Hello. I'm having issues with plasmashell freezing / becoming unresponsive after I unlock the screenlocker. It does not happen every time, but pretty frequently. Killing plasmashell and restarting it temporarily solves the problem. This is happening on the official arch linux packages, with mesa and a Radeon HD 5670/5690/5730. It could be a mesa bug as well. Reproducible: Sometimes Steps to Reproduce: 1. Leave computer, wait for lock screen to automatically appear 2. After a while, unlock the computer Actual Results: Plasmashell was frozen. Expected Results: A working plasmashell. The log output from plasmashell does not seem to display anything useful, this is the end of the log and I could see that plasmashell had been frozen for roughly 14 hours by looking at the clock widget: org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 261 "Properties" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 261 "Properties" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 262 "Volume" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 262 "Volume" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 268 "CardIndex" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 268 "CardIndex" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 269 "Ports" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 269 "Ports" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 270 "ActivePortIndex" org.kde.plasma.pulseaudio: returning roles QHash((264, "HasVolume")(267, "Description")(266, "Name")(269, "Ports")(268, "CardIndex")(270, "ActivePortIndex")(257, "Index")(259, "ObjectName")(258, "PulseObject")(261, "Properties")(260, "Index")(263, "Muted")(262, "Volume")(265, "VolumeWritable")) org.kde.plasma.pulseaudio: PROPERTY CHANGED ( 0 ) :: 270 "ActivePortIndex" libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok libkcups: Renew-Subscription last error: 0 successful-ok Note that the rest of the log is mostly PROPETY CHANGED lines, so it seems the dbus messages stops at one point, probably when it freezes. GDB traceback and thread info: Threads: Thread 9 has target name 'KCupsConnection' Thread 9 has target id 'Thread 0x7fff2fa25700 (LWP 23009)' Thread 8 has target name 'QQuickPixmapRea' Thread 8 has target id 'Thread 0x7fffc5f98700 (LWP 23005)' Thread 7 has target name 'plasmashell' Thread 7 has target id 'Thread 0x7fffccaf3700 (LWP 23004)' Thread 6 has target name 'QQmlThread' Thread 6 has target id 'Thread 0x7fffce469700 (LWP 23003)' Thread 5 has target name 'QQmlThread' Thread 5 has target id 'Thread 0x7fffd00ca700 (LWP 23002)' Thread 4 has target name 'plasmashell' Thread 4 has target id 'Thread 0x7fffd18e4700 (LWP 23001)' Thread 3 has target name 'QQmlThread' Thread 3 has target id 'Thread 0x7fffdbfff700 (LWP 23000)' Thread 2 has target name 'QXcbEventReader' Thread 2 has target id 'Thread 0x7fffe2d45700 (LWP 22999)' Thread 1 has target name 'plasmashell' Thread 1 has target id 'Thread 0x7fffe4830800 (LWP 22993)' [Thread 1 (Thread 0x7fffe4830800 (LWP 22993))] 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 (gdb) bt full #0 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 No symbol table info available. #1 0x00007ffff65b0ae2 in ?? () from /usr/lib/libxcb.so.1 No symbol table info available. #2 0x00007ffff65b2829 in xcb_wait_for_special_event () from /usr/lib/libxcb.so.1 No symbol table info available. #3 0x00007fffee850737 in dri3_find_back (draw=draw@entry=0x15021f8) at loader_dri3_helper.c:380 b = <optimized out> ev = <optimized out> ge = <optimized out> #4 0x00007fffee8514e0 in dri3_get_buffer (driDrawable=<optimized out>, draw=0x15021f8, buffer_type=loader_dri3_buffer_back, format=4099) at loader_dri3_helper.c:1193 buffer = <optimized out> buf_id = <optimized out> dri_context = 0xd11250 #5 loader_dri3_get_buffers (driDrawable=<optimized out>, format=4099, stamp=0x1533330, loaderPrivate=0x15021f8, buffer_mask=<optimized out>, buffers=0x7fffffffd2d0) at loader_dri3_helper.c:1370 draw = 0x15021f8 front = 0x0 back = 0x0 #6 0x00007fffd9799ca3 in dri_image_drawable_get_buffers (statts_count=<optimized out>, statts=<optimized out>, images=<optimized out>, drawable=<optimized out>) at dri2.c:279 pf = PIPE_FORMAT_Z24_UNORM_S8_UINT buffer_mask = 1 i = <optimized out> image_format = 4099 bind = 1 #7 dri2_allocate_textures (ctx=0xe2c560, drawable=0x1533330, statts=0x248d600, statts_count=2) at dri2.c:402 sPriv = 0x913ec0 dri_drawable = 0x23e9a50 templ = {reference = {count = 1}, screen = 0x6cf420, target = 1025, format = PIPE_FORMAT_NONE, width0 = 3898722504, height0 = 32767, depth0 = 0, array_size = 0, last_level = 48, nr_samples = 137, usage = 90, bind = 0, flags = 14799136} alloc_depthstencil = 0 '\000' i = <optimized out> j = <optimized out> bind = 0 image = 0x7fffeea719c0 <imageLoaderExtension> images = {image_mask = 0, back = 0x0, front = 0x0} buffers = 0x0 whandle = {type = 19, handle = 0, stride = 0} num_buffers = 2 #8 0x00007fffd979698c in dri_st_framebuffer_validate (stctx=<optimized out>, stfbi=<optimized out>, statts=0x248d600, count=2, out=0x7fffffffd460) at dri_drawable.c:83 ctx = 0xe2c560 drawable = 0x1533330 statt_mask = 18 new_mask = <optimized out> new_stamp = <optimized out> i = <optimized out> lastStamp = <optimized out> textures = 0x1533438 #9 0x00007fffd96bd38e in st_framebuffer_validate (stfb=0x248d1a0, st=st@entry=0xf07f80) at state_tracker/st_manager.c:201 textures = {0x8892, 0x20, 0x7fffffffd490, 0x7fffffffd4e0, 0x7fffffffd4e0, 0x0, 0x1} width = <optimized out> height = <optimized out> i = <optimized out> changed = 0 '\000' new_stamp = 3 #10 0x00007fffd96be8f9 in st_manager_validate_framebuffers (st=st@entry=0xf07f80) at state_tracker/st_manager.c:872 No locals. #11 0x00007fffd96681a6 in st_validate_state (st=st@entry=0xf07f80) at state_tracker/st_atom.c:194 state = 0xf09630 #12 0x00007fffd966f7d1 in st_Clear (ctx=0xed9310, mask=50) at state_tracker/st_cb_clear.c:473 depthRb = 0x2ab5000 stencilRb = 0x2ab5000 quad_buffers = 0 clear_buffers = 0 i = <optimized out> #13 0x00007ffff5e2444a in QSGBatchRenderer::Renderer::renderBatches() () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #14 0x00007ffff5e29e32 in QSGBatchRenderer::Renderer::render() () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #15 0x00007ffff5e35b2f in QSGRenderer::renderScene(QSGBindable const&) () from /usr/lib/libQt5Quick.so.5 No symbol table info available. ---Type <return> to continue, or q <return> to quit--- #16 0x00007ffff5e3637b in QSGRenderer::renderScene(unsigned int) () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #17 0x00007ffff5e4686e in QSGRenderContext::renderNextFrame(QSGRenderer*, unsigned int) () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #18 0x00007ffff5e9083b in QQuickWindowPrivate::renderSceneGraph(QSize const&) () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #19 0x00007ffff5e6120b in ?? () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #20 0x00007ffff5e62311 in ?? () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #21 0x00007ffff38159ac in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5 No symbol table info available. #22 0x00007ffff381ae86 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5 No symbol table info available. #23 0x00007ffff2d11bab in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #24 0x00007ffff2d6736d in QTimerInfoList::activateTimers() () from /usr/lib/libQt5Core.so.5 No symbol table info available. #25 0x00007ffff2d67871 in ?? () from /usr/lib/libQt5Core.so.5 No symbol table info available. #26 0x00007fffef3bedc7 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #27 0x00007fffef3bf020 in ?? () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #28 0x00007fffef3bf0cc in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #29 0x00007ffff2d6854f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #30 0x00007ffff2d0f57a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #31 0x00007ffff2d1753c in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5 No symbol table info available. #32 0x000000000043138a in main () No symbol table info available. [Switching to thread 2 (Thread 0x7fffe2d45700 (LWP 22999))] #0 0x00007ffff1c5307f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0 No symbol table info available. #1 0x00007ffff65b0d39 in ?? () from /usr/lib/libxcb.so.1 No symbol table info available. #2 0x00007ffff65b2757 in xcb_wait_for_event () from /usr/lib/libxcb.so.1 No symbol table info available. #3 0x00007fffe4460379 in ?? () from /usr/lib/libQt5XcbQpa.so.5 No symbol table info available. #4 0x00007ffff2b30b8e in ?? () from /usr/lib/libQt5Core.so.5 No symbol table info available. #5 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #6 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available. [Switching to thread 3 (Thread 0x7fffdbfff700 (LWP 23000))] #0 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 No symbol table info available. #1 0x00007fffef3befbc in ?? () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #2 0x00007fffef3bf0cc in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #3 0x00007ffff2d6854f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #4 0x00007ffff2d0f57a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #5 0x00007ffff2b2bbe4 in QThread::exec() () from /usr/lib/libQt5Core.so.5 No symbol table info available. #6 0x00007ffff5444055 in ?? () from /usr/lib/libQt5Qml.so.5 No symbol table info available. #7 0x00007ffff2b30b8e in ?? () from /usr/lib/libQt5Core.so.5 No symbol table info available. #8 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #9 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available. [Switching to thread 4 (Thread 0x7fffd18e4700 (LWP 23001))] #0 0x00007ffff1c5307f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0 No symbol table info available. #1 0x00007fffd9b1c923 in cnd_wait (mtx=0x94d450, cond=0x94d478) at ../../../../../include/c11/threads_posix.h:159 No locals. #2 pipe_semaphore_wait (sema=0x94d450) at ../../../../../src/gallium/auxiliary/os/os_thread.h:259 No locals. #3 radeon_drm_cs_emit_ioctl (param=param@entry=0x94d020) at radeon_drm_winsys.c:680 ws = 0x94d020 cs = <optimized out> i = <optimized out> #4 0x00007fffd9b1c047 in impl_thrd_routine (p=<optimized out>) at ../../../../../include/c11/threads_posix.h:87 pack = {func = 0x7fffd9b1c8d0 <radeon_drm_cs_emit_ioctl>, arg = 0x94d020} #5 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #6 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available. (gdb) thread 5 [Switching to thread 5 (Thread 0x7fffd00ca700 (LWP 23002))] #0 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 (gdb) bt full #0 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 No symbol table info available. #1 0x00007fffef3befbc in ?? () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #2 0x00007fffef3bf0cc in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #3 0x00007ffff2d6854f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #4 0x00007ffff2d0f57a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #5 0x00007ffff2b2bbe4 in QThread::exec() () from /usr/lib/libQt5Core.so.5 No symbol table info available. #6 0x00007ffff5444055 in ?? () from /usr/lib/libQt5Qml.so.5 No symbol table info available. #7 0x00007ffff2b30b8e in ?? () from /usr/lib/libQt5Core.so.5 No symbol table info available. #8 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #9 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available. [Switching to thread 6 (Thread 0x7fffce469700 (LWP 23003))] #0 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 No symbol table info available. #1 0x00007fffef3befbc in ?? () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #2 0x00007fffef3bf0cc in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #3 0x00007ffff2d6854f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #4 0x00007ffff2d0f57a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #5 0x00007ffff2b2bbe4 in QThread::exec() () from /usr/lib/libQt5Core.so.5 No symbol table info available. #6 0x00007ffff5444055 in ?? () from /usr/lib/libQt5Qml.so.5 No symbol table info available. #7 0x00007ffff2b30b8e in ?? () from /usr/lib/libQt5Core.so.5 No symbol table info available. #8 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #9 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available. [Switching to thread 7 (Thread 0x7fffccaf3700 (LWP 23004))] #0 0x00007ffff1c5307f in pthread_cond_wait@@GLIBC_2.3.2 () from /usr/lib/libpthread.so.0 No symbol table info available. #1 0x00007ffff786c934 in ?? () from /usr/lib/libQt5Script.so.5 No symbol table info available. #2 0x00007ffff786c979 in ?? () from /usr/lib/libQt5Script.so.5 No symbol table info available. #3 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #4 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available. [Switching to thread 8 (Thread 0x7fffc5f98700 (LWP 23005))] #0 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 No symbol table info available. #1 0x00007fffef3befbc in ?? () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #2 0x00007fffef3bf0cc in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #3 0x00007ffff2d6856b in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #4 0x00007ffff2d0f57a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #5 0x00007ffff2b2bbe4 in QThread::exec() () from /usr/lib/libQt5Core.so.5 No symbol table info available. #6 0x00007ffff5df4136 in ?? () from /usr/lib/libQt5Quick.so.5 No symbol table info available. #7 0x00007ffff2b30b8e in ?? () from /usr/lib/libQt5Core.so.5 No symbol table info available. #8 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #9 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available. [Switching to thread 9 (Thread 0x7fff2fa25700 (LWP 23009))] #0 0x00007ffff244518d in poll () from /usr/lib/libc.so.6 No symbol table info available. #1 0x00007fffef3befbc in ?? () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #2 0x00007fffef3bf0cc in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0 No symbol table info available. #3 0x00007ffff2d6854f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #4 0x00007ffff2d0f57a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5 No symbol table info available. #5 0x00007ffff2b2bbe4 in QThread::exec() () from /usr/lib/libQt5Core.so.5 No symbol table info available. #6 0x00007fff31cf4bc7 in KCupsConnection::run() () from /usr/lib/libkcupslib.so No symbol table info available. #7 0x00007ffff2b30b8e in ?? () from /usr/lib/libQt5Core.so.5 No symbol table info available. #8 0x00007ffff1c4d4a4 in start_thread () from /usr/lib/libpthread.so.0 No symbol table info available. #9 0x00007ffff244e13d in clone () from /usr/lib/libc.so.6 No symbol table info available.
I am experiencing similar problems on Fedora 23. I am currently running plasma 5.5.5 but the problem started with 5.5.4. At first everything seems to work fine. If the screen is switched off, moving the mouse or hitting the keyboard turns it back on and the shell is responsive. After some indeterminate amount of time, however, the shell will freeze after the screen is switched off. The system itself is not frozen; I can switch VTs, login and even start a new X session - it's just the original plasma session that is frozen. Killing the session and starting a new one does not help in that it will immediately freeze again as soon as the screen goes to sleep. The system must be restarted to "reset" things so that things work for at least a short period. As far as I can tell, the problem only occurs if "Screen Energy Saving" is enabled and the screen switches off. The "Dim Screen" setting makes no difference.
I would just like to notify that I have not been able to reproduce this issue after updating to plasma 5.6.0/5.6.1 and mesa-git from roughly two weeks ago. Not sure which of the packages that fixed the issue, but I have not encountered it for two weeks now and it used to happen several times a day. I will leave the issue open for others to comment on in case this issue is not resolved for everyone.
This crash is in your graphic driver and is really old. There is nothing we can do. Sorry.