cpp:3

Reported using DrKonqi