Bug 89173

Other Kubuntu user seems to have the same problem:

https://bugs.launchpad.net/kubuntu-ppa/+bug/1422185

I forgot to mention my installation details:

Archlinux, with and intel graphics card

Please attach the full /var/log/Xorg.0.log file and the output of dmesg.

Created attachment 113547 [details]
Xorg.0.log

Created attachment 113548 [details]
dmesg

Please attach the stacktrace from kwin (using gdb and lots of debug packages for the symbols).

I have compiled and installed kwin with debug symbols, but i don't know how to debug it with gdb.

Once it freezes switch to vt and run "gdb --pid `pidof kwin`" and then type bt. It may not be called kwin but something similar so check first.

The process is called `kwin_x11` in Arch.

Error detected on fd 0
error detected on stdin
Starting program: /usr/bin/kate 
warning: Could not load shared library symbols for linux-vdso.so.1.
Do you need "set solib-search-path" or "set sysroot"?
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7fffe456b700 (LWP 1641)]
#0  0x00007fb5e6d9fead in nanosleep () from /usr/lib/libc.so.6
#1  0x00007fb5e54b01ad in ?? () from /usr/lib/libQt5Core.so.5
#2  0x00007fb5e53fa9d8 in QThread::msleep(unsigned long) () from /usr/lib/libQt5Core.so.5
#3  0x00007fb5e550c340 in QLockFile::tryLock(int) () from /usr/lib/libQt5Core.so.5
#4  0x00007fb5dedee989 in ?? () from /usr/lib/libKF5ConfigCore.so.5
#5  0x00007fb5dedd0c56 in KConfig::sync() () from /usr/lib/libKF5ConfigCore.so.5
#6  0x00007fb5e4021f13 in ?? () from /usr/lib/libKF5Plasma.so.5
#7  0x00007fb5e402a445 in ?? () from /usr/lib/libKF5Plasma.so.5
#8  0x00007fb5e5615339 in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib/libQt5Core.so.5
#9  0x00007fb5e56230a8 in QTimer::timerEvent(QTimerEvent*) () from /usr/lib/libQt5Core.so.5
#10 0x00007fb5e5616473 in QObject::event(QEvent*) () from /usr/lib/libQt5Core.so.5
#11 0x00007fb5e5ec3d8c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#12 0x00007fb5e5ec9370 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#13 0x00007fb5e55e5a9b in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#14 0x00007fb5e563bf6d in QTimerInfoList::activateTimers() () from /usr/lib/libQt5Core.so.5
#15 0x00007fb5e563a703 in QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#16 0x00007fb5d0c834ad in ?? () from /usr/lib/qt/plugins/platforms/libqxcb.so
#17 0x00007fb5e55e3532 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#18 0x00007fb5e55eaf0c in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#19 0x00007fb5e708f9fb in kdemain (argc=1, argv=0x7fffbca731f8) at /home/yo/builds/kwin/src/kwin-5.2.0.1/main_x11.cpp:294
#20 0x00007fb5e6d08800 in __libc_start_main () from /usr/lib/libc.so.6
#21 0x00000000004007d9 in _start ()
A debugging session is active.

	Inferior 1 [process 823] will be detached.

Quit anyway? (y or n) Detaching from program: /usr/bin/kwin_x11, process 823

Created attachment 113600 [details]
kwin trace

I am not sure if the last trace was of kwin. I have repeat the procedure again and this is the result. Is attached as trace2.log file.

Created attachment 113601 [details]
trace2.log

(In reply to kiko loche from comment #12)
> I am not sure if the last trace was of kwin. I have repeat the procedure
> again and this is the result. Is attached as trace2.log file.

The first trace was of kate, the second from kwin. Can you repeat that a couple of times to see if kwin is advancing or always waiting for that reply?

Created attachment 113612 [details]
trace3.log

Created attachment 113613 [details]
trace4.log

Some aclarations:

In trace3.log I didn't wait plasma 5 freeze. I switched to vt before and run gdb.

In trace4.log I waited until plasma 5 freeze. Then I switched to vt and run gdb.

trace3 is nice and boring. trace4 is in a different location to trace2. Still it suggests that it is not kwin that is freezing, so I have no idea why it appears to become unresponsive.

Created attachment 113647 [details]
trace5.log

Created attachment 113648 [details]
trace6.log

I have repeated the procedure twice (trace5.log and trace6.log). Perhaps ...

3 traces now repeating that QLockFile::tryLock() -> nanosleep() pause. I suggest raising it with kwin/kde devs first to see if they have suggests to debug that particular lockup. Alternatively, you can try downgrading components to see if the freeze goes away - it may be related or a even a different bug altogether.

Ok. I have sended them  the information about this thread.

The problem was a corruption state of svg cache. I resolved the problem with the following commands:

rm -fr ~/.cache/plasma*
rm -fr ~/.cache/ksycoca*
rm -fr ~/.cache/*.kcache
kbuildsycoca5