Application: kwin_x11 (5.2.2)
 (Compiled from sources)
Qt Version: 5.4.1
Operating System: Linux 3.19.0-21-generic x86_64
Distribution: Ubuntu 15.04

-- Information about the crash:
- What I was doing when the application crashed: at the terminal removing google-chrome. but I think it happens whatever I may be doing, after coming back from the welcome screen, without having logout (it goes to the welcome screen automatically if unused).

- Unusual behavior I noticed: it crashes constantly everytime the computer automatically goes to the welcome screen (not logout). the windows don't display correctly. either kubuntu asks me to restart kwin and then is fine or, I have to logout and login since I didn't know what was causing the problem.

-- 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 0x7f20874ce800 (LWP 26418))]

Thread 6 (Thread 0x7f206abab700 (LWP 26425)):
#0  0x00007ffd1c3dbcee in clock_gettime ()
#1  0x00007f2086fb438d in __GI___clock_gettime (clock_id=<optimized out>, tp=<optimized out>) at ../sysdeps/unix/clock_gettime.c:115
#2  0x00007f2085609cb6 in qt_clock_gettime (ts=0x7f206abaac50, clock=<optimized out>) at tools/qelapsedtimer_unix.cpp:105
#3  do_gettime (frac=<synthetic pointer>, sec=<synthetic pointer>) at tools/qelapsedtimer_unix.cpp:161
#4  qt_gettime () at tools/qelapsedtimer_unix.cpp:170
#5  0x00007f20857e8639 in QTimerInfoList::updateCurrentTime (this=this@entry=0x7f205c001118) at kernel/qtimerinfo_unix.cpp:84
#6  0x00007f20857e8ba5 in QTimerInfoList::timerWait (this=this@entry=0x7f205c001118, tm=...) at kernel/qtimerinfo_unix.cpp:379
#7  0x00007f20857e8222 in QEventDispatcherUNIX::processEvents (this=0x7f205c0008c0, flags=...) at kernel/qeventdispatcher_unix.cpp:594
#8  0x00007f208578f3e2 in QEventLoop::exec (this=this@entry=0x7f206abaada0, flags=..., flags@entry=...) at kernel/qeventloop.cpp:204
#9  0x00007f208554eb44 in QThread::exec (this=<optimized out>) at thread/qthread.cpp:503
#10 0x00007f207f401f65 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#11 0x00007f2085553b0e in QThreadPrivate::start (arg=0x11c1750) at thread/qthread_unix.cpp:337
#12 0x00007f207e5ce6aa in start_thread (arg=0x7f206abab700) at pthread_create.c:333
#13 0x00007f2086fa5eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 5 (Thread 0x7f2068ce3700 (LWP 26426)):
#0  0x00007f2086f9c0b7 in ioctl () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007f20699a9919 in uki_firegl_MicroSleep () from /usr/lib/libatiuki.so.1
#2  0x00007f20636f1920 in ?? () from /usr/lib/dri/fglrx_dri.so
#3  0x00007f2062e82d72 in ?? () from /usr/lib/dri/fglrx_dri.so
#4  0x00007f2062e82dc5 in ?? () from /usr/lib/dri/fglrx_dri.so
#5  0x00007f207e5ce6aa in start_thread (arg=0x7f2068ce3700) at pthread_create.c:333
#6  0x00007f2086fa5eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 4 (Thread 0x7f2057ead700 (LWP 26428)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x00007f2084358644 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Script.so.5
#2  0x00007f2084358689 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Script.so.5
#3  0x00007f207e5ce6aa in start_thread (arg=0x7f2057ead700) at pthread_create.c:333
#4  0x00007f2086fa5eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 3 (Thread 0x7f20608d4700 (LWP 26749)):
#0  0x00007f2086f9c743 in select () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007f20857e6101 in qt_safe_select (nfds=13, fdread=fdread@entry=0x7f2050000a78, fdwrite=fdwrite@entry=0x7f2050000d08, fdexcept=fdexcept@entry=0x7f2050000f98, orig_timeout=orig_timeout@entry=0x0) at kernel/qcore_unix.cpp:75
#2  0x00007f20857e7cd2 in select (timeout=0x0, exceptfds=0x7f2050000f98, writefds=0x7f2050000d08, readfds=0x7f2050000a78, nfds=<optimized out>, this=0x7f20500008c0) at kernel/qeventdispatcher_unix.cpp:320
#3  QEventDispatcherUNIXPrivate::doSelect (this=this@entry=0x7f20500008e0, flags=..., flags@entry=..., timeout=timeout@entry=0x0) at kernel/qeventdispatcher_unix.cpp:196
#4  0x00007f20857e8275 in QEventDispatcherUNIX::processEvents (this=0x7f20500008c0, flags=...) at kernel/qeventdispatcher_unix.cpp:607
#5  0x00007f208578f3e2 in QEventLoop::exec (this=this@entry=0x7f20608d3da0, flags=..., flags@entry=...) at kernel/qeventloop.cpp:204
#6  0x00007f208554eb44 in QThread::exec (this=<optimized out>) at thread/qthread.cpp:503
#7  0x00007f207f401f65 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#8  0x00007f2085553b0e in QThreadPrivate::start (arg=0x19d2930) at thread/qthread_unix.cpp:337
#9  0x00007f207e5ce6aa in start_thread (arg=0x7f20608d4700) at pthread_create.c:333
#10 0x00007f2086fa5eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 2 (Thread 0x7f206b5ef700 (LWP 26750)):
#0  pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1  0x00007f2085554c6b in wait (time=18446744073709551615, this=0x1d52990) at thread/qwaitcondition_unix.cpp:128
#2  QWaitCondition::wait (this=<optimized out>, mutex=0x1b2ea20, time=18446744073709551615) at thread/qwaitcondition_unix.cpp:200
#3  0x00007f20845dffab in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Quick.so.5
#4  0x00007f20845e03a0 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Quick.so.5
#5  0x00007f2085553b0e in QThreadPrivate::start (arg=0x1b2e9a0) at thread/qthread_unix.cpp:337
#6  0x00007f207e5ce6aa in start_thread (arg=0x7f206b5ef700) at pthread_create.c:333
#7  0x00007f2086fa5eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 1 (Thread 0x7f20874ce800 (LWP 26418)):
[KCrash Handler]
#6  0x00007f206278556a in ?? () from /usr/lib/dri/fglrx_dri.so
#7  0x00007f206258fb47 in ?? () from /usr/lib/dri/fglrx_dri.so
#8  0x00007f206258f3da in ?? () from /usr/lib/dri/fglrx_dri.so
#9  0x00007f2062916d80 in ?? () from /usr/lib/dri/fglrx_dri.so
#10 0x00007f20629173c9 in ?? () from /usr/lib/dri/fglrx_dri.so
#11 0x00007f2061cb6c2c in ?? () from /usr/lib/dri/fglrx_dri.so
#12 0x00007f2061b8c383 in ?? () from /usr/lib/dri/fglrx_dri.so
#13 0x00007f2061ef7d66 in ?? () from /usr/lib/dri/fglrx_dri.so
#14 0x00007f207f851371 in KWin::GLVertexBuffer::draw (this=this@entry=0x17c0ea0, region=..., primitiveMode=primitiveMode@entry=4, first=first@entry=6, count=count@entry=6, hardwareClipping=hardwareClipping@entry=false) at ../../libkwineffects/kwinglutils.cpp:2393
#15 0x00007f207f85180e in KWin::GLVertexBuffer::draw (this=0x17c0ea0, primitiveMode=4, first=6, count=6) at ../../libkwineffects/kwinglutils.cpp:2362
#16 0x00007f2084882688 in KWin::BlurEffect::doCachedBlur (this=0x18813d0, w=0x43, region=..., opacity=9.14767638e-41) at ../../effects/blur/blur.cpp:644
#17 0x00007f20848834e1 in KWin::BlurEffect::drawWindow (this=this@entry=0x18813d0, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../../effects/blur/blur.cpp:407
#18 0x00007f2086b850d1 in KWin::EffectsHandlerImpl::drawWindow (this=0x18570c0, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../effects.cpp:470
#19 0x00007f2086b4e841 in KWin::Scene::finalPaintWindow (this=<optimized out>, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../scene.cpp:605
#20 0x00007f2086b84f7a in KWin::EffectsHandlerImpl::paintWindow (this=0x18570c0, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../effects.cpp:436
#21 0x00007f2084d5f651 in KWin::Effect::paintWindow (this=this@entry=0x18f64b0, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../../libkwineffects/kwineffects.cpp:550
#22 0x00007f2086b84f21 in KWin::EffectsHandlerImpl::paintWindow (this=0x18570c0, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../effects.cpp:433
#23 0x00007f2084d5f651 in KWin::Effect::paintWindow (this=this@entry=0x1881250, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../../libkwineffects/kwineffects.cpp:550
#24 0x00007f2086b84f21 in KWin::EffectsHandlerImpl::paintWindow (this=0x18570c0, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../effects.cpp:433
#25 0x00007f2084d5f651 in KWin::Effect::paintWindow (this=this@entry=0x18813d0, w=w@entry=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../../libkwineffects/kwineffects.cpp:550
#26 0x00007f2086b84f21 in KWin::EffectsHandlerImpl::paintWindow (this=0x18570c0, w=0x185f5a0, mask=mask@entry=10, region=..., data=...) at ../effects.cpp:433
#27 0x00007f2086b52ee8 in KWin::Scene::paintWindow (this=this@entry=0x17d0710, w=0x184cff0, mask=10, region=..., quads=...) at ../scene.cpp:477
#28 0x00007f2086b50c0e in KWin::Scene::paintSimpleScreen (this=this@entry=0x17d0710, orig_mask=orig_mask@entry=8, region=...) at ../scene.cpp:380
#29 0x00007f2086b61513 in KWin::SceneOpenGL2::paintSimpleScreen (this=this@entry=0x17d0710, mask=mask@entry=8, region=...) at ../scene_opengl.cpp:1005
#30 0x00007f2086b4e205 in KWin::Scene::finalPaintScreen (this=0x17d0710, mask=mask@entry=8, region=..., data=...) at ../scene.cpp:199
#31 0x00007f2086b84cff in KWin::EffectsHandlerImpl::paintScreen (this=0x18570c0, mask=mask@entry=8, region=..., data=...) at ../effects.cpp:393
#32 0x00007f20848fce27 in KWin::ScreenEdgeEffect::paintScreen (this=this@entry=0x18f64b0, mask=mask@entry=8, region=..., data=...) at ../../effects/screenedge/screenedgeeffect.cpp:81
#33 0x00007f2086b84cad in KWin::EffectsHandlerImpl::paintScreen (this=0x18570c0, mask=mask@entry=8, region=..., data=...) at ../effects.cpp:390
#34 0x00007f2084d5f57f in KWin::Effect::paintScreen (this=this@entry=0x1881250, mask=mask@entry=8, region=..., data=...) at ../../libkwineffects/kwineffects.cpp:535
#35 0x00007f2086b84cad in KWin::EffectsHandlerImpl::paintScreen (this=0x18570c0, mask=mask@entry=8, region=..., data=...) at ../effects.cpp:390
#36 0x00007f2084d5f57f in KWin::Effect::paintScreen (this=this@entry=0x18813d0, mask=mask@entry=8, region=..., data=...) at ../../libkwineffects/kwineffects.cpp:535
#37 0x00007f2086b84cad in KWin::EffectsHandlerImpl::paintScreen (this=0x18570c0, mask=8, region=..., data=...) at ../effects.cpp:390
#38 0x00007f2086b4de6a in KWin::Scene::paintScreen (this=this@entry=0x17d0710, mask=mask@entry=0x7ffd1c34b2ec, damage=..., repaint=..., updateRegion=updateRegion@entry=0x7ffd1c34b300, validRegion=validRegion@entry=0x7ffd1c34b310) at ../scene.cpp:149
#39 0x00007f2086b67da7 in KWin::SceneOpenGL::paint (this=0x17d0710, damage=..., toplevels=...) at ../scene_opengl.cpp:651
#40 0x00007f2086b47973 in KWin::Compositor::performCompositing (this=0xf47fb0) at ../composite.cpp:658
#41 0x00007f20857c36f3 in QObject::event (this=0xf47fb0, e=<optimized out>) at kernel/qobject.cpp:1267
#42 0x00007f208609bb2c in QApplicationPrivate::notify_helper (this=0xe4f790, receiver=0xf47fb0, e=0x7ffd1c34b720) at kernel/qapplication.cpp:3720
#43 0x00007f20860a1000 in QApplication::notify (this=0x7ffd1c34b960, receiver=0xf47fb0, e=0x7ffd1c34b720) at kernel/qapplication.cpp:3503
#44 0x00007f2085791c2b in QCoreApplication::notifyInternal (this=0x7ffd1c34b960, receiver=0xf47fb0, event=event@entry=0x7ffd1c34b720) at kernel/qcoreapplication.cpp:935
#45 0x00007f20857e9ae5 in sendEvent (event=0x7ffd1c34b720, receiver=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:228
#46 QTimerInfoList::activateTimers (this=0xe853a8) at kernel/qtimerinfo_unix.cpp:635
#47 0x00007f20857e76a0 in QEventDispatcherUNIX::activateTimers (this=this@entry=0xe83620) at kernel/qeventdispatcher_unix.cpp:549
#48 0x00007f20857e8243 in QEventDispatcherUNIX::processEvents (this=0xe83620, flags=flags@entry=...) at kernel/qeventdispatcher_unix.cpp:611
#49 0x00007f20736cf96d in QUnixEventDispatcherQPA::processEvents (this=<optimized out>, flags=...) at eventdispatchers/qunixeventdispatcher.cpp:62
#50 0x00007f208578f3e2 in QEventLoop::exec (this=this@entry=0x7ffd1c34b880, flags=..., flags@entry=...) at kernel/qeventloop.cpp:204
#51 0x00007f208579702c in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1188
#52 0x00007f2085ad631c in QGuiApplication::exec () at kernel/qguiapplication.cpp:1510
#53 0x00007f20860977a5 in QApplication::exec () at kernel/qapplication.cpp:2956
#54 0x00007f208726d8c3 in kdemain (argc=3, argv=0x7ffd1c34bab8) at ../main_x11.cpp:294
#55 0x00007f2086ebfa40 in __libc_start_main (main=0x400790 <main(int, char**)>, argc=3, argv=0x7ffd1c34bab8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffd1c34baa8) at libc-start.c:289
#56 0x00000000004007c9 in _start ()

Reported using DrKonqi