Application: kwin_x11 (5.12.6)

Qt Version: 5.9.5
Frameworks Version: 5.44.0
Operating System: Linux 4.15.0-36-generic x86_64
Distribution: Ubuntu 18.04.1 LTS

-- Information about the crash:
- What I was doing when the application crashed:
The title mentions all, I started Firefox and then some sort of freeze occurs.

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 0x7f4d82b3ecc0 (LWP 1717))]

Thread 6 (Thread 0x7f4d4e839700 (LWP 2242)):
#0  0x00007ffd2dca2979 in  ()
#1  0x00007ffd2dca2c30 in clock_gettime ()
#2  0x00007f4d824baea6 in __GI___clock_gettime (clock_id=1, tp=0x7f4d4e838b90) at ../sysdeps/unix/clock_gettime.c:115
#3  0x00007f4d7f8a4221 in  () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007f4d7f8a2a59 in QTimerInfoList::updateCurrentTime() () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007f4d7f8a3035 in QTimerInfoList::timerWait(timespec&) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#6  0x00007f4d7f8a1fe4 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#7  0x00007f4d7f8499ea in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#8  0x00007f4d7f66822a in QThread::exec() () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#9  0x00007f4d79ff16f5 in  () at /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#10 0x00007f4d7f66d16d in  () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#11 0x00007f4d7b5056db in start_thread (arg=0x7f4d4e839700) at pthread_create.c:463
#12 0x00007f4d824ab88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 5 (Thread 0x7f4d4e038700 (LWP 1806)):
#0  0x00007f4d7b50b9f3 in futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x7f4d7eaa2fb8) at ../sysdeps/unix/sysv/linux/futex-internal.h:88
#1  0x00007f4d7b50b9f3 in __pthread_cond_wait_common (abstime=0x0, mutex=0x7f4d7eaa2f68, cond=0x7f4d7eaa2f90) at pthread_cond_wait.c:502
#2  0x00007f4d7b50b9f3 in __pthread_cond_wait (cond=0x7f4d7eaa2f90, mutex=0x7f4d7eaa2f68) at pthread_cond_wait.c:655
#3  0x00007f4d7e7ac5f4 in  () at /usr/lib/x86_64-linux-gnu/libQt5Script.so.5
#4  0x00007f4d7e7ac639 in  () at /usr/lib/x86_64-linux-gnu/libQt5Script.so.5
#5  0x00007f4d7b5056db in start_thread (arg=0x7f4d4e038700) at pthread_create.c:463
#6  0x00007f4d824ab88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 4 (Thread 0x7f4d5bfff700 (LWP 1777)):
#0  0x00007f4d8249ecf6 in __GI_ppoll (fds=0x7f4d50000d28, nfds=1, timeout=<optimized out>, sigmask=0x0) at ../sysdeps/unix/sysv/linux/ppoll.c:39
#1  0x00007f4d7f8a05c1 in qt_safe_poll(pollfd*, unsigned long, timespec const*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#2  0x00007f4d7f8a1cde in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007f4d7f8499ea in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007f4d7f66822a in QThread::exec() () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007f4d79ff16f5 in  () at /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#6  0x00007f4d7f66d16d in  () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#7  0x00007f4d7b5056db in start_thread (arg=0x7f4d5bfff700) at pthread_create.c:463
#8  0x00007f4d824ab88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 3 (Thread 0x7f4d629cf700 (LWP 1731)):
#0  0x00007f4d7f856580 in QMetaObjectPrivate::signalOffset(QMetaObject const*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#1  0x00007f4d7f87ac74 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#2  0x00007f4d7f8a1ea0 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007f4d7f8499ea in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007f4d7f66822a in QThread::exec() () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007f4d78ecad45 in  () at /usr/lib/x86_64-linux-gnu/libQt5DBus.so.5
#6  0x00007f4d7f66d16d in  () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#7  0x00007f4d7b5056db in start_thread (arg=0x7f4d629cf700) at pthread_create.c:463
#8  0x00007f4d824ab88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 2 (Thread 0x7f4d691be700 (LWP 1718)):
#0  0x00007f4d8249ebf9 in __GI___poll (fds=0x7f4d691bdc68, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00007f4d813a8747 in  () at /usr/lib/x86_64-linux-gnu/libxcb.so.1
#2  0x00007f4d813aa36a in xcb_wait_for_event () at /usr/lib/x86_64-linux-gnu/libxcb.so.1
#3  0x00007f4d6a09d2a9 in  () at /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#4  0x00007f4d7f66d16d in  () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007f4d7b5056db in start_thread (arg=0x7f4d691be700) at pthread_create.c:463
#6  0x00007f4d824ab88f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 1 (Thread 0x7f4d82b3ecc0 (LWP 1717)):
[KCrash Handler]
#6  0x00007f4d81fa7723 in  () at /usr/lib/x86_64-linux-gnu/libkwin.so.5
#7  0x00007f4d81fa6386 in KWin::Workspace::workspaceEvent(xcb_generic_event_t*) () at /usr/lib/x86_64-linux-gnu/libkwin.so.5
#8  0x00007f4d7f84858f in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#9  0x00007f4d6a09e820 in QXcbConnection::handleXcbEvent(xcb_generic_event_t*) () at /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#10 0x00007f4d6a09f4ac in QXcbConnection::processXcbEvents() () at /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#11 0x00007f4d7f87b122 in QObject::event(QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#12 0x00007f4d805c982c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#13 0x00007f4d805d10f4 in QApplication::notify(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5
#14 0x00007f4d7f84b9a8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#15 0x00007f4d7f84e11d in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#16 0x00007f4d7f8a1af4 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#17 0x00007f4d6a1005cd in  () at /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#18 0x00007f4d7f8499ea in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#19 0x00007f4d7f852a84 in QCoreApplication::exec() () at /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#20 0x00007f4d82783dbb in kdemain () at /usr/lib/x86_64-linux-gnu/libkdeinit5_kwin_x11.so
#21 0x00007f4d823abb97 in __libc_start_main (main=0x5610d975c730, argc=3, argv=0x7ffd2dc95c98, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffd2dc95c88) at ../csu/libc-start.c:310
#22 0x00005610d975c76a in _start ()

Reported using DrKonqi